### IIA. HOW ARE CRATERS MADE?

Concepts:

• Scientific experimentation
• Observing and recording data
• Graphing
• Data analysis and interpretation
• Drawing conclusions
• Higher order thinking

Impact craters are made when an object or bolide impacts the surface of a planet or satellite. A bolide is any falling body such as a comet or meteorite. Many hands on impact simulation activities are available, and all involve dropping a series of bolides, with different masses, onto a simulated planetary surface. The planetary surface can be dry, for example made out of flour with a dusting of cocoa powder, or wet, such as a muddy composite of dirt or sand.

[A variety of cratering exercises are available. See Craters! ]

Components of Activity:

• Parameters to be varied should include:

• mass of impactor

• size of impactor (diameter)

• distance impactor falls (speed of impactor)

• composition of simulated planetary surface (wet, dry, hard, soft)

• Students should record data:

• input variables:

mass, size, height, surface composition

• results:

diameter of resulting crater, depth of crater, shape of crater, description of ejecta, other observations

• (optional) Graph results:

• mass of impactor vs. diameter of crater

• height impactor dropped from vs. diameter of crater

• etc.

Interpretation:

Q: What factors govern the size and shape of an impact crater?

A:

• mass of impactor

• size of impactor

• composition of impactor (ice, rock, iron)

• composition of target site (water / rock / sand)

• speed of impactor (height)

• atmosphere

Q: List the terrestrial planets, and which of the above factors contribute to the appearance of craters on each of the planets

A:The largest variation between planets is in size, composition, and atmosphere.

Planet size affects frequency and speed of impact. Larger planets have stronger gravitational fields, and attract more objects, which hit them at greater speeds.

Target composition affects the appearance of craters.

Atmosphere affects whether small craters exist.

• Earth: atmosphere, oceans + rock (no craters in water), large -> few craters

• Venus: atmosphere, rock, large -> no small craters

• Mars: thin atmosphere, rock, mid-sized -> no tiny craters

• Moon, Mercury: no atmosphere, rock, small -> lots of craters

Go to:

This module was written by Cynthia Phillips, Dept. of Planetary Sciences, University of Arizona, Tucson AZ, and funded in part by the NASA Spacegrant program.

Galileo Solid State Imaging Team Leader: Dr. Michael J. S. Belton

The SSI Education and Public Outreach webpages were originally created and managed by Matthew Fishburn and Elizabeth Alvarez with significant assistance from Kelly Bender, Ross Beyer, Detrick Branston, Stephanie Lyons, Eileen Ryan, and Nalin Samarasinha.

Last updated: September 17, 1999, by Matthew Fishburn