How we discovered two unusually large craters, and the secrets they reveal

Mars: How we discovered two unusually large craters--and the secrets they reveal

Dusty solar panel from InSight. Credit: NASA/JPL

Most of the worlds of our solar system are riddled with impact craters. These testify to the violence of the early days of the Sun, when asteroids, comets, and entire planets routinely collided and annihilated one another.

Our moon most likely formed as a result of one of these collisions, and is itself home to the largest collision feature in the solar system – Antarctica/Aitken Basin, about 2500 km across. Mars’ vast, flat northern deserts may also have formed during a massive collision about 4 billion years ago.

Today’s solar system is a much quieter place. But impacts from meteorites remain one of the dominant processes shaping planetary landscapes on most worlds other than Earth. Now our new larger recent study impact etching on Mars Posted in Sciencessheds new light on the interior of the Red Planet.

Examining impact craters can teach us a lot—from understanding the composition and size of the asteroids or comets that created them, to discovering the properties of planetary surfaces and interiors. In fact, the drill’s interior can be used to study otherwise inaccessible subterranean geology. The degree of craters on a surface can also be used to estimate its age: the older it is, the more craters (usually).

Late last year, NASA’s InSight rover, which has been on Mars “listening” for seismic waves in the planet’s interior, detected two massive “earthquakes” about 90 days apart—among the largest we’ve seen so far during our research.

These earthquakes were somewhat different from previous earthquakes recorded by InSight. For example, they appear to be what we call “surface waves” – that is, seismic waves that propagate in the outer layers of the Martian crust ( superficial layer).

These types of waves are rare. It is also particularly exciting because it allows us to “map” the structure of the very unusual Martian crust, which is much flatter in Northern Hemisphere and thicker and more mountainous in the south.

Mars: How we discovered two unusually large craters--and the secrets they reveal

Mars Insight landing site. Credit: Doyeon Kim, Martin van Driel, Christian Boom

Mars detective work

We can say that the swamps probably had a shallower origin—likely from a massive impact event rather than from processes deeper within the planet’s interior. By analyzing the seismic waves recorded by InSight, we were also able to determine the approximate epicenter, or point of origin, for earthquakes. Because these two earthquakes were so unusual, we asked for follow-up observations from Mars Reconnaissance Orbiter spacecraft orbiting the planet.

The results were absolutely amazing. The epicenters of both outcrops have been found to correlate with the sites of massive black smudges on the planet’s surface—the blast zones of the new impact craters. Looking back at the old, low-resolution images allowed the imaging team to pinpoint the exact dates for the formation of the craters, which coincided exactly with the time the swamps were discovered by InSight.

The craters themselves were enormous – about 130 meters and 150 meters in diameter, respectively. The “blast zones”, created by shock waves from meteorites entering the atmosphere and impacting the surface, extended for tens of kilometres. These were by far the largest new craters we’ve seen forming anywhere in the solar system.

The larger of the two craters was only about thirty degrees north of the Martian equator—by Mars standards, subtropical latitude. at the bottom of crater They were chunks of what was determined to be ice (of water), excavated by the impacting body as it penetrated into an underground frozen layer. This was the closest to the equator that we’ve seen ice, and it means there’s likely to be more water on Mars (albeit frozen) than previously thought. This is especially important if humans are going to settle there someday.

As it turned out, the surface waves from one of the events were so powerful that they were actually recorded by InSight after traveling in both directions around the planet – a first in seismology.

through analysis surface waves, we were also able to form an image of the crustal structure. Preliminary results indicate that the differences between nordic and Southern Hemisphere It may be more superficial than previously thought. Specifically, some of the crustal variations appeared to be confined to the region very close to the surface rather than extending much deeper. The reason for the great difference between the northern and southern hemispheres, although they are very similar at shallow depths, is still a bit of a mystery.

We also don’t know why these two craters formed so close to each other in time – they were likely much closer than random statistics would indicate. One of the theories we explored was if the asteroid crashed into orbit around Mars and the fragments slowly re-entered the atmosphere over several months, creating various craters. But the lack of any other craters of similar size or direct evidence for this makes it difficult to prove.

Unfortunately, the discovery of these impact events is likely to be one of the last results of the InSight mission. The spacecraft’s solar panels are now so dusty that it’s impossible to keep the batteries charged enough to keep them running. Although we’ll keep listening as long as we can, after sending the next set of seismometers to Mars we can explore some of these unanswered questions about impact events on the Red Planet.

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