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In its 4.6 billion-year history, Mars has received its fair share of punches from falling asteroids and rushing comets.
Today the surface of the red planet is covered by no less than 43,000 impact craters larger than 5 kilometers; some ancient regions have received more blows than others.
In the ancient Martian highlands of Noachis Terra – a heavily hit region some 4 billion years ago – astronomers have identified a triple whammy crater made up of three overlapping basins.
This natural diagram of the Venn depressions is not as large as some other Noachis Terra craters, some of which may extend nearly 140 km (87 miles) in diameter, but the smallest crater in the lot is still a whopping 28 km wide.
And this is just one of the ancient footprints. With a small overlap, the largest adds another 45km in diameter.
The triple crater captured by the Mars Express High Resolution Stereo Camera (HRSC).
It is difficult to tell whether the triple impact crater is due to one or more collisions. The researchers say the impactor may have broken into three pieces before hitting the ground in close formation, but other examples of this destructive approach do not show such clear ridge definitions, nor do they overlap so sharply.
The double and triple impact craters are unusual to see but are not unheard of; we occasionally find them on Mars and even on Earth, although not all are formed equally.
In 2015, for example, astronomers noticed a similar triple crater in the Elysium Planitia near the equator of Mars (pictured below). At the time, the team speculated that it could be due to an asteroid breaking up in the atmosphere, or it could be due to a smaller asteroid orbiting a larger binary pair.
Triple impact crater in Elysium Planitia. (NASA / JPL-Caltech / University of Arizona)
In 2017, the Mars Reconnaissance Orbiter noticed an elongated depression from three joined impact craters, which astronomers believe probably came from three pieces flying in close formation.
Some have even speculated that the double craters are due to double asteroids, composed of two or more rocky bodies in close contact or in close orbit with each other. Only about 2% of all asteroids are thought to form from two or more bodies like this, but that doesn’t mean that sometimes they can’t collide with a planet and leave a scar.
“Another explanation could be a coincidence,” reads a press release on the latest triple impact crater, this time from the European Space Agency, “at different times, three separate impactors may have hit the surface of Mars in this one. position, creating a completely random overlap of craters “.
Considering how heavily this region of Mars was once bombed, experts say this is the most likely possibility, although it is certainly not the most interesting.
(ESA / DLR / FU Berlin / CC BY 3.0)
If, on the other hand, this is not due to three chance encounters and the impactor really broke before hitting Mars, this tells us something important about this planet: 4 billion years ago, the atmosphere of Mars was probably much harder to penetrate than it is now, and that implies heat and humidity.
Similar to other craters in the region, this triple impact crater displays flattened edges and shallow floors due to the wear and tear of time. Some of its signs even suggest a glacier-like flow, which may have helped soften the ground below, gradually filling the indentation as the ice melted.
As scars often do, this speaks volumes about the past.
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