what is your hypothesis for the ice experiment

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The Chaos and the Clutter

Melting Ice Experiment

By Sharla Kostelyk

(This post may contain affiliate links. For more information, see my disclosure policy .)

This is a simple science experiment to do with items you likely already have in your kitchen. Our daughter wanted to do her Science Fair project on melting ice. She was curious about what would make ice melt faster. 

Melting Ice Science Experiment:

Supplies needed:

• small Dixie cups or mini Solo cups
• 6 compartment muffin tin

Directions:

• Before beginning the experiment, have students talk about what they expect the results to be. Ask them what variable will melt the ice fastest. If you want, you can have them write down their hypothesis. 
• Fill 6 small Dixie cups or mini Solo cups with water. Place the cups on a baking tray and place the tray in the freezer.
• Freeze overnight.
• Cut the frozen water out of the paper cups (adult help may be required for this step). If using Solo cups , you won’t need scissors as you should be able to just pop the ice out.
• Place one ice cup in each of the compartments in the muffin tin. Pour hot water on one, cold water on another, steam on another, salt on another, and sugar on another.* Leave one alone so that it can act as the control.

*Adult supervision is important, particularly with the steam and hot water.

Students can document the progress through taking pictures or journalling observations at one minute, five minutes, half an hour, and one hour after adding the variables.

Here is a picture before we added anything to the ice:

Our daughter dictated to me what she had observed during the experiment and we included that as well as a picture she drew of the process and the photographs on her display board  for the Science Fair . She loved presenting and explaining her findings to the judges.

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Classroom Activity

Melting ice experiment.

In this activity, students will predict, observe, and compare melt rates of ice under different temperature conditions and in different solutions.

Cool and warm water

Ice cubes (4-6 per group, uniform size and shape)

Food coloring

Thermometers

Colander, mesh strainer, or other similar device

Small bowls (2 per group)

Cloth or paper towels

(Optional) pitchers for pouring water

(Optional) basin for catching poured water

(Optional) funnels

• This activity requires flowing water. If available, a faucet with cold and warm water can be used. Otherwise, use pitchers with warm and cold water. However, note that the rate at which water is poured from a pitcher can vary greatly. Pouring through a funnel can help regulate the flow of water.
• Consider having towels on hand for cleaning up spills and splashes.
• Safety: Hot water can scald. Make sure students are using water that is below 110° F (43° C).
• Use the leftover water from this activity to water a plant or save it for another activity instead of dumping it down the drain.

The Greenland ice sheet is the second largest body of ice in the world right behind the Antarctic ice sheet. As the ice sheet melts, the water flows into the ocean, contributing to global sea level rise.

As glacier ice melts, some of the water can reach the ground below the ice, forming a river that channels glacier water into the ocean. As it flows into the ocean, this cold, fresh meltwater will rise above the warmer, salty ocean water because freshwater is less dense than salt water.

The rising cold water then draws in the warmer ocean water, melting the face of the glacier from the bottom up. This creates an overhang of ice, the edges of which will eventually break off in a process called calving, which quickly adds more ice to the ocean. As ocean waters warm, this calving process speeds up.

This narrated animation shows warm ocean water is melting glaciers from below, causing their edges to break off in a process called calving. Credit: NASA | Watch on YouTube

Understanding these different factors that contribute to Greenland's melting ice sheet is an important part of improving estimates of sea level rise. The Oceans Melting Greenland (OMG) mission was designed to help scientists do just that using a combination of water temperature probes, precise glacier elevation measurements, airborne marine gravity, and ship-based observations of the sea floor geometry. The mission, which ran from 2016 to 2022, provided a data set that scientists can now use to model ocean/ice interactions and improve estimates of global sea level rise.

Part 1: Still Water

Part 2: flowing water, part 3: salt and freshwater.

• Introduce or ask students what they know about glaciers, ice melt, and sea level rise. Consider using the lesson What’s Causing Sea-Level Rise? and having students read 10 Interesting Things About Glaciers from NASA's Climate Kids website prior to this activity. If necessary, remind students that glaciers are huge, long-lasting masses of ice sitting on landmasses that form over many years. Snow accumulates and compresses into glacier ice under the weight of newer layers of snowfall above. Glaciers are not to be confused with icebergs, which are large chunks of glaciers or ice sheets that have broken off and float freely in the ocean.

Fill one container with room-temperature water and a second container with hot water. Image credit: NASA/JPL-Caltech | + Expand image

Place an ice cube in each container of water and time how long it takes the ice to melt. Image credit: NASA/JPL-Caltech | + Expand image

• Ice cube placed in a dish of room temperature water
• Ice cube placed in a dish of hot water
• Ice cube placed under flowing room temperature water
• Ice cube placed under flowing hot water
• Fill one dish with room temperature water.
• Measure and record the temperature.
• Gently place an ice cube in the dish and record how long it takes for the ice cube to melt. There should be enough water in the dish so the ice cube floats.
• Measure and record the water temperature after the ice has melted.
• Repeat the procedure using hot water. These two steps can be done at the same time if students are able to monitor and record the melt time for both cubes of ice.
• Ask students to share their results and observations.

Image credit: NASA/JPL-Caltech | + Expand image

• Mix water with food coloring and freeze into ice cubes (two per group or two as a class demo).
• Tell students they are going to add a colored ice cube to a saltwater solution and to a freshwater solution and allow the ice to fully melt. Ask them to make predictions about what will happen.
• In a clear beaker or plastic container, add 1 teaspoon of salt to 1 cup of water and stir until the salt is dissolved. Allow time for any water movement to stop.
• Pour the same amount of freshwater into a clear beaker or plastic container. Allow time for any water movement to stop.
• Gently add one ice cube to each container, taking care to not disturb the water too much.
• Have students observe each container and take notes. It may be helpful for students to place a white sheet of paper behind the containers to see more details.

The cup on the left (with blue food coloring) contained ice melted in a saltwater solution while the one on the right (with the red food coloring) contained ice melted in a freshwater solution. Image credit: NASA/JPL-Caltech | + Expand image

• If necessary, explain to students that because one container has salt water, and one has freshwater, the less dense meltwater floats on salt water but has the same density and mixes with the freshwater.
• Connect this phenomenon to the movement of fresh meltwater from under a glacier into warm ocean water.
• Which ice cube melted fastest? Which melted slowest? How could these results be altered? Changing the flow rate and temperature of the water will change how quickly the ice melts.
• What do these results tell you about the melting of glaciers in different conditions? Currents of warm ocean water will melt glaciers faster than still water.
• What would happen to cold meltwater that flows out from under a glacier into salty ocean water? The freshwater will rise because of its lower density, drawing in warmer ocean water against the face of the glacier.
• Students should accurately measure and record temperature and melt times.
• High school chemistry students should accurately calculate what the final temperature of the water in the containers will be in Part 1 by using specific heat capacity.
• Ask students to investigate whether ice exposed to warm or room temperature air would melt more quickly or more slowly than ice exposed to still or flowing warm or room temperature water.
• Lower elementary: Ask students to predict what would happen if some of the water was removed from the containers in Part 1 and placed in the freezer. Freeze some of the water to confirm their predictions.
• Upper elementary: Remove some of the salt water from Part 3 and place it on a flat, non-porous surface to dry. Ask students to predict what will happen when the water evaporates. Repeat the process with freshwater. Allow water to dry overnight and compare predictions to observations of what occurred.
• Middle school: Ask students to draw or describe the changes in particle motion, temperature, and state(s) of matter at the beginning and end of their observations.
• High school: Using the known masses and temperatures of the ice cubes and water in Part 1, have students calculate the final temperature of the water in the room temperature bowl and the hot water bowl using the formula m 1 CΔT 1  = m 2 CΔT 2 . Then, have them compare their calculations to observed results.

Explore More

What's Causing Sea-Level Rise? Land Ice Vs. Sea Ice

Students learn the difference between land ice and sea ice and make a model to see how the melting of each impacts global sea level.

Subject Science

Time 30 mins - 1 hr

10 Interesting Things About Glaciers

Learn all about glaciers in this slideshow from NASA's Climate Kids website

Time Less than 30 mins

Lessons in Sea-Level Rise

What is sea-level rise and how does it affect us? This "Teachable Moment" looks at the science behind sea-level rise and offers lessons and tools for teaching students about this important climate topic.

Grades 5-12

Time 30-60 mins

Collection: Climate Change Lessons for Educators

Explore a collection of standards-aligned STEM lessons for students that get them investigating climate change along with NASA.

How Melting Ice Causes Sea Level Rise

Learn the difference between land ice and sea ice, then do an experiment to see how the melting of each contributes to global sea level rise.

