FRED ANSWERS YOUR QUESTIONS

The image of the Moon shown on page 23 of AG 116 (Sep 2013) shows markings from asteroid collisions. Does Earth have the same density of hits or is the Moon like our ‘sacrificial anode’? Glen Miller, Millicent, SA

Most markings on the Moon do come from collisions with asteroids dating back to the Solar System’s origins. The large grey areas (basaltic plains) are impact basins, formed by large asteroids. Smaller objects produced the familiar craters. The Moon offers little protection to the Earth’s surface, which has been bombarded at a similar rate. However, tectonic activity on our planet has obliterated the most ancient terrestrial craters, leaving only relatively recent ones such as the Barringer Crater (age about 50,000 years), in Arizona. If you have a space question for Fred, email it to editorial@ausgeo.com.au