Crater counting
Encyclopedia
Crater counting is a method for estimating the age of a planet's surface. The method is based upon the assumptions that a new surface forms with zero impact crater
s, and that impact craters accumulate at some constant rate. The method has been calibrated using the ages of samples returned from the Moon
.
has been questioned due to formation of large amounts of secondary crater
s. In one case, the impact that created Zunil crater
produced about a hundred secondary craters, some more than 1000 km from the primary impact. If similar impacts also produced comparable amounts of secondaries, it would mean a particular crater-free area of Mars had not been "splattered by a large, infrequent primary crater", as opposed to suffering relatively few small primary impacts since its formation.
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
s, and that impact craters accumulate at some constant rate. The method has been calibrated using the ages of samples returned from the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
.
Crater counting on Mars
The accuracy of age estimates of geologically young surfaces based on crater counting on MarsMars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
has been questioned due to formation of large amounts of secondary crater
Secondary crater
Secondary craters are impact craters formed by the ejecta that was thrown out of a larger crater. They sometimes form radial crater chains.-External links:*...
s. In one case, the impact that created Zunil crater
Zunil (crater)
Zunil is an impact crater near the Cerberus Fossae on Mars, with a diameter of . It is named after a town in Guatemala. Visible in images from the Viking 1 and Viking 2 Mars orbiters in the 1970s, Zunil was subsequently imaged at higher resolution for the first time by the Mars Global Surveyor ...
produced about a hundred secondary craters, some more than 1000 km from the primary impact. If similar impacts also produced comparable amounts of secondaries, it would mean a particular crater-free area of Mars had not been "splattered by a large, infrequent primary crater", as opposed to suffering relatively few small primary impacts since its formation.