Collection: Climate Change Activities for Students

Learn about climate change and its impacts with these projects, videos, and slideshows for students.

Teachable Moments: Reflecting On Greenland’s Melting Glaciers as OMG Mission Concludes

Explore how the OMG mission discovered what's behind one of the largest contributors to global sea level rise. Plus, learn what it means for communities around the world and how to get students engaged.

NASA Greenland Mission Completes Six Years of Mapping Unknown Terrain

To learn how ocean water is melting glaciers, NASA’s Oceans Melting Greenland mission extensively surveyed the coastline of the world’s largest island.

Easy and Painless Instant Ice Science Fair Project

Categories Science Experiments

Instant ice experiments are a lot of fun! Here’s how to turn your ice science activities into an instant ice science fair project!

If you are on the hunt for science fair projects, you’re probably a parent. 😀

And most of us don’t have a lot of time to help coach our kids through detailed, never-ending science fair projects.

So of course we want easy science fair projects to suggest to them to keep the family’s mental health on track.

The instant ice science fair project fits this need *perfectly.* Painless science fairs all around!

How to Do an Instant Ice Science Fair Project

When you do a science fair project, the first thing do to is create a hypothesis! Here are some good hypothesis questions to ask when making instant ice.

Instant Ice Experiment Hypothesis

Here are some questions you can ask for an instant ice science fair project.

• What was the optimum temperature of the water?
• How long did the reaction last?
• How long did it take the water to reach the instant ice stage?
• Will the experiment work with tap water or rainwater?

Instant Ice Experiment Explanation

Instant ice is a curious thing! It works by the domino effect of science, nucleation!

Nucleation is the process by which a reaction spreads to nearby molecules, just like dominos falling in a row.

Distilled water has no impurities for ice crystals to form around. This means that at *just* the right temperature, the water will be liquid but have the potential to form ice because it’s below freezing.

This is the sweet spot for instant ice!

Instant ice won’t work if you use water that has impurities like tap water or rainwater.

How Long Does It Take to Make Instant Ice?

It varies depending on your freezer’s temperature, but in most cases, it will take anywhere from 30 minutes to two hours to get the water cool enough to make instant ice.

What Do You Need to Do the Instant Ice Science Fair Project?

Shop the Amazon affiliate links below for everything you need to do this science fair project!

Instant Ice Video!

Watch the video of making ice crystals below!

Instant Ice Experiment Procedure

Here’s how to do the instant ice science experiment.

First, decide on the hypothesis that you want to use. Write that in your science notebook or our instant ice worksheets.

Step two is to test variables. You can test them all at once or one at a time. You’ll probably want to have at least a case of distilled water to make sure you have enough water for all of your tests.

Make the instant ice by supercooling your bottles in the freezer. You’ll know if it’s ready if you can pour out the water on an ice cube and a little tower forms.

Hit or tap the bottles to create crystals inside the bottle, or pour it out to make an instant ice tower.

More Ice Science Experiments

Can You Burn Ice? Burning Ice Experiment (not for young kids!)

How to Make an Ice Magnifying Glass (start a fire with ice?!)

How to Make Instant Ice in 5 Seconds

Colorful Melting Ice Experiment

Share this project with a friend!

Scientific Method: Step 3: HYPOTHESIS

• Step 1: QUESTION
• Step 2: RESEARCH
• Step 3: HYPOTHESIS
• Step 4: EXPERIMENT
• Step 5: DATA
• Step 6: CONCLUSION

Step 3: State your hypothesis

Now it's time to state your hypothesis . The hypothesis is an educated guess as to what will happen during your experiment. 

The hypothesis is often written using the words "IF" and "THEN." For example, " If I do not study, then I will fail the test." The "if' and "then" statements reflect your independent and dependent variables . 

The hypothesis should relate back to your original question and must be testable .

A word about variables...

Your experiment will include variables to measure and to explain any cause and effect. Below you will find some useful links describing the different types of variables.

• "What are independent and dependent variables" NCES
• [VIDEO] Biology: Independent vs. Dependent Variables (Nucleus Medical Media) Video explaining independent and dependent variables, with examples.

Resource Links

• What is and How to Write a Good Hypothesis in Research? (Elsevier)
• Hypothesis brochure from Penn State/Berks

• << Previous: Step 2: RESEARCH
• Next: Step 4: EXPERIMENT >>
• Last Updated: Aug 26, 2024 10:04 AM
• URL: https://harford.libguides.com/scientific_method

Instant Ice: Winter Science Experiment for Kids

My kids love science projects that involve something that looks just a bit like magic. We’ve had a lot of fun making glow-in-the-dark projects, flying projects, and anything that has a “wow” factor. This winter, we resolved to try and make instant ice. We knew the project could be a bit tricky, but we didn’t have any problems with it at all! The experiment turned out just as it ought to, which is always a great feeling!

Watch ice form before your very eyes in this fun science experiment!

You’ll need just a few things for this project:

• Water bottles (we used a dozen, just in case!)

Place 6-12 water bottles in your freezer (or you can do it outside, but the temperature is less predictable out there). Lay them flat on their sides rather than upright. For some reason, they freeze better this way. If your kids want to experiment, place some upright and some on their sides and see which one works best!

Cool the water for about two to two and a half hours. At the two hour mark, take out one bottle and test it. If you can slam it on the counter and nothing forms, the water isn’t cool enough yet. When you get one that hardens, it is ready to go, but you’ll have to work quickly!

Turn bowl upside down over a towel (to catch the spills) and place a large ice cube on the bowl.

Carefully pour the water slowly onto the ice cube.

The water will create a column of frozen ice!

In about 20 seconds, the water will get too warm for this trick to work. But you can repeat it with all the water bottles you have!

Instant Ice Science Explained

The trick to this experiment is super-cooled water. You’re catching the water when it is cold enough to freeze, but hasn’t quite frozen yet. When ice freezes, the water forms small crystals that gradually spread. If you catch the cold water before the crystals have time to form, you can still pour out the water and it will freeze as you pour. Pouring it over an ice cube triggers crystals to form faster than they normally would.

You can get a similar effect by smashing a still-closed bottle of super-cooled water onto a hard surface. This triggers the crystals to form, instantly hardening the ice inside the bottle. The weather term for this process is called a “snap freeze.”

Ice Science Vocabulary

Celsius – Celsius (or “degrees Celsius”, or sometimes “Centigrade”) is a temperature scale. It is used to tell how hot or cold something is and is often written as °C. Water will freeze at 0°C and boil at 100°C

Fahrenheit – is also a temperature scale, typically used in the United States. We use it to tell how hot or cold something is. It is often written as °F. Water will freeze at 32°F and boil. at 212°F.

Snap-freeze –  a term used to describe a process by which a scientific sample is lowered to temperatures below -70 °C, very quickly. This is often accomplished by submerging a sample in liquid nitrogen. This prevents water from crystalizing when it forms ice, and so better preserves the structure of the sample.

Liquid Nitrogen – Nitrogen turns liquid at -210 degrees Celsius or  -346 degrees Fahrenheit. When nitrogen is liquid, it looks a lot like water.

Looking for more activities for kids?

We have a new option that offers new, creative activities all month long for you and your child!

The Learner’s Lab is the  community created  just for your family.  It’s full of creative lessons, problem solving activities, critical and divergent thinking games, and the social-emotional support  children and teens need most.

All from the comfort of your own home. 

We invite you to join us. Get all the details HERE.

More fun science for kids:

It’s a wonderful world — and universe — out there.

Come explore with us!  

Science News Explores

Build ice towers with bottled water and ice.

Add cold water and salt to create the conditions for your own mini ice castle

Bottles of water can be poured to create a tower of solid ice if the water is cold enough.

Doram/iStock/Getty Images Plus

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• Google Classroom

By Bethany Brookshire

September 16, 2020 at 6:30 am

This article is one of a series of  Experiments  meant to teach students about how science is done, from generating a hypothesis and designing an experiment to analyzing the results with statistics. You can repeat the steps here and compare your results — or use this as inspiration to design your own experiment.

In the Disney movies Frozen and Frozen II , Elsa uses magical powers to make castles of ice. We can’t build castles, but we can pour out small ice towers. Elsa may have magic. We use science. 

In an earlier experiment, I showed that sugar seed crystals are important for making rock candy. Those crystals provide a nucleation point where the sugar structure — the candy — can self-assemble. But sugar isn’t the only substance that can form a structure with the right nucleation point. Water can, too. It just needs to be super cool.

If you pour extremely cold water (water that’s less than 0° Celsius or 32° Fahrenheit) onto an ice cube, that cube acts as a nucleation point. The water will freeze when it hits the cube, and then stack up — forming a tower of ice.

