Science Experiments at Home: The Edible Solar System
Why is Neptune blue? Is Saturn the only planet with rings? How many Earths could you fit inside Jupiter? Here is an easy, flexible activity you can do to introduce size scales and cool planet facts for the planets in our solar system … and have a snack at the end!
Sabrina Stierwalt, PhD
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Science Experiments at Home: The Edible Solar System
I often get asked for ideas for easy, astronomy-related activities that can be done with kids, and one of my favorites is the edible solar system. It’s easy to set up—you just need one trip to the grocery store beforehand so it can be done on relatively short notice. It works for most age groups since you can vary the level of the material you present. It can also be done with any number of kids, whether you are just at home with your family or entertaining a classroom full of children. I once did it with only 24 hours notice with 600 children (!) at a primary school outside of Cape Town, South Africa, so almost anything is possible with this activity.
The goal of the activity is to introduce kids to the size scales of planets in our solar system as well as share some cool science facts about each planet. You can do this in a fairly straightforward way by bringing in different foods (usually fruits) that show the relative size scale of the planets. The Sun is too big so I usually use a comparison in the room. For example, you can set up the activity with: “If we could shrink down the Sun so that it were as big as that wall, let’s see how big each of the planets would be.” One fun way to keep your audience involved is to pull your edible planets out of a bag one by one (possibly in order of distance from the Sun) and ask everyone to guess which planet that food represents.
As you pull out each “planet,” you can highlight cool science facts about them. This activity is extremely flexible since you can vary the level of the information you present based on your crowd. I suggest not pitching too low however: kids start learning/reading/hearing about the planets pretty early on, so I’m often amazed by how much they know.
Preparing the Activity
If you prefer to use nonedible items to represent your planets, balls obviously work well, from the large bouncy balls used for balance in some exercise classes to basketballs to marbles. If you choose to go the edible route, there are many suggestions online of the varieties of foods you can use with to-scale sizes already calculated. I am a big fan of not reproducing hard work that someone has already done, although it’s always good to check a few of the relative sizes to make sure they were calculated correctly.
My planetary edibles of choice are usually fruits, so below I give suggestions for what types of fruit to use, as well as a few interesting facts, for each planet in our solar system. The relative sizes that I suggest all assume that the Sun is roughly 17.5 feet tall, but you can scale up or down depending on the items you would like to use – just be sure to scale everything by the same amount.
Cool Planet Facts
Mercury (a pomegranate or other seed): Mercury is the closest planet to the Sun and the smallest. The planet has no atmosphere and so is very hot during the day but very cold at night. These extreme temperatures make sending probes there to learn more about the planet very difficult. The surface is also cratered like the surface of our Moon possibly because Mercury itself has no Moon to protect it from the onslaught of space debris. On Mercury, a day is longer than a year because it takes longer for the planet to completely rotate on its own axis than it does for the planet to make one lap around the Sun.
Venus (a cherry tomato): The atmosphere on Venus is an example of what the greenhouse effect can do when left to run rampant. The atmosphere is thick with carbon dioxide so not much sunlight reaches the surface. The light that does reach the surface gets trapped causing the temperature to rise so high that Venus is actually hotter than Mercury despite being farther from the Sun. When visible, Venus is the third bright object in the sky (after the Sun and the Moon).
Humans are able to thrive here due largely in part to the existence of liquid water: roughly 70% of the Earth’s surface is covered by water.
Earth (a cherry tomato): Asking your audience what makes the Earth different from all of the other planets can lead to some amusing answers—of course, it’s us! Humans are able to thrive here due largely in part to the existence of liquid water: roughly 70% of the Earth’s surface is covered by water. We have one Moon which is the farthest any human has ever traveled. Using the same fruit for Venus and Earth highlights that they are very similar in size despite all of their other differences.
Mars (a blueberry or blackberry half the size of your cherry tomatoes): Recent results from NASA show evidence of liquid water on the surface of Mars and there are currently three rovers visiting the planet (Spirit, Opportunity, and Curiosity). The surface of Mars is very dynamic due to its powerful dust storms. (Remember that’s how Matt Damon got trapped there at the beginning of The Martian!) Mars is called the Red Planet because its surface is covered in a rust-like dust. The Red Planet is home to Olympus Mons, the largest volcano in the solar system at 21 kilometers high and 600 kilometers across. Mars is relatively cold in part because it has no atmosphere to trap in heat.
Jupiter (large watermelon roughly ten times the size of your cherry tomato): Jupiter is the largest planet in our solar system (> 1300 Earths would fit inside it) and has at least 63 known moons, four of which are bigger than Pluto. Jupiter is the fourth brightest object in the sky and is more than twice as massive than all of the other planets combined. In fact, if Jupiter were just 80 times more massive than it is, it would have been able to ignite hydrogen fusion turning it into a star like our Sun, rather than a planet.
Saturn (large grapefruit or melon slightly smaller than your watermelon): Saturn is the second largest planet in our solar system after Jupiter and is known for its stunning ring system. The rings are made up of millions of ice crystals, some as big as houses and others similar to small specs of dust. Saturn is large but not very dense so if you could fit it in your bathtub, the planet would float.
Uranus (apple, lime, or mango roughly four times the size of your cherry tomato): Astronomers suspect that Uranus suffered a major collision during its formation because the planet actually lies on its side as it travels in its orbit. (In astronomy speak, its spin axis is nearly parallel to the ecliptic,) Uranus is a beautiful blue color due to the methane in its atmosphere. Rumor has it that William Herschel, the British discoverer of Uranus, almost named the planet “George” after King George III.
Neptune (same fruit as Uranus): Neptune hosts some of the most violent weather in our solar system with strong winds and intense storms. The existence of Neptune was predicted based on unexplained wobbles in the orbit of Uranus. Like Uranus, Neptune is also a beautiful blue color, and its hue led to the decision to name the planet after the god of the sea. At one point Neptune had a large dark spot but it later disappeared for mysterious reasons. Neptune also has a ring system, but it is smaller and fainter than those circling Saturn. Just as with Earth and Venus, using the same fruit for Neptune and Uranus highlights that they are very similar in size despite all of their other differences.
Extending the Activity
If you have a large enough group, you can ask for volunteers to represent each planet and have them stand at distances from the Sun that are also to scale. This really drives home just how empty space really is. Even if you are in a large classroom or a gymnasium, poor Neptune will be all the way down the hall!
To help your audience remember facts about each planet, you can also provide props to your planet volunteers that highlight something you have discussed about each of them. For example, Mercury wears sunglasses because it is closest to the Sun, Venus wears a blanket to represent its thick atmosphere, and Earth holds a bottle of liquid water. Mars stands on a chair (to represent being home to the tallest volcano in the solar system) and Jupiter holds a flashlight with no batteries (to represent its status as a failed star). Saturn holds a hula hoop to represent its rings, Uranus holds a pillow because the planet rests on its side, and Neptune wears bangle bracelets since the planet also hosts a ring system.
Have fun setting up your edible model of our solar system, and don’t forget to enjoy a planetary snack when you’re done!
Until next time, this is Sabrina Stierwalt with Ask Science’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Ask Science on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.comcreate new email.
Image courtesy of nasa.gov
