On Earth, there are a surprisingly scarce number of impact craters. Part of this lies in the fact that Earth’s surface is decorated by thousands of years of infrastructure, while Earth’s many bodies of water and plate tectonics take care of the rest (that’s not to say no such craters exist because they do and they are beautiful). However, with the exception of a small few, other planets and moons are typically a different story. Without some internal mechanism replenishing materials to cover craters up, these features remain on the surface indefinitely. Sometimes, we even have the technology to venture to these worlds and capture images that allow us to see scars left behind as a reminder of the havoc ancient pieces of space rock once wreaked.
On that note, the European Space Agency (ESA) has just released new images of Hellas Basin, an impact crater found on Mars that came into being about four billion years ago. The crater itself shows just how impressively destructive such a small object can be. It left behind a huge hole that spans more than 1,400 miles (2,253 kilometers) across and is 26,465 feet (7,152 meters) deep. (To put it in perspective, the crater is roughly half the size of Brazil — at least in surface area)
From this vantage point, we can see the unusual effects of something called “concentric crater fill,” places where concentric patterns are present in and near the crater, along with the small arcs that stretch away from the center. It is understood that the patterns are created as the result of Mars’ unsteady temperament early on in its history, when it was entangled in continuous cycle of freezing and thawing back out (back when Mars was much warmer and far more wet place).
To elaborate, the strange features likely formed over a long stretch of time. During Martian winters, snow would fall and cover the crater and its environment, yet before it had time to melt, Mars’ infamous dust would have already blanketed the snow, eventually becoming compacted into ice (if this mechanism is responsible, it stands to reason that ice might still lurk beneath the surface).
Hellas, which was captured by the high-resolution stereo camera on-board Mars Express, is merely a small part of a much larger whole; the Hellespontus Montes region (found in the southern hemisphere). Within it lies a number of mountains that form the rim of a huge basin. It’s so large, in fact, that under the right circumstances (and with a moderately powerful telescope), you can even see it for yourself.
In fact, the image below was taken from Melbourne, Australia earlier this year (on March 8th). The region Hellas dwells in (the “cap” near the top) is so distinct here because it was shrouded in the frost and clouds that manifest during Martian winters.
The much smaller region below is actually the northern polar cap, while Syrtis Major can be seen as the misshapen feature that stands against a sea of red.