The Moon Project - Craters

Lunar Craters

Craters on the Moon are caused by asteroids and meteorites colliding with the lunar surface. The Moon's surface is covered with thousands of craters. Why does the Moon have so many craters compared to the Earth? Unlike the Earth, the Moon has no atmosphere to protect itself from impacting bodies. It also has very little geologic activity (like volcanoes) or weathering (from wind or rain) so craters remain intact from billions of years. The Earth is also covered in water and vegetation which easily disguises impact craters.

Types of craters

	The largest craters on the Moon, like Mare Imbrium which is over 1100 km in diameter, have been flooded by lava and we can only see parts of their circular outline. Because these dark "mare" (which means 'sea') have few craters on them, they must be younger that the surrounding areas.
	Simple craters like Moltke (which is 6.5 km in diameter and 1.3 km deep), have a smooth bowl-like shape with smooth walls. Most small craters less than about 15 km in diameter are simple craters.
	Complex craters like Tycho (which is 85 km in diameter and 4.5 km deep), have well defined crater rims and a central peak. Most craters between 20 and 175 km in diameter and complex craters.
	Larger impact basins, like the 310 km diameter Schrödinger crater and 330 km diameter Mare Orientale, generally have ring-shaped uplifted regions in the centre of the crater. Impact basins are usually at least 300 km in diameter.

Here is an animation of a crater forming (from a laboratory experiment).

And here is how you can make craters in the class room! See the animation and read the notes.

For a details map of the Moon's surface with craters, see Google Moon.

Some definitions
• meteoroid
• meteorite
• meteor (a.k.a. "shooting star")
• meteor shower

Scientists in Schools program - run with Hartwell Primary School, Footscray Primary School and St Joseph's Primary School.
Leaders: Dr Sarah Maddison (Swinburne University)

Last Updated: July 2010

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