If the water isn’t cold enough, though, you just get a lonely ice cube in a puddle of water.

As water freezes at 0 °C, I need a way to chill water to cooler than that. And I can’t let it freeze until it comes into contact with the cube. How? The secret is salt.

Saltwater has a lower freezing point than freshwater. This is why you can spread salt on an icy sidewalk and the ice will melt. Salt crystals in the water prevent the water molecules from linking up to form a crystal. Saltwater needs to be even colder than freshwater to freeze — cold enough that the salt gets pushed out of the water’s crystal structure. Freshwater freezes at 0 °C (32 °F), but saltwater freezes at –2 °C (28.4 °F).  

Is salt the difference between an ice tower and a puddle? I’m going to do an experiment to find out.

I need to start with a hypothesis — a statement I can test. Here, my hypothesis is: Water chilled in ice with salt will be colder and form taller ice towers than water chilled in water without salt .

To test this, I start with two small coolers. One cooler just has ice. The second cooler has ice mixed into a slush with salt.

I place bottles of purified water into each cooler. Be careful to check the label when you buy the water. The water should be purified or distilled. It should contain no added minerals. Those minerals might serve as nucleation points — making the bottled water freeze into a solid block of ice as soon as it gets cold enough to freeze. But if the water is pure, it should be able to get colder than 0 °C (32 °F) and stay a liquid.

Just one bottle of water in each cooler isn’t enough. I want to make sure that I can collect enough data to detect a difference between water chilled in fresh or salty ice. So I put eight bottles of water into each cooler.

Here’s how how to build ice towers:

• Fill two smaller coolers with ice (or you can use one cooler, and run the experiment twice).
• In one cooler, add 700 grams of salt (24.7 ounces, or about 2.5 cups). With a spoon, mix the salt and ice together very well. The ice will immediately start melting into a thick slush.
• Sink eight bottles of purified water into each cooler (for a total of 16). Make sure the bottles are each evenly surrounded with ice or slush.
• Wait 25 minutes.
• Gently rotate the bottles in the ice or slush. Make sure you do not shake the bottles.
• Wait another 20 minutes.
• Take the temperature of the bottles. I did this with a no-contact thermometer, but you can also use a regular thermometer; sink it into the ice next to the bottles.
• Place an ice cube on a plate. Using a ruler, measure the height of the cube.
• Remove a bottle of water carefully from the ice or slush and open it. Again, be careful not to shake it. (If you shake the super-cooled water, air inside the bottle will mix with the water. That creates nucleation points — and your bottled water will freeze before you open it.)
• Gently and slowly pour a small, steady stream of water onto the ice cube. After a second or two, the water will begin to freeze on top of the cube, producing an ice tower.
• Quickly whip out your ruler and get the height of your ice tower before it melts. (A friend is helpful for this.)
• Repeat until you’ve tested all 16 of your bottles.

Results on ice

To calculate how much ice I was able to grow, I subtracted the height of the ice cube from the height of the final ice tower. I added that to a spreadsheet with the temperature of each ice bottle.

The bottles chilled in ice got pretty cold — an average of 1.16 °C (34.1 °F). But the bottles chilled in salt slush got colder — an average of –2.65 °C (27.2 °F).

To confirm that these two groups are indeed different, I need to run statistics . These are tests to interpret the meaning of my results. I ran a t test. This test finds differences between two groups. Lots of websites online will let you plug your data in to run these tests for free. I used one from GraphPad Prism .

The test gave me a p value. It’s a measure of how likely it is that I would by accident find a difference as big as the one I found here. Many scientists consider a p value of less than five percent (0.05) to be statistically significant. This means that I would have a five percent chance of finding a difference that size by accident alone. If the p value I get is less than 0.05, I have a statistically significant difference.

For the two temperatures in my experiment, the p value was 0.0001, or 0.01 percent — definitely significant.

But just because there is a difference doesn’t mean that this difference is large. Tiny differences can be statistically significant. So I also ran a Cohen’s d test. Here I had to calculate my standard deviation. This is the amount that each set of data differs from the mean (or average). You can calculate that in any spreadsheet on a computer. On mine, I used Microsoft Excel, and used the function “= STDEV” and highlighted my data set. Then I put my mean, standard deviation and number of samples into this online calculator .

My Cohen’s d result was 2.93. Many scientists consider a Cohen’s d higher than 0.8 as a large effect size. So, the water cooled in the salt slush was definitely colder than the water cooled in simple ice.

As for the towers I built, the difference looked pretty obvious. When I poured out the bottles chilled in clean ice, I just got a puddle of water around my ice cube. Not a single one grew a tower. The difference between the ice cube and the final tower height was zero every time. But my saltwater-chilled bottles produced visible towers. Their average height was 5.66 centimeters (2.22 inches).

I ran statistics for these results as well. The p value for my final towers was 0.0001. My Cohen’s d was 4.13. Salt water made a very big difference in tower height.

My hypothesis when I started was that water chilled in ice with salt will be colder and form taller ice towers than water chilled in water without salt . Based on my results, it seems I was right. Salt helped water get colder and grow taller towers.

In every experiment, there are always things I could have done differently. In this one, I ended up with only six usable saltwater-chilled water bottles. The other two froze. Water in those bottles may not have been quite as “pure” as advertised on the label. I would probably chill extra bottles next time. Not only that, I didn’t always pour out the exact same quantity of water. Next time, I could weigh my results, and make sure that I poured out the same mass of water each time. That might help me get even more accurate results.

Luckily, this experiment is cheap. And I can easily run it again.

• Ice (two bags): $1.99 each
• Purified water (two packs of eight): $3.28 each
• 9-quart cooler (two): $9.97 each
• Salt (three pound box): $2.63
• Handheld infrared thermometer: $18.00
• Ruler: $0.97

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How Does Salt Affect Ice? A Simple Science Experiment

Looking for a way to explain to your learners why salt is utilized to combat icy roadways and sidewalks? Check out this simple science experiment to demonstrate how salt affects the freezing point of water and how the over-utilization of salt can be harmful to the environment.

Every winter before a storm, large trucks rumble down the road through my neighborhood, spreading salt crystals over the pavement. My six-year-old was curious about why these trucks appeared before a storm and so I decided to not only tell him but to show him, with a simple science experiment.

The Simple Science of Water and Salt

To provide my kids with a bit of background information, I broke out my chemistry modeling set and gave them a brief description of what’s happening at the molecular level.

Water is a molecule that is made up of two elements: hydrogen and oxygen. Water, also written as H 2 O, freezes at 0℃ or 32℉. However, when a compound like sodium chloride, NaCl, what we commonly refer to as salt, is dissolved in water, something interesting happens. The salt compound breaks apart into sodium and chlorine ions and prevents the water molecules from bonding together at their normal freezing point of 0℃ or 32℉. The addition of salt actually lowers the freezing point of water! 

When this occurs, we can’t actually see the sodium and chlorine ions at work, as they are way too small for our eyes to observe. What we do notice is that, when salt is applied to ice, the ice begins to melt. This is because the composition of water is no longer plain H 2 O; it now has sodium and chlorine ions floating around in it, causing the freezing point to decrease.

How’s that for some snazzy science?

Making the Science of Salt and Water Visible

In order to visualize the concept of salt lowering the freezing point of water, I gathered a few simple supplies from my kitchen and got to work. This experiment took approximately 30 minutes for my kids to complete from start to finish, with additional time to discuss the environmental implications of adding salt to icy roadways.

Materials Needed for the Science Experiment

To demonstrate how salt affects the freezing point of water, you’ll need the following materials:

• 2 Ice cubes
• Table salt*
• Timer or Clock

*You can use either fine or coarse table salt for this experiment. I chose to use both to demonstrate the difference in melting time for each option. If you want to test both salt types as well, you will need 3 ice cubes and 3 bowls.

Make Predictions to Practice Critical Thinking Skills

To engage your learners in critical thinking (and to add an extra layer of fun to the science experiment!) have them make the following predictions prior to conducting the experiment:

• Which ice cube will melt the fastest?
• How much time will it take for the plain ice cube to melt?
• How much time will it take for the salty ice cube to melt?

Not only do these questions get students thinking about the experiment, but they also allow them to make mathematical comparisons to the results, engaging the “M” in STEM! Have your learners record their predictions in a table, like the one shown below. 

Title: What Effect Does Salt Have on Ice?

I’ll explain more about teaching students how to collect data in an organized manner in the data collection portion of this post.

