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ESA’s Mars Express spacecraft acquired this image of a triple crater on Mars on August 6, 2020. The largest is about 45 km in diameter and the smallest is about 28 km. Image via ESA.
The European Space Agency (ESA) released the above image late last month (October 29, 2020), showing a triple crater in a particularly old part of the southern hemisphere of Mars. This region of Mars – known as Noachis Terra – was heavily bombed early in our solar system’s history, around 4 billion years ago, when debris left behind by the birth of the planets broke away . Do you see the rounded edges of these craters? It is a sign that they are old and worn out over time. How would such a crater triplet form? There are different possibilities.
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One possible explanation, ESA said – and considered the most likely explanation – is that the incoming debris (what we might now call an asteroid or comet) shattered into three pieces before hitting the ground, forming the trio of craters on impact. But, ESA added:
Not all “ multiple impactors ” leave such clean and neat features in their wake, with many instead showing elongated, non-circular, side-by-side or only partially overlapping recesses.
Another explanation could be a coincidence: At different points in time, three separate impactors could have struck the surface of Mars at that location, creating a sharp overlay of craters completely by chance.
It is interesting to note that if the impactor did indeed fragment and rupture, it may imply that the atmosphere of [Mars in its Noachian era, 3.7 to 4.1 billion years ago] was much denser – and more difficult to penetrate – than today.
This points to an ancient Mars that was much hotter and wetter than the cold, arid world we see today. Observations from many missions support this view and return evidence that water once flowed over the Red Planet in great quantities, revealing features such as ancient river valley systems and large lake basins that are believed to have formed during the Noachian period.
Like many of the ancient and eroded craters of the southern highlands of Mars, these three craters have flattened edges, shallow floors, and have filled with sediment in the 4 billion years since their formation. There is also evidence of ice here – the smaller crater has markings that are usually created when ice and debris crawls over a surface, much like mixed rock and ice glaciers or ice glaciers. covered with debris move through alpine regions of the Earth.
ESA also said that – in the image above – you can see signs of other craters, as indicated by the round sunken surface plates on the top right and bottom left. In fact, ESA said:
… Despite the cratered nature of Noachis Terra, the environment around this treble is surprisingly smooth for such ancient terrain. Only a handful of the surrounding small craters appear to have clear, sharply defined edges and bowls, indicating that they are relatively young and have yet to begin to seriously erode. Overall, it appears that the older craters in this area have “melted” to the surface – a phenomenon which, again, is due to ice.
As the ice just below the surface of Mars sinks and melts over millions of years, the ground becomes softer. This soft, ice-rich soil sags faster and fills in indentations and depressions more easily, contributing to the smoothness of this part of Noachis Terra. This suggests that there must be a large amount of water present on Mars, at least during the Noachian period, capable of producing an abundant glacier-like flow of ice.
Understanding the history of Mars and mapping in detail the features covering the planet’s surface is a key objective of Mars Express.
Triple crater in context in the ancient Martian highlands, in particular in the region of Noachis Terra. The area enclosed by the bold white box indicates the area imaged by the Mars Express High Resolution Stereo Camera (HRSC) on August 6, 2020, during orbit 20982. Image via ESA.
Bottom line: Late last month, the European Space Agency released an interesting image from Mars Express, showing an aged triple crater. Scientists are studying this image to learn more about the history of Mars.
Via ESA
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