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8 Planets Density Experiment

Today we start the final week of Story Book Summer with one of my favourite themes – SPACE. Welcoming to Rainy Day Mum we have Carla from Preschool Powol Packets sharing a Science Experiment based on the book There’s No Place Like Space.

Hi Rainy Day Mum and friends!  I’m Carla from Preschool Powol Packets, and I am super excited to be sharing one of our favorite space-themed books and a preschool science experiment to go with it!

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We absolutely love There’s No Place Like Space by Tish Rabe.  The language is lively and fun, the pictures are fabulous, and (the kids’ favorite part) the entire book is a journey through the solar system led by the famous Cat in the Hat.

There’s No Place Like Space! All About Our Solar System (The Cat in the Hat’s Learning Library)
  • Hardcover Book
  • Rabe, Tish (Author)
  • English (Publication Language)
  • 48 Pages – 10/26/1999 (Publication Date) – Random House Books for Young Readers (Publisher)

One of the lesser-known facts that it mentions is that Saturn could float in an ocean, “and not even sink!”  While there may be some technical exceptions to this (see my Special Note at the bottom), the idea that planets have different characteristics, densities, and behave differently is an important one.  And, it leads us to our experiment: 8 Planets Experiment!

8 Planets Experiment

Materials Needed:

* 7 rocks and 1 foam ball or wooden ball
* paint and paint brushes
* bowl of water (best outside!)
*other objects for children to test

Step by Step:

This activity has two parts: making the planets and testing them to see which float.  Children love painting rocks and foam balls!  But, if you don’t have the materials or you prefer not to paint, you can simply use fruits, vegetables, and rocks to represent the planets.  We’re going to continue as though everyone wants to paint!

Child painting

1.  Make the planets with your children by painting the rocks!  Use No Place Like Space to get ideas for the colors of the planets, and make sure Mercury, Venus, Earth, and Mars are smaller than Jupiter, Uranus, and Neptune.  Saturn should be made from the foam or wooden ball so it will float, while the other planets should all be made from rocks (or other objects that will sink).  Let your planets dry, and then move on to Step #2.

Child holding painted rocks
child painting a rock blue
Different coloured painted rocks on a paper with a green child's handprint.

After we made the planets in our solar system, my kids all wanted to invent their own planets.  So they ran back outside, grabbed more rocks, and returned to their planet-forming labs!

2.  Once the planets are dry, place them next to a big bowl of water and ask your children if they think any of them will float.  Ask why.  Invite them to test this hypothesis by dropping each planet in the bowl of water.  You can review the planets’ names with them as each planet is chosen and tested.  Explain that in real life Saturn is the least dense planet of all the planets in our solar system, even less dense than water!  Imagine how big a tub would have to be to hold Saturn!

Rocks in a bowl to show that they sink and float depending on the density of them.

3.  Invite your children to experiment with other objects around the yard and/or house.  Do sticks float?  What about all rocks?  Does the size of the rock make a difference?  What about leaves?

Leaves, rocks and balls in a bowl of water showing how different materials density affects them.
A child playing in the water

Once our kids saw that leaves floated, they wondered if brown leaves floated like green leaves.  Then, they had to check and see if crumpled and broken brown leaves floated too!

4.  Older children may enjoy a discussion on density and why things float.  An object will float in a liquid that is more dense than it is.  Saturn is the only planet less dense than water.  Here are the densities for the eight planets in our solar system.  The density of water is 1000 kg/cubic meter.

Mercury:  5427 kg/cubic meter

Venus:  5243 kg/cubic meter

Earth:  5514 kg/cubic meter

Mars:  3933 kg/cubic meter

Jupiter:  1326 kg/cubic meter

Saturn:  687 kg/cubic meter

Uranus:  1271 kg/cubic meter

Neptune:  1638 kg/cubic meter

Older children may also enjoy speculating about the Special Note below.

I hope you enjoyed this experiment and have a chance to check out No Place in Space!  If you and your children like science, you may enjoy this quick and easy science project, these fizzing dinosaur eggs, this frozen water magic science, this sparkly explosion, or this pumpkin science printable!  I would love to connect with you at Preschool Powol Packets or on social media!

A Special Note About Saturn Floating: While Saturn’s density is less than water, imagining a real bucket big enough for it to float in would be impossible.  Saturn’s outer layers are gas and would probably float right off the planet if it were dropped in a tub.  Also, like most floating objects, part of Saturn would be above the surface and part of it would be below the surface.  To actually be deep enough for Saturn to float, the bucket would have to be so, so deep that the pressure at the bottom would probably not allow the water to remain a normal liquid. Just a few thoughts for inquiring minds.  đź™‚

Carla Mae Jansen

Carla Mae Jansen is an educator, author, and mom who lives in Virginia, USA.

She loves going rock-hunting, eating chocolate, and exploring new places with her family.

She has a master’s degree in teaching science, and is always looking for something new to learn!

You can follow along with her publishing adventures atTurtle Trails Publishing.

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