Most importantly, this is a fun activity to get your kids thinking and making hypotheses. Most children are afraid of being “wrong”; this activity teaches them that being wrong is part of the fun! Taking educated guesses is what drives science forward because when we realize our answer is wrong, we can confidently move forward in the right direction! Try to foster the idea that it’s not the “right” or “wrong” answer that’s important, but rather the learning that happens as a result of the experiment.

Instructions to Conduct the Salty Ice Experiment

Follow these step-by-step instructions to visualize the effect salt has on the ice.

• Set the bowls on a level surface.
• Place an ice cube in each bowl.
• Label the first bowl as your control. This bowl will only contain an ice cube.
• Label the second bowl as your variable. 
• Into the second bowl, pour one teaspoon of table salt on top of the ice cube.
• Record the time or start a stopwatch
• Observe the difference in the time it takes for the two ice cubes to melt.

If you have chosen to test the effect that both fine and coarse table salt have on the ice cubes, add a step to the instructions, applying one teaspoon of the additional salt to a third ice cube.

The temperature of the surrounding air will affect the rate at which both ice cubes melt. You want to specifically focus on the difference in time between the melting rates of the ice cubes.

Simple Data Collection for the Science Experiment

This is a great activity to introduce or reinforce the importance of recording data in an organized manner. Create a simple table like the one below for your learners to write down their observations. Point out that a table must have a title, clear labels explaining what each value represents, along with the units of measurement used.

Here is an example of a table to use for the salty ice experiment:

If you have chosen to test an additional type of table salt, be sure to add an extra column to the table.

Discussion Questions for the Salty Ice Experiment

Once your learners have completed the salty ice science experiment, have them revisit their predictions and compare them to the results. Try to avoid statements such as, “Were your predictions right or wrong?” as the aim is not for them to be accurate in their assumptions, but instead to learn how to properly conduct an experiment and analyze results. Here are some prompts you can try to get them thinking:

• Which ice cube changed from solid to liquid first? Why do you think that happened?
• How does the melting time of the plain ice cube compare to your prediction? Did it melt faster or slower than you predicted?
• How does the melting time of the salted ice cube compare to your prediction? Did it melt faster or slower than you predicted?
• How can this knowledge be useful to someone that lives in a climate zone that receives ice and snow in the winter?

Depending on the age and ability level of your learners, have them calculate the numerical difference in predicted versus actual melting times of each ice cube to add an extra mathematical component to this lesson.

Environmental Implications of Using Salt to Decrease Ice Accumulation on Outdoor Surfaces

To apply what they have learned, introduce and discuss the environmental issues that arise when salt is applied in abundance to icy roadways and outdoor surfaces. You can utilize the video lesson I created with Medinah Eatman of Science Teacher Mom to guide this portion of their learning, beginning at the Nature Connection section, found at minute 15 of the virtual lesson. You’ll notice that I reference a printable in the video, which you can access for free here:

Here are the main takeaways from this section of the lesson:

• Excess salt washes into local waterways, causing problems for the plants and animals that reside there.
• Fresh water fish that reside in local waterways have hatchlings that are 30% smaller than average when exposed to higher salinity. Salinity is a value that addresses the amount of salt dissolved in water. 
• Increased salinity in freshwater can kill zooplankton and phytoplankton, which are important food resources for fish, clams, snails, and insects.
• Plants can be negatively affected by increased salinity, causing them to have smaller leaves, flowers, and fruit, as well as slower stem growth.
• Large mammals like deer and moose are attracted to the salted roadways, causing in increase in collision rate with these animals during winter months.

The lesson then goes on to discuss the appropriate level of salt to use per area of ice, as well as some salt alternatives currently available to treat icy surface conditions.

Making Science Easily Accessible

Conducting simple scientific experiments like this one allows students to see that science is everywhere and doesn’t require fancy equipment to conduct investigations. Additionally, their confidence in making predictions and interpreting information will grow, strengthening their critical thinking skills.

If you try this salted ice experiment, please let me know by tagging me @thoughtfullysustainable on Instagram or Facebook , or by leaving a comment below! If you have any questions, feel free to email me!  

Instructions

1. Set the bowls on a level surface. 2. Place an ice cube in each bowl. 3. Label the first bowl as your control. This bowl will only contain an ice cube. 4. Label the second bowl as your variable. 5. Into the second bowl, pour one teaspoon of table salt on top of the ice cube. 6. Record the time or start a stopwatch 7. Observe the difference in the time it takes for the two ice cubes to melt.

You can use either fine or coarse table salt for this experiment. I chose to use both to demonstrate the difference in melting time for each option. If you want to test both salt types as well, you will need 3 ice cubes and 3 bowls.

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Dry Ice Experiments Your Students Will LOVE!

Have your students ever explored the phenomenon of sublimation !

If you’re ready to take your classroom to a new level of excitement, keep reading!

Every year I look forward to the Sublimation Stations lab with dry ice !

There are so many ways to integrate it into the curriculum! It’s a fun way to extend a matter unit . This station inquiry is also a great way for students to practice writing a hypothesis and making observations !

The end of October is always fun for this lab! It is a great way to “celebrate” Halloween in middle school without candy, costumes or a party. This lab IS THE PARTY!

Dry Ice Demonstration

Sublimation is the process of changing from the state of a solid to a gas. An awesome way to introduce sublimation is with the candle demo .

Pour several pieces of dry ice into a beaker. Show the students a lit candle. Ask the students to make a hypothesis about what will happen when you “pour” the dry ice onto the candle.

As your students watch the demo, they will observe that the flame will go out. They will also observe that the vapor coming off of the cup goes down, unlike hot steam, which rises.  This is due to the temperature difference and the density of the CO 2 gas which is heavier than air.  Also, it does not provide oxygen for combustion.

After discussing this dry ice experiment with your class, I like to let them loose with the sublimation stations.

Dry Ice Inquiry Based Stations for Kids

I have created a set of six inquiry based dry ice stations for students to explore . Each station uses commonly found household objects (such as a popsicle stick, balloon, and penny) to investigate dry ice.

These dry ice experiments are a great way for your students to practice following simple instructions, making a hypothesis, and writing observations.

I also encourage my students to write an explanation for “why” they the dry ice is behaving that way to encourage them to think about the “science” behind the fun!

Early finishers love to design their own dry ice experiment – teacher approved of course!

Dry Ice Safety Precautions

• Use tongs to handle dry ice.
• Do NOT hold the dry ice in your hand for a long period of time.  It will not hurt you to touch it for a second of two, but if you try to hold it, it can freeze your skin and feel like a burn. 
• Never put dry ice into a closed glass container. 
• Do NOT put dry ice into your mouth. 
• Use appropriate eyewear.

Tips for purchasing and storing dry ice:

• It’s all in the planning! Since dry ice “melts” over time, it’s best to get it as close as you can to when you will be using it. Store the dry ice in an insulated cooler. Be sure to keep the lid on top until you need to remove pieces for the activity. If there is space in the cooler, you may want to pack it with newspapers to insulate it and help it last longer.
• Slab vs Pellets – Pellets can be easier to handle for activities, but tend to “disappear” faster if you don’t use it quickly enough.
• Often you can find dry ice at your local Kroger. Walmart and Costco often have dry ice as well – it’s best to call ahead of time and pick it up the morning you are using it.
• Often fundraisers (such as cookie dough) are shipped in dry ice. Our science department fights over every shipment – it’s free fun!

Sublimation Stations Inquiry Lab

In this product you will find:

• Dry Ice Background Information
• Materials list (household items)
• Dry Ice Demo Directions
• Explanation of each phenomena for teachers
• 6 directed stations
• 1 design your own experiment station
• Student handout
• Black and white version for ease of printing

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Science project, water salinity.

Do you think water from your faucet freezes the same as water from the ocean? While you probably know that all water is made up of hydrogen and oxygen molecules, water from the ocean also has an extra ingredient: salt! In this project, you'll discover whether or not the presence of salt -- sometimes referred to as salinity -- affects water's ability to freeze.

Will increasing the amount of salt in water effect how slow or fast the water freezes?

• Package of clear plastic disposable cups
• Measuring cup
• Iodized salt
• Measuring spoons
• Stirring spoons
• Small clock with minute and second hand or a stopwatch
• Set three cups on the table.
• Measure ½ cup water into each plastic cup.
• To the first cup, add no salt.
• To the second cup, add 1 teaspoon of salt.
• To the third cup, add 1 tablespoon of salt.
• Stir each cup with salt thoroughly with a stirring spoon until all salt is dissolved.
• Place each cup in the freezer.
• Write down in your notebook the process you just went through and what you expect to happen with each cup. Consider what you know about salinity and solutions as well as freezing point. Your guess about what will happen is called your hypothesis. The experiment will either prove or disprove your hypothesis.
• After 20 minutes, check each cup to see if any of them have begun to freeze or ice over. Note your observations in your journal.
• Which cup freezes first? Write your observations down.
• Note how long it takes each cup of water to freeze.

