Why do we always thing a Crater on Mars or even the Moon is ancient? Why couldn't it have happened last week?

Answer 1

A lot of people are looking at the moon right now.
If a significant object struck it, we would know.

Answer 2

Every once in a while, we find one that is relatively new. The dust, dirt, and rock that is exposed for new craters is very different than the old ones. That appearance ages over time.

Answer 3

NASA Captures Spectacular Image Of Mars’ Newest Crater

NASA’s Mars Reconnaissance Orbiter has snapped a stunning picture of the latest crater to form on Mars. The small indentation is located near the Southern Pole and it is believed to have happened sometime between July and September of 2018. The picture was taken on October 5.

Answer 4

We don't. Only you think so. Of course they can happen at any time but the fact is most of them ARE ancient.

Answer 5

Sometimes it is recent, but most craters were formed during the Late Heavy Bombardment, which occurred aeons ago. An example of a new crater is Giordano Bruno, which was formed on 18th June 1178.

Answer 6

new craters on mars would look different, as mars has an athmosphere and therefor winds.

Most craters on the moon have been described by people who lived centuries ago

Answer 7

Craters can happen at any time
Even on Earth, check out the Barringer Crater in the USA
circa 50, 000 Years ago
They can tell is from Carbon Aging the Tectites, and wear and tear
On Heavenly bodies the edges of the Craters can become Scalloped through gravity or even have newer Craters embedded in them
Earth too has had collisions with most of them being Eroded away
It took Echo Sounding from an Oil Company to find the Chixulub Crater
How long till we find echoes of Theia ?
Has anybody studied the Pacific Rim ?

Answer 8

A few "new" craters have been found; we judge how new they are by their surroundings, in most cases... An "older" crater may have more craters inside on on it's walls, indicating those are younger than the big crater itself. Recently, a new crater was believed to have been found on Mars - only a few weeks/months old - because they could compare photographs taken by orbiters months ago to what they look like today... But, in general - *most* craters on the moon have been there for a very, very long time; Mars has some weather - wind, at least - that may end up erasing craters eventually, so the oldest craters we see on Mars may be a little younger than those on the moon, as the moon has no atmosphere to erode the craters away.

Answer 9

"We" don't. Expert geologists have expert methods of estimating the ages of craters. Recent ones are easy to spot.

Answer 10

Because the crater matches images from a hundred years ago.