Caroline Herschel was a famous astronomer. She discovered eight comets, and made observations of nearby stars and distant galaxies. She did all this 200 years ago, during a time when women didn’t usually have jobs in science, and she was the first woman to be paid for her scientific work.

You will need...

A metal or plastic tray or plate (it is best not to use a breakable one)
Some flour
Some cocoa powder
A few pebbles or marbles - steel ball bearing are good if you have a magnet that will pick them up.  You can even try with larger balls.

How long will it take?

It will take up to half an hour to put together the experiment and try out a number of different projectiles.  Students may want to take longer looking up images of real craters.

What to do...

Once the students have carried out the experiment they may want to take some photos of their craters so they can compare them to real craters.  The flour / cocoa powder tends to be unstable and the craters will collapse if the tray is knocked.  In fact, this is a good example of the weathering of craters on Earth!

Students should be able to find pictures of craters on Earth, the Moon, Mercury and Mars, as well as on some of the moons of the gas giant planets.  Venus does have some craters, but the thick atmosphere stops smaller collisions.

Craters are harder to see on Earth than the Moon because the craters have been weathered.

Students may want to look up the image of Mimas, one of Saturn's moons which has a huge crater.

Curriculum Links


Working scientifically

Experimental skills and investigations

  • ask questions and develop a line of enquiry based on observations of the real world, alongside prior knowledge and experience

Analysis and evaluation

  • interpret observations and data, including identifying patterns and using observations, measurements and data to draw conclusions.


Scottish Curriculum Links


Planet Earth - Space

SCN 3-06a

By using my knowledge of our solar system and the basic needs of living things, I can produce a reasoned argument on the likelihood of life existing elsewhere in the universe.


SCN 4-06a By researching developments used to observe or explore space, I can illustrate how our knowledge of the universe has evolved over time.



CometComets were spotted in the sky thousands of years ago. At that time, people often thought their sudden appearance was a sign that something disastrous was about to happen. Indeed, these stories may have been based on fact, as the Earth was bombarded by comets millions of years ago, and it continues to be at risk of collision with a comet today!

Most of the time comets are found far out in the solar system. But some comets have orbits which take them closer to the sun, and when they do the ice and frozen carbon dioxide boils off their surface, taking chunks of rock with it, and creating the comet's tail.

Key fact: Comets are made from rock, ice and frozen carbon dioxide and they orbit around the sun.

Why are comets important?

Although a comet colliding with the Earth would have been disastrous at the time - many believe the dinosaurs were wiped out by a comet - comets weren't entirely bad news. In fact, it is unlikely that life would exist without them.

It was the water in the form of ice in the comets which was so important to life. Billions of years ago, the number of comets hitting earth would have supplied all the oceans on the planet with water, and life depends on this water.

Today, comet strikes are very rare, but a comet colliding with Earth would certainly be catastrophic. The careful observations made by astronomers like Caroline Herschel continue today. Now, we can send special instruments into space, to study what comets are made of, and to map their orbits, so we can predict where they will go and know if we are at risk.

Key fact: Caroline Herschel's research into comets still helps us today, to predict whether the Earth may be at risk from collision with a comet.




The moon 'Mimas'Cocoa craters

What do comet collisions do to the surface of a planet?

Download the pdf worksheet here.

You will need...

A metal or plastic tray or plate (it is best not to use a breakable one)
Some flour
Some cocoa powder
A few pebbles or marbles. (Steel ball bearings are good if you have a magnet that will pick them up, or you can even try with larger balls.)

What to do...

1.  Take your plastic tray and cover it in flour. You will need a depth of one or two centimetres. Don't make it too deep: if you have very small pebbles they will tend to get buried in the soft flour.

2.  Cover the flour with a thin layer of cocoa powder, making sure you cover the entire surface. Use a sieve to help keep out any lumps.

3.  Drop a pebble onto the flour, from a height of about 10cm to 30 cm above the tray.

4.  Carefully pick out the pebble, trying as hard as possible not to disturb the flour.  (If you use steel ball bearings, the magnet works brilliantly for this.) When you have removed the pebble, examine the crater that has been formed.

5.  Try again by dropping the pebble from a different height, or throwing it (gently) at an angle, and see if a different sort of crater has formed. Different sized and shaped pebbles will also make different craters.

6.  Now look up some pictures of craters, online or in astronomy books, particularly ones on the moon, and see whether they match the craters you have made. Also look at craters on Mercury, Venus and Mars. Some of the gas giant planets also have rocky moons, such as Jupiter or Saturn.


Can you answer the following questions?

  • What planets have impact craters on them?
  • Why, if the Earth was bombarded with comets, are there not as many craters on Earth as there are on the moon?