The cup with the most salt will freeze the slowest.

Adding a substance to water makes the water denser and thus lowers the freezing point, so the cup with the most salt will freeze the slowest. A heavier liquid has different freezing and boiling points than a liquid without anything added to it.

The experiment should prove that the more salt in the cup, the slower the water freezes but what if you tried different types of liquids or different additives, such as sugar? Repeat the tests and add different things to the water. What do you think will happen? Write down a new hypothesis each time you change the ingredients. How much do you think the results will vary? The only thing you’ll need to watch out for is that no one tries to use those salty ice cubes to make an iced drink. Yuck!

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Hot Ice Science Experiment

You won’t believe how easy it is to whip up this hot ice science experiment! Just like all of our favorite science projects for kids , you just need a few simple supplies from your pantry: vinegar, baking soda and water.

The prep is quick and simple but the results are pure magic! Your kids are going to want to repeat this science experiment over and over again.

Grab 30 easy-to-follow science experiments kids will beg to repeat (plus a no prep science journal to keep track of their results!) in our shop !

Getting Ready

To prep the science experiment, I gathered a few common supplies:

• 4 cups of white vinegar (acetic acid)
• 4 tablespoons of baking soda (sodium bicarbonate)
• A glass measuring cup or mason jar (make sure it’s heat safe glass)

Making Hot Ice

After I collected the supplies, my kids measured 4 cups of vinegar and poured it into a medium-sized pot.

Then they took turns adding 4 tablespoons of baking soda (one tablespoon at a time) to the pot.

The sodium bicarbonate (baking soda) and acetic acid (vinegar) fizzed like crazy forming sodium acetate.

NOTE: The key is to add the baking soda slowly so it doesn’t erupt over the edges of your pot.

Next, we stirred the mixture until all the baking soda dissolved and stopped fizzing.

Then we slowly boiled the solution over medium-low heat for a little over an hour to remove the extra water.

The solution reduced by about 75% so there was just 3/4 cup remaining. I could see white powdery crystals forming on the sides of the pot near the top of the solution when the solution.

NOTE: If you boil your solution at a higher temperature it may turn yellow-brownish but don’t worry, the experiment will still work!

Next, I poured the concentrated sodium acetate into a glass pyrex measuring cup and placed it in the fridge to cool and scraped a little bit of the dried sodium acetate powder off the inside of the pot to use later.

After about 30-45 minutes, the solution was cool enough to turn into ice.

I grabbed my glass dish and placed a small pile of the sodium acetate powder from the pot in the center.  This would act as a seed for the crystals to start forming.

I very carefully took the cooled solution out of the fridge because any bump could start the crystallizing process.

I began pouring the solution very slowly into the pan and crystals began instantly forming.

We all gasped, it was like magic!

As soon as the clear liquid hit the plate white crystals would form like tiny fireworks.  I continued to pour and the liquid crystallized forming a solid as soon as it touched the growing “ice”.

The kids wanted a really tall crystal tower so I poured as slowly as I could.

It kept growing…

and growing.

In the end it was over 6 inches tall!

Of course we all just had to touch it. It was hard like ice but was hot!

NOTE: This form of sodium acetate while non-hazardous can irritate skin and eyes  just like vinegar can.  So be careful when handling the crystal.  Both of my kiddos ended up crumbling the crystal and didn’t have any reaction but I imagine it wouldn’t feel too good if your kiddo had a cut on his/her hands.

Once you are done creating and exploring the crystallized salt you can remelt it to use again and again.

We ended up repeating the experiment a few more times and every time the cooled solution was ready, the kids came running with excitement!

• After explaining nucleation, ask your students if they can think of any other processes that begin with nucleation. (Hint: rock candy, borax crystals, clouds and carbon dioxide bubbles in soda.)
• Ask students if they can think of other reactions that release heat like hand warmers and burning candles.
• Try adding a drop of food coloring to see if you can make colored crystals.

The Science Behind Hot Ice

The sodium acetate solution in the refrigerator is what is called a supercooled liquid .  That means the sodium acetate is in liquid form below its usual melting point.

Once you touch, bump, or add a small crystal that is not liquid, crystallization will begin and the liquid will change to a solid.

When the molecules in the solute (sodium acetate) are in a solution, they normally are surrounded by a solvent (in this case water molecules).

Occasionally, a few solute molecules will bump into each other and stick together for a little while but they will eventually break apart.

If enough solute molecules stick together, they can overcome the forces in the solvent that would normally break the solute molecules apart.

When that happens, the clump of solute molecules serves as a seed (or nucleation site) for other solute molecules to cling to so the crystallization process can take off again.

The sodium acetate powder we placed on the plate acted as a nucleation site for the dissolved sodium acetate in the solutions.

The crystallizing sodium acetate releases energy in the form of heat and is an example of an exothermic process. Sodium acetate is often used in hand warmers as it release heat when crystallizing!

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An ancient and impure frozen ocean on Ceres implied by its ice-rich crust

• I. F. Pamerleau   ORCID: orcid.org/0009-0008-9473-3147 1 ,
• M. M. Sori   ORCID: orcid.org/0000-0002-6191-2447 1 &
• J. E. C. Scully   ORCID: orcid.org/0000-0001-7139-8050 2  

Nature Astronomy ( 2024 ) Cite this article

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• Asteroids, comets and Kuiper belt
• Geodynamics

Ceres is a key object in understanding the evolution of small bodies and is the only dwarf planet to have been orbited by a spacecraft, NASA’s Dawn mission. Dawn data paint an inconclusive picture of Ceres’ internal structure, composition and evolutionary pathway: crater morphology and gravity inversions suggest an ice-rich interior, while a lack of extensive crater relaxation argues for low ice content. Here we resolve this discrepancy by applying an ice rheology that includes effects of impurities on grain boundary sliding to finite element method simulations of Cerean craters. We show that Ceres can maintain its cratered topography while also having an ice-rich crust. Our simulations show that a crust with ~90% ice near the surface, which gradually decreases to 0% at 117 km depth, simultaneously matches the observed lack of crater relaxation, observed crater morphology and gravity inversions. This crustal structure results from a frozen ocean that became more impurity rich as it solidified top-down. Therefore, the Dawn data are consistent with an icy Ceres that evolved through freezing of an ancient, impure ocean.

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Dwarf planet Ceres is thought to have a high ice content compared with other objects in the inner solar system 1 , 2 . Constraining the composition of Ceres’ interior helps to elucidate its internal processes, differentiation state and potential habitability. Although ice is unstable on the surface of Ceres owing to its proximity to the Sun, hydrated minerals were spectroscopically observed on the dwarf planet’s surface before the arrival of the National Aeronautics and Space Administration (NASA)’s Dawn mission 3 . It was thought that these hydrates would act as an insulating regolith for an extremely ice-rich crust below, which was suggested from pre-Dawn density measurements 4 . Because of these observations and the inferred crustal composition, it was predicted that Ceres would be unable to support topography if it was fully differentiated with complete ice–rock separation 5 . These models suggested that craters on an icy Ceres would efficiently viscously relax away over geologic time.

When Dawn arrived at Ceres, some data were consistent with the hypothesis that the body contains an ice-rich crust, and some data were not. Gravity inversions 6 implied an average crustal density (1,287 kg m −3 ) very near that of water ice, and nuclear spectroscopy revealed high amounts of hydrogen in the upper metre, which is consistent with expansive water ice below the regolith 7 . Additionally, the simple-complex transition diameter of Cerean craters places it along the trend of other icy bodies 8 , suggesting that craters form as if in an ice-rich crust. There have also been many geomorphologic observations that support the presence of subsurface ice 9 . However, it has been argued that the heavily cratered landscape revealed by Dawn on Ceres today is inconsistent with an icy internal structure 10 . Numerical modelling suggested that the lack of extensive crater relaxation implied Ceres’ crust has no more than 40% ice volumetrically 11 . Therefore, the current accepted interior structure invokes weak differentiation, with a crustal composition that is less than 40% ice, with silicates, salts, organic material and clathrates making up the rest of the material 11 , 12 .

