Author: Sarah Greenstreet and Sarah Eve Roberts
How old are the objects within our Solar System? One method scientists use to answer this important question is counting the number of craters on their surface. This information, combined with the time it takes for craters to form on each body, gives us a strong estimate how old the object is. In this activity students will put this method into practise to calculate the age of five bodies within our Solar System.
By studying a variety of objects and using several techniques, scientists have determined that the Solar System is 4.6 billion years old. It is believed that, give or take a few million years, this age is true for most of the objects in the Solar System.
In this activity students will use the crater counting method to calculate their own ages for several Solar System bodies. This exercise is precisely what scientists on the New Horizons mission (NASA’s first mission to Pluto and the Kuiper Belt beyond) are doing to determine the age of the dwarf planet Pluto and its moon, Charon.
Craters are formed when objects such as comets, asteroid and meteoroids crash into other objects; the energy of the impact creates a hole in the surface. All time estimates for crater formation used in this activity come from published calculations.
By the end of this activity students should be familiar with one method for calculating the age of objects within the Solar System, and using this method they should have determined rough estimates for the age of several cosmic bodies. Students should understand that scientists must deal with uncertainties in their research and how these can be minimised.
The activity is set up so that students across the group will determine a different crater count and cosmic age. Use this to introduce students to the uncertainty present in these types of calculations, and many other aspects of scientific research.
Once you have collect and compared results from each student, and calculated the average age of each body, open a discussion session on the following points:
Results in the activity will vary, below you will find only an example of results:
Charon: 16 craters = 4 billion years
Pluto: 17 craters = 4.25 billion years
Far side of the Moon: 23 craters = 4.6 billion years
Near side of the Moon: 15 craters = 1.2 billion years
Mercury: 37 craters = 0.4 billion years