Here's Something Rare: a Martian Crater That isn't a Circle. What Happened?

By Nancy Atkinson April 22, 2022
Here's Something Rare: a Martian Crater That isn't a Circle. What Happened?

Most impact craters are usually circular and fairly symmetric, but not all. This odd-shaped crater on Mars is obviously an impact crater, but it has a unique oblong shape. What happened?

Most craters are circular shape due to material ejecting out in all directions as a result of an impact. Below is a group of impact craters in Noachis Terra, a large region in Mars’ southern hemisphere. These are all classified as simple craters, which are small bowl-shaped, smooth-walled craters.

Round simple crater in Noachis Terra. Credit: NASA/JPL-Caltech/UArizona. You can see more detail of this region here. https://www.uahirise.org/ESP_016104_1460

Complex craters, on the other hand, are large craters with complicated features, such as terraces, central peaks, and rims and walls their own features. Oblong craters, like one in the lead image – which is also located in Noachis Terra -- can sometimes be created by impacts striking the surface at a very low, grazing angle.

But scientists from the HiRISE (High Resolution Imaging Science Experiment) camera on the Mars Reconnaissance Orbiter don’t think that would explain this crater’s shape. It is definitely a complex crater, and it has some tell-tale features that might explain the unique shape.

An odd shaped crater in Noachis Terra on Mars. Credit: NASA/JPL-Caltech/UArizona

The HiRISE team points out that large blocks of material in the northeast and northwest corners look like they have slid into the crater. These collapses have extended the crater in those directions giving it an oblong appearance.

For comparison, here’s an oblong impact crater where the shape is due to a small body striking the surface at a very shallow angle. This platypus-tail-shaped depression is called Orcus Patera, which is obviously an older feature, since newer impact craters dot its surface.

Orcus Patera is an enigmatic elliptical depression. Credits: ESA/DLR/FU Berlin (G. Neukum

You can see all shapes and kinds of craters in incredible detail at the HiRISE website. HiRISE is the most powerful camera ever sent to another planet, and is one of six instruments onboard the Mars Reconnaissance Orbiter. It has taken hundreds of thousands of high-resolution images of Mars surface since it arrived in orbit of the Red Planet in 2006.

Nancy Atkinson

Nancy Atkinson

Nancy Atkinson is a space journalist and author with a passion for telling the stories of people involved in space exploration and astronomy. She is currently retired from daily writing, but worked at Universe Today for 20 years as a writer and editor. She also contributed articles to The Planetary Society, Ad Astra (National Space Society), New Scientist and many other online outlets.

Her 2019 book, "Eight Years to the Moon: The History of the Apollo Missions,” shares the untold stories of engineers and scientists who worked behind the scenes to make the Apollo program so successful, despite the daunting odds against it. Her first book “Incredible Stories From Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos” (2016) tells the stories of 37 scientists and engineers that work on several current NASA robotic missions to explore the solar system and beyond.

Nancy is also a NASA/JPL Solar System Ambassador, and through this program, she has the opportunity to share her passion of space and astronomy with children and adults through presentations and programs. Nancy's personal website is nancyatkinson.com