Although consistent with unrelaxed craters, there are potential issues with an ice-poor, weakly differentiated Ceres. This structure relies on the idea that even a low ice content will allow craters to form in the same manner they do in extremely ice-rich bodies like the icy Galilean satellites, but it is unknown how low the ice content can be for this to still hold true. Additionally, the current model invokes clathrates, a light but strong material formed when gas is trapped in an ice lattice. Clathrates were thought to be necessary to account for the lack of relaxation and low density of the crust, but it is uncertain if they would form on Ceres based on thermochemical models 12 . Moreover, clathrates may be unstable in the presence of salts 13 , which are abundant on Ceres: brines at depth that have erupted onto the surface have been proposed as the source of the faculae in Occator crater 14 , 15 , 16 and the cryovolcanic construct Ahuna Mons 17 . Lastly, it is unknown if an interior structure for Ceres with only weak differentiation between ice and rock is realistic 10 , 18 . Ceres’ crust may have formed from a freezing ocean 12 , 19 , 20 , 21 , and thermal models have suggested that efficient separation of water and silicates would have occurred early in Ceres’ history 1 , 4 , 22 , leading to a strongly differentiated interior. Ice shells on other ocean worlds are thought to be extremely ice rich, like on Europa and Enceladus. Callisto has been proposed to only be partly differentiated 23 with a subsurface ocean 24 , but other work has argued that, like Ceres, an undifferentiated or only partially differentiated Callisto would be very surprising on theoretical grounds 25 . Note that we use ‘differentiation’ in this Article to refer to separation of rock and water ice and does not necessarily include metal.

We propose that an ice-rich crust that is mechanically strong fits Dawn data and numerical models of Ceres’ thermal evolution. Rheologic experiments conducted after Dawn’s arrival at Ceres have shown that ice can behave much more rigidly on geologic timescales than previously thought with only a small (≥6%) impurity content 26 , 27 . This more rigid ice rheology is highly relevant to Ceres given that the gravity inversions are consistent with an icy crust with minor impurity content. However, this rheology has not yet been applied to Ceres. We hypothesize that, when this rheology is considered, Ceres can maintain its cratered landscape even with an icy crust and differentiated interior. A mechanically strong, icy crust would fit the Dawn data without invoking clathrates or the low-ice crater formation theory. While this is a ‘simpler’ way to reconcile Ceres’ low-density crust and cratered landscape, it does not exclude the structure currently in the literature 10 , 11 , 12 .

We tested our hypothesis by simulating relaxing Cerean craters using a finite element method (FEM) model. We used COMSOL Multiphysics software to construct our model and assessed the interior structures that could allow craters to be maintained. Viscoelastic relaxation is dependent on three main parameters in our model: crater diameter (large craters relax faster than small ones), latitude (a proxy for temperature, which strongly affects rheology) and crustal ice content (icier materials relax faster than drier materials). The annual-average temperature is calculated to be ~156 K at the equator and ~90 K at the poles 28 . We seek to maximize the ice content while minimizing relaxation because, other than the lack of widespread relaxation 10 , 11 , the Dawn data suggest an icy crust 6 , 7 , 8 , 9 . More details about the FEM model can be found in Methods.

We tested three basic crustal structures in our FEM simulations to assess which structures could maintain craters and be consistent with the heavily cratered landscape observed by Dawn. The first structure is a uniform crust, such that ice and impurity content are uniform throughout space for each simulation (Fig. 1a ). A uniform crustal structure could be a result of a partially differentiated Ceres that did not fully separate the rock and ice material, either due to a strong, undifferentiated crust that received little accretional heat 19 or a frozen ocean rich in fines 20 , 21 . The second internal structure we investigated was a two-layer crust (Fig. 1b ). The layers are of uniform compositions, and the less dense layer (that is, with a higher ice content and weaker rheology) is on top of a denser, drier layer. A two-layer model does not fit a proposed internal evolution pathway for Ceres but serves as a useful conceptual example to help us understand how discrete changes in the distribution of impurities affect relaxation. Larger craters are more sensitive to material deeper in the interior. Therefore, higher impurity content with depth may help to slow down relaxation of larger craters relative to the uniform case. For both this and the first crustal scenarios, the total crustal thickness 6 is 40 km. Lastly, we tested a gradational crustal structure on Ceres, where the shallow subsurface has a high ice content that gradually decreases with depth as impurity content increases (Fig. 1c ). Like the two-layer scenario, this structure has more impurities with depth, impeding relaxation of large craters. Our nominal structure for this scenario contains 90% ice near the surface and linearly decreases to 0% ice at 117 km depth. This structure yields an average density of the top 41 km that matches gravity inversions 6 . We note that other surface ice contents and impurity gradients can be chosen to be consistent with Dawn data, given the uncertainty in the gravity inversions and the densities of the impurities. This gradational internal structure could be the result of a top-down ancient frozen ocean on Ceres that contained impurities over a range of grain sizes. In this scenario, fine-grained impurities were trapped between the ice grains 12 , 20 as freezing progressed, while slightly larger grains remained below the freezing front, which led to an ocean that became more impurity rich with time and depth. This would result in a crust that becomes denser with depth, consistent with gravity measurements made by the Dawn spacecraft 29 .

a , A uniform crust, 40 km thick. b , A two-layer crust, where the top layer is icier than the bottom layer. Each layer is 20 km in our simulations. c , The gradational crust, in which the ice content decreases linearly with depth. The uniform crust in a would need to be more impurity rich than the top layer and more ice-rich than the bottom layer of b for both scenarios to match Dawn gravity inversions. The composition gradient in c depends on the ice content in the near subsurface to match gravity inversions.

Our model predicts negligible crater relaxation for much of the parameter space, regardless of the simulated crustal structure. For all crustal structures, simple craters (≤12 km in diameter) are retained ubiquitously under all conditions as long as ≥6% impurities exist. For example, a 12-km-diameter crater at the warm equator in a crust that is uniformly 90% ice relaxes by <5% (see Methods for the definition of ‘per cent relaxation’) after 1 Gyr (Fig. 2 ). Simple craters at other latitudes, in crusts of lower ice content, or of smaller diameter relax even less. These findings are a major divergence from previous work, which argued that even simple craters on Ceres would relax away in an ice-rich crust 5 , 11 .

This simulation was run in a uniformly 90% ice crust (Fig. 1a ) at the equator and shows total vertical displacement after 1 Gyr of relaxation. The black lines are the initial state of the simulation, and the solid colour shows the final state of the simulation. In this case, the crater has only shallowed by ~70 m from an initial depth of 2,400 m (seen as the solid colour at the centre of the crater slightly offset from the black line), for a relaxation percentage of <4%.

The relaxation of complex craters is dependent on free parameters and assumed crustal structure. Complex craters ≤40 km in diameter experience little deformation on Gyr timescales in the cold temperatures of the mid- or high latitudes in ice-rich crusts (Fig. 3 ). However, large complex craters at the warm, equatorial latitudes experience substantial amounts of relaxation for some crustal structures. A uniform-composition crust allows ~30% relaxation at the equator for 40-km-diameter craters in a 90% ice crust (Fig. 3a ). Increasing impurity content will hinder relaxation but also could increase the crustal density to a value inconsistent with gravity inversions if the impurities are in the form of dense silicates. The two-layer crustal structure yields similar results to the uniform crust case because craters are most sensitive to the top layer’s composition even for our largest simulated craters. Holding the ice content of the top layer constant and varying the ice content of the bottom layer yields nearly identical relaxation states. The two-layer scenario yields slightly lower relaxation percentages compared with the uniform crust case for larger craters, which are relatively more sensitive to the deeper layer composition (Fig. 3a,b ). The last scenario, a crust nominally with 90% ice near the surface and becoming gradually more impurity rich with depth, yields substantially less relaxation for large craters compared with a uniform or two-layer crust. Complex craters between 12 and 40 km in diameter relax by <20% after 1 Gyr depending on latitude and crater size (Fig. 3c ). As is the case with the other simulated crustal structures, the higher the impurity content, the less relaxation is allowed, but the density profile is also changed. Displacement and per cent relaxation values of our simulations in Fig. 3 can be found in Supplementary Data 1 .

a , A uniform crust with ~90% ice content, 40 km thick (Fig. 1a ). b , A two-layer crust, where a ~90% ice layer overlies a ~63% ice layer, both 20 km thick (Fig. 1b ). c , A gradational crust, with ~90% ice in the near subsurface and ~40% ice at 65 km depth, the bottom of the simulated crust (Fig. 1c ). A 40 km crater at the equator (purple, solid line) experiences the least amount of relaxation (~20%) in this crustal structure.

