Click for original.

Cool image time! The picture to the right is taken from a global mosaic created from images taken by the wide-view context camera on Mars Reconnaissance Orbiter (MRO). The original source image was probably a photograph taken on February 15, 2020.

I normally begin with an image from MRO’s high resolution camera, but the only images that camera took of this crater did not show it entirely. This context camera shows it in all its glory, what to my eye appears to be one of the weirdest craters I’ve seen on Mars.

First, note its oblong shape — 5.5 miles long and 3.7 miles wide — which appears to narrow to the southeast. It certainly appears that if this crater was caused by an impact, the bolide came in at a very low angle from the northwest, plowing this 700-foot-deep divot as it drove itself into the ground. Research has shown that an impact has to come in almost sideways to do this. Even at slightly higher angles the resulting craters will still appear round.

But wait, there’s more!

Click for original.

For the overview map showing the location of this crater, go to my cool image yesterday. It was just to the west of that featured image in the southern cratered highlands near the equator. I noticed it while preparing that image, and I immediately decided it was so weird I had to highlight it today.

The image to the right is a cropped and sharpened section taken of this crater by MRO’s high resolution camera on January 13, 2007. It focuses on the southwest end of the crater to get a closer look at the many concentric interior layers seen in the wide picture above. Though the layers strongly resemble glacier features found in many craters in the icy mid-latitudes, these layers are not glacial. This location is deep within Mars’ dry tropics, only about 300 miles north of the equator. There is no near surface ice here.

Instead, what I think we are looking at are the left-over remnants of either ice or liquid water that once filled this crater, but is now long gone. The layers represent the repeated cycles of filling and draining, with each filling depositing wet dust (mud) on the edges. Because the amount of water on Mars has been declining over time, each time the crater filled, it filled less, which is why the layers form this terraced pattern.

As I noted yesterday, researchers have found evidence in this particular region suggesting that springs of water once existed here in many craters. This adds weight to my hypothesis that these layers are evidence of a past lake.

In fact, this crater and this evidence of past liquid water made this crater one of the potential landing sites that scientists considered for the rover Curiosity. I know this because the science team labeled this 2007 high-resolution picture “Proposed MSL Site in Meridiani”, with “MSL” for Mars Science Laboratory (the official name for Curiosity) and Meridiani the name of this region.

In the end the scientists decided to send Curiosity to Gale Crater instead, on the other side of the planet. This region however very clearly still intrigues planetary scientists, considering the number of follow-up images I have posted. In fact, in 2020 they used MRO to take a second high resolution photo of this particular crater, to create a stereo image in order to better map its topography.

Mars is truly strange. It will be wonder to explore for the first colonists, for many generations. This particular place will likely be one of those wonders.