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Astronomers may have identified the largest impact structure in our solar system



Jupiter Ganymede Moon is a very special piece of rock.

It is the largest and most massive moon in the Solar System. It is the only moon in the Solar System that generates its own magnetic field. It has the most liquid water of any organ of the Solar System. And now, scientists have discovered, it may have the largest impact structure ever identified.

Astronomers have discovered that tectonic valleys known as furrows, thought to be the oldest geological features in Ganymede, form a series of concentric rings up to 7,800 kilometers (4,847 miles) beyond, as if something were crashing on the Moon.

This does not yet need to be confirmed by more observations, but if the rings were indeed formed by an impact, it would greatly outperform all other confirmed impact structures in the solar system.

Ganymede furrows are tufts of sharp, raised edges and have long been considered to be the result of major influences early in Ganymede history, when its lithosphere was relatively thin and weak. But a Ganymede data analysis led by planetologist Naoyuki Hirata of Kobe University̵

7;s Graduate School of Science tells a slightly different story.

To try to better understand the story of Ganymede, Hirata and his colleagues took a closer look at images taken by spacecraft – both the Voyager probes, which flew from Jupiter in 1979, and the orbiter Galileo Jupiter, which studied the planet and its satellites from 1995 to 2003.

These images show that Ganymede has a complex geological history. The moon is divided into two types of terrain – Dark Terrain and Bright Terrain. The Bright Terrain is lighter in color and relatively absent in the crater – suggesting it is much younger than the heavier Dark Terrain.

gany furr(NASA / Hirata et al.)

This older terrain is pocket and rugged. And those craters were made over previous scratches – grooves that can be found on most of Dark Terrain.

The team carefully catalyzed all the furrows, drawing them across the surface of Ganymede. They found that almost all of these structures, instead of being erroneously arranged around multiple points of impact, were concentrated at a single point.

Moreover, the valleys are wrapped around the Moon, stretching up to 7,800 kilometers. Ganymede is 5,268 kilometers (3,273 miles) in diameter – so it’s a pretty big ruin, to put it mildly.

impact gif(Hirata et al., Icarus 2020)

The next step in the research was to determine what might have caused such a structure. The team executed simulations of various scenarios and found that the most likely culprit was an asteroid 150 kilometers (93 miles) beyond, crashing into the Moon at a speed of about 20 kilometers per second (12 miles per second).

This would have happened during the late bombing, about 4 billion years ago, when Ganymede was quite young. During this period, the Moon is thought to have received an absolute commercial pumice due to the gravitational concentration of Jupiter – so a giant impact is certainly possible.

In addition, a similar structure can be found nearby. At Callisto on Jupiter Moon, Valhalla Crater is a multi-ring impact crater up to 3,800 kilometers (2,360 miles) in diameter, thought to be between 2 and 4 billion years old.

Valhalla Crater is also the current record holder for the largest impact structure in the solar system, followed by Utopia Planitia on Mars, an impact pond (not a multi-ring structure) 3,300 kilometers (2,050 miles) beyond.

The new discovery awaits confirmation, but perhaps we should not wait long to discover it. If the furrows are caused by a giant impact, there must be a gravitational anomaly at the site of impact, as seen in other large impact structures such as the South-Aitken Pole Basin on the Moon.

Now that we know how to look for it, maybe the Jupiter Juno probe could be used to look for this anomaly. Moreover, the Space Agency’s Jupiter Icy Moon Explorer (AUU) probe will launch in 2022, the first mission dedicated to studying Jupiter moons. She, even more than Juno, can shed light on the cause of these mysterious structures.

The research is published in Icarus.


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