All crustal structures we tested yield substantially less relaxation of craters on Ceres than previously thought possible in an ice-rich crust, as long as a few per cent or more of impurities are present. This result occurs because impurities effectively prevent grain boundary sliding (GBS) 26 , a major deformation mechanism of ice on Ceres at the relevant temporal and spatial scales. The distribution and quantity of these impurities can help to minimize relaxation of large, equatorial craters, which will help determine our favoured crustal structure. A uniform crust with a high ice content (90%) is able to retain craters throughout most of the parameter space (that is, crater diameter and latitude). Simple craters and small complex craters will never relax on Ceres as long as a few per cent or more of impurities are present, as the largest simple crater in the warmest plausible temperature experiences <5% relaxation after 1 Gyr (Fig. 2 ). However, a uniformly icy crust allows more relaxation of large, equatorial craters than is observed on Ceres. Increasing impurity content will slow down relaxation to better fit observed Cerean craters (for example, Supplementary Data 2 ), but with too high of an impurity content, the crustal structure would not fit gravity data 6 . The simulated uniform crust that most closely matches gravity inverted density measurements (~75% ice) yields 23% relaxation for a 40 km crater at the equator (Supplementary Data 2 ). Although a uniform crustal structure does not perfectly match the observations of the cratered terrain on Ceres, it allows for an ice-rich crust that retains topography more efficiently than previously thought 5 , 10 , 11 . The two-layer model simulations do not fit the Dawn data as well as the uniform crust. Two-layer simulations perform slightly better (that is, have lower per cent relaxations) than uniform simulations when the top layer and uniform crust share the same composition. However, this small improvement in matching the observed rheology is outweighed by the large increase in density from the lower, more impurity-rich layer. Increasing the impurity content of a uniform crust will cause less relaxation to occur than keeping the impurity content fixed and adding a higher impurity second layer. Therefore, a uniform crustal structure should fit both the lack of extensive crater relaxation 10 , 11 and density profile 6 measured from the Dawn mission better than a two-layer model.

We argue that a crust with high ice content at the surface that grades into lower ice content at depth best matches Dawn observations (Fig. 1c ). Our preferred model has an extremely ice-rich near subsurface at 90% and linearly decreases in ice content until it reaches 0% ice at 117 km depth. This crustal structure minimizes crater relaxation (Fig. 3 ) and is consistent with Ceres’ cratered landscape 8 , crater morphologies 8 , high hydrogen content in the shallow subsurface 7 , icy geomorphology 9 and increasing density with depth 29 , all without invoking clathrates. This gradational structure also allows for enough water ice at depth to create the brines hypothesized to form the bright faculae in Occator crater, which probably require endogenic H 2 O (refs. 14 , 15 ). We tested other uniform and gradational ice/impurity contents (with greater fractions of impurities) and found that it takes a substantial increase in impurity content to reduce relaxation by <10% (see Supplementary Data 2 for examples). As this dramatic increase in higher density impurities does not match gravity inversions and only slightly minimizes the relaxation, we favour a crustal composition of 90% ice at the surface and 0% ice at 117 km depth because these values match gravity inversions that suggest an average density 6 in the upper 41 km of 1,287 kg m −3 .

Fine-grained impurities need to be trapped at the ice grain boundaries to inhibit GBS 26 and make ice sufficiently resistant to relaxation over long timescales, ruling out a scenario of a pure ice crust. Soluble impurities such as salts and carbonates are viable candidates to freeze out with the ice 12 and increase the crust’s strength. Colloidal solutions (fine, insoluble particles suspended in solution) have been suggested to help trap impurities in a fine-rich fluid 30 , 31 , which has been proposed to account for the impurities in Ceres’ ancient ocean 20 . Experimental data suggest that lenses of fine-grained impurities and ice may occur on Earth, as the trapping of impurities between ice grains has been observed in terrestrial lake settings 32 and Antarctic ice 33 , and the same thing very well may have occurred on Ceres. Both soluble impurities and suspended colloidal solutions may work in tandem to help trap impurities between ice grains and increase the strength of Ceres’ crust, as we simulate in our models.

These different crustal structures may reflect different evolutionary pathways for Ceres and its ancient ocean. There are four main proposed internal structures for Ceres. The first is an undifferentiated body 34 with no melting of water ice. The second is a partially differentiated three-layer Ceres with an undifferentiated crust being maintained over a warmer, differentiated mantle and core 19 . Both of these cases are represented by our uniform crustal scenario (Fig. 1a ) and are not favoured. The other two evolutionary pathway involve full melting of the water ice, leading to a mudball Ceres 19 , 20 , 21 or a brine-rich Ceres. In the mudball theory, the accreted, undifferentiated ice melts from the inside out owing to short-term radiogenic heating and leaves an ocean rich with suspended fine-grained particles. In this ‘muddy ocean’, larger clasts (≥mm) will sink rather quickly through the ocean to form a rocky core, but fines (<μm) will be suspended over long periods of time, if not indefinitely 20 , 21 . As the muddy ocean freezes top-down, the fines are trapped in the forming crust. In the brine-rich theory, a freezing ocean may form with increasing impurities (be it salts, clathrates or suspended particles) with depth 12 , which matches gravity inversions from Dawn’s second extended mission suggesting an increasing density with depth 29 . A leftover brine layer may be present in this pathway, and the core could contain both water ice and rock. The main difference between the mudball theory and the brine-rich Ceres is the lack of a brine-rich layer between the crust and core in a mudball Ceres, as well as a purely rocky core in the mudball and a water/rock core in the brine-rich Ceres. Note that while increasing impurities with depth explains the Dawn gravity inversions 29 , decreasing porosity in a uniform crust would also explain this observation. Our gradational crustal structure agrees with the top-down freezing ocean model and the observed density profile. Regardless of the mechanism of crustal formation, our results show that either method can allow more ice than previously thought, making Ceres more similar to other ocean worlds with ice-rich shells.

Our results imply that previous geophysical studies of Ceres may need to be revisited with the interior structure that we favour, an ice-rich compositionally gradient crust, in mind. Previous work suggested that Dawn data allow Ceres to be only weakly 10 , 18 or even not differentiated at all 34 based on topographic support arguments. However, our proposed interior structure with a strong, impure-ice crust implies efficient separation of water from silicates that later formed a compositional gradient because of top-down freezing. This is consistent with thermal evolution models that predict water–silicate separation on Ceres is efficient and inevitable 22 . Deformation models of mounds that may have formed cryovolcanically 28 , 35 or from solid-state flow 36 may overestimate their formation rates if the material comprising these features has ≥6% impurity content.

We simulated craters up to 40 km in diameter because they have been efficiently retained on Ceres. Craters larger than this tend to have more complicated morphologies 8 that are asymmetric. Additionally, we observed subtle signs of relaxation for Cerean craters in the 50–100 km range (Supplementary Fig. 1 and Supplementary Section I ). As the nature of this relaxation is asymmetric, it is not appropriate to simulate their deformation in our two-dimensional (2D) axisymmetric models. While we do not simulate larger craters in this work, our gradational crust will help minimize their relaxation because bigger craters will be more sensitive to deeper, more impurity-rich material. Further, some of the largest craters on Ceres cited with deep floors (>4 km) indicating little to no relaxation has occurred (for example, Vinotonus, Ezinu, Urvara and Yalode) are found at mid-latitudes (~45°) 8 , where our simulations show relaxation will be ineffective regardless of crater diameter because of cold surface temperatures (Fig. 3 ). For craters >100 km, there is evidence that substantial relaxation has occurred from the dearth of large craters 37 and topographic power spectra 6 . Impact and relaxation simulations focused on planetary-scale basins could further help elucidate the evolutionary pathway of Ceres’ ancient ocean.

Our proposed interior structure and evolutionary pathway for Ceres has implications for future spacecraft missions and can be tested by those missions. As a relic ocean world in the inner solar system, Ceres is often treated as an accessible analogue to other, more traditional ocean worlds 38 , 39 (for example, the icy Galilean moons). If the ancient ocean froze out to form a crust with a high ice content, it is possible that Ceres is less of an outlier and more akin to other ocean worlds than previously thought. Future mission concepts 40 could test this idea by inferring the compositional structure of the upper few kilometres with geophysical methods or constraining Ceres’ thermal evolution through returned sample analysis. Ground-penetrating radar may help determine the ice content of Ceres’ crust and any lateral and vertical variability, which would elucidate which crustal model best agrees with Ceres’ interior. Additional key objectives of a future mission to Ceres, such as identifying the rock–ocean interface where brines are present 40 , may need to be reassessed with our proposed interior structure in mind. In our model, the interface between the base of the crust–ice shell and any remnant brines may be deeper than in current models 6 .

We use the FEM software COMSOL Multiphysics to run our viscoelastic simulations. We use the thermal physics module to set up a temperature profile through the interior and the solid mechanics module to simulate relaxation.

We simulated three crustal structures in this work: a uniform, 40-km-thick crust (90% ice in Fig. 3a ); a two-layer crust, where each layer is 20 km thick and has a uniform composition (90% and 63% ice for the top and bottom layer in Fig. 3b , respectively); and a gradational crust that decreases in ice content with depth. We propose a gradient that consists of 90% ice at the near subsurface, linearly grading to 0% ice at 117 km depth (Fig. 3c ). We only simulate this crust to a depth of 65 km (Fig. 1c ) as the material below that will have <40% ice and deformation will be effectively inhibited 11 . We favour the gradational crust as it best fits Dawn data of all our simulations (see Discussion for more details). However, we only use ice and hydrated silicates in the composition of our simulations, and the values for these crustal structures have some flexibility based on this assumption. We also simulated other, more impurity-rich compositions for these three scenarios, which are reported in Supplementary Data 2 .

We construct our simulations to be realistic while being computationally inexpensive. We model simple craters (≤12 km in diameter) with a parabolic bowl shape geometry 41 . The floor elevation is one-fifth the diameter below the surrounding terrain. A topographic profile of a young Cerean crater is used for the complex crater simulations and is taken from Dawn observations. The topography is of a 40 km crater and used unaltered for our 40 km simulations, but we scale it on the basis of the depth-diameter ratios reported in ref. 8 for our 20 km simulation. Figure 2 shows a detail of a portion of a 12-km-diameter crater simulation, but the actual model domain for each simulation continues radially outwards to minimize effects from the lateral boundaries on the crater (for three and six crater diameters from the centre of the crater for complex and simple craters, respectively). The crust extends to a depth of 40 km for the uniform and two-layer crustal structures (Fig. 1a,b ), as suggested by gravity data 6 , or 65 km for the gradational crust case (Fig. 1c ), below which the crust has low enough ice content such that it only deforms in a rocky manner 11 .

The simulations are 2D axisymmetric, as the craters we simulate in this work are largely radially symmetric. This geometry assumes that any features that are not radially symmetric in these craters are not big enough to affect the viscoelastic relaxation of the overall crater. This would not be the case for craters >40 km, which show features sure as fractured floors, central pits and so on 8 that would need to be simulated in a thee-dimensional asymmetric simulation. The mesh is designed to be finer near the crater, where deformation is maximized, than elsewhere in the domain. We tested a few cases and found that our results do not notably change by increasing the resolution of the mesh compared with the simulations presented here.

Thermal model

As the rheology of the simulated material is highly dependent on temperature, we calculate an initial thermal profile through the interior before allowing deformation. The model uses the geothermal heat flow, surface temperature and thermal material properties to calculate temperature through the crust. The heat flow is taken to be 1 mW m −2 , but we note that increasing the value to 3 mW m −2 did not substantially affect our results. The temperature boundary condition at the top is the annual-average surface temperature, justified by the fact that the thermal skin depth is orders of magnitude smaller than the crustal thickness. That surface temperature is latitudinally dependent and taken from a previous thermal model 28 , which assumes an emissivity of 0.9. We calculate the surface temperature every 5° latitude to apply a thermal boundary condition to our simulations. The surface temperature at the equator is estimated to be ~156 K, while the surface temperature at the poles is estimated to be ~90 K. We assume a thermal conductivity equation for all simulations that is a linearly weighted mixture of ice and impurities, depending on temperature and the impurity content in that simulation. Therefore, a uniform crust will have a thermal conductivity that is only temperature dependent for each simulation, and similarly for each layer in the two-layer model. The gradational crust will have a thermal conductivity that depends on both temperature and composition, as temperature and impurity content change with depth. Ice has a temperature-dependent thermal conductivity 42 of 651 W m −1   T −1 , where T is temperature in Kelvin, and the impurities have thermal conductivity 43 of 2 W m −1  K −1 . We note that, while the thermal conductivity depends on the impurity content (which varies with depth for the gradational scenario), the thermal gradient through all simulated crusts differs by only a few Kelvin owing to Ceres’ low heat flow. For example, the temperature at 40 km depth below the equator is 166, 167 and 168 K for each crustal structure from Fig. 3 , respectively. We do not account for insulating regolith, which may allow a few more Kelvin in the near subsurface.

Viscoelastic relaxation

Our simulations include both elastic and viscous deformation. Elastic deformation in our model is controlled by Young’s modulus and Poisson’s ratio, assumed to be 10 10  Pa and 0.25, respectively. Elastic deformation is small on geological timescales; our results are not sensitive to small changes in the elastic parameters.

Viscous deformation is the dominant control on whether craters are maintained over geological timescales. For the viscous creep physics, we solve the Stokes equations for conservation of mass and momentum, respectively:

where u is the velocity vector, σ is the Cauchy stress tensor, \(\rho\) is the density (917 kg m −3 for ice, 2,500 kg m −3 for impurities) and g is the acceleration due to gravity vector (0.27 m s −2 on Ceres).

Viscous relaxation of craters in an icy material is driven by several deformation mechanisms. At the stresses and timescales relevant to kilometre-scale or larger topography on Ceres 35 , the two important mechanisms are dislocation creep 44 and GBS 45 , given by the following two equations, respectively:

where \(\dot{\varepsilon }\) is the strain rate, \(\tau\) is the deviatoric stress in MPa, \(\varphi\) is the fractional impurity content, T is the temperature in Kelvin, R is the gas constant and d is the grain size in metres. Note that the addition of particulates into an ice mass is accounted for with a factor of e (− bφ ) where b is a constant, b  =  2 . This factor also has a power relation (for example, ref. 11 ), leading to the e (−8 φ ) factor in equation ( 3 ). COMSOL describes deviatoric stress with the von Mises equivalent stress, which is volume preserving and is adjusted for the uniaxial strain conditions in which these values were experimentally derived. These temperature-, stress- and composition-dependent rheology equations are applied throughout all simulations, but with an impurity content of ≥6% (ref. 26 ), GBS is made ineffective 26 , leaving dislocation creep as the important deformation mechanism. Dislocation creep is grain size independent 45 , and so we do not assume a particular grain size. GBS would be the dominant deformation mechanism for the Cerean craters in pure ice, so without it, a crust with ≥6% impurities is much stronger than previously modelled. Other equations for strain rates of these deformation mechanisms have been proposed 45 and may result in slightly different strain rate values.

At the end of the simulations (1 Gyr of deformation), we calculate the per cent relaxation of the crater. We define ‘per cent relaxation’ as the ratio of the difference in elevation between the crater rim and floor at the beginning and end of the simulation, where 0% reflects no change in elevation. For simple craters, we define the floor elevation as the centre of the crater, which is one-fifth the diameter of the crater. Complex craters have relatively flat floors, but for the topographic profiles we used in our simulations, there is a slight slope down towards the centre of the crater. We define the floor elevation of the complex craters as the elevation where the relatively flat floor and peak meet, which is the deepest part of the crater. We note that the floor elevation is the deepest part of the crater in each simulation, and because of this, will have the highest stresses (and displacement).

The surface of the model, including the crater and surrounding terrain, is set to be a free surface. The bottom surface is fixed, and the wall that is not being rotated around (to make the model 2D axisymmetric) is allowed to deform in the z direction but not the r direction.

Data availability

Data from NASA’s Dawn mission are available to the public in the NASA Planetary Data System’s small bodies node ( https://pds-smallbodies.astro.umd.edu/ ).

Code availability

The code used to simulate relaxing craters is available on Figshare at https://figshare.com/projects/An_ancient_and_impure_frozen_ocean_on_Ceres_implied_by_its_ice-rich_crust/210268 . The code was made in the COMOSL Multiphysics Software and requires a licence for the software, as well as the Solid Mechanics and Nonlinear Materials modules.

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Acknowledgements

This work was funded by NASA Discovery Data Analysis Program (DDAP) grant 80NSSC22K1062, which was received by all authors.

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Supplementary Fig. 1 and discussion.

Supplementary Data 1 and 2

Supplementary Data 1. Data of runs reported in Fig. 3. Crater diameter and depth are reported in kilometres, but displacement from relaxation is reported in metres. See Methods for definition of ‘floor’ for simple and complex craters as well as ‘per cent relaxation’. The location for ‘rim displacement’ was taken from the peak of the rim. Supplementary Data 2. Data of runs not included in Fig. 3. See Supplementary Data 1 caption for additional information.

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Pamerleau, I.F., Sori, M.M. & Scully, J.E.C. An ancient and impure frozen ocean on Ceres implied by its ice-rich crust. Nat Astron (2024). https://doi.org/10.1038/s41550-024-02350-4

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DOI : https://doi.org/10.1038/s41550-024-02350-4

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