The moon of Jupiter Ganymede is a rather special rock of rock.
It is the largest and most massive moon in the solar system. It is the only moon of the Solar System that generates its own magnetic field. It has the most liquid water of any body of the Solar System. And now, scientists have discovered, it may have the largest impact structure ever identified.
Astronomers have found that the tectonic troughs, known as furrows, are thought to be the oldest geological features on Ganymede, forming a series of concentric rings up to 7,800 kilometers (4,847 miles), just as if it had hit something in the moon.
This has yet to be confirmed with more observations, but if the rings were in fact formed by an impact, it would largely overlook all other confirmed impact structures in the solar system.
Ganymede’s furrows are troughed with sharp, raised edges, and have long been considered to be the result of great influence early in Ganymede’s history, when its lithosphere was relatively thin and weak. But a reanalysis of Ganymede data led by planetologist Naoyuki Hirata of the Kobe University Graduate School of Science tells a slightly different story.
In an attempt to better understand Ganymede’s history, Hirata and his colleagues visited images obtained by spacecraft – both Voyager probes, which flew through Jupiter in 1979, and the Galileo Jupiter orbiter, which orbits the planet and its satellites. studied from 1995 to 2003.
These images show that Ganymede has a complex geological history. The moon is divided into two types of terrain – the Dark Terrain and the Bright Terrain. The Light Terrain is lighter in color, and relatively lacking in craters – suggesting that it is much younger than the very crisp Dark Terrain.
(NASA / Hirata et al.)
This older terrain is pocked and cratered. And those craters were made on top of earlier scars – the furrows that can be found in most of the Dark Terrain.
The team carefully cataloged all the furrows, and mapped them across the surface of Ganymede. They found that almost all of these structures, rather than being randomly arranged around many impact points, were concentrically oriented at one point.
Furthermore, the bins wrestle around the moon, which spans up to 7,800 kilometers. The diameter of Ganymede is 5,268 kilometers (3,273 miles) – so that’s a pretty huge wrinkle, to say the least.
(Hirata et al., Icarus, 2020)
The next step in the investigation was to determine what could have caused such a structure. The team ran simulations of various scenarios, and found that the most likely culprit in an asteroid was 150 kilometers (93 miles) across, hitting the moon at a speed of about 20 kilometers per second (12 miles per second).
This would have taken place during the Late Heavy Bombardment, about 4 billion years ago, when Ganymede was quite young. During this period, the moon is thought to have taken an absolute cometic pummeling due to gravitational focus by Jupiter – so a gigantic impact is certainly plausible.
In addition, a similar structure can be found nearby. On Jupiter’s moon Callisto, the Valhalla crater is a multifunctional ring crater with a maximum diameter of 3,800 kilometers (2,360 miles), thought to be between 2 and 4 billion years old.
The Valhalla crater is also the current record holder for the largest impact structure in the solar system, followed by the Utopia Planitia on Mars, an impact basin (not a multi-ring structure) over 3,300 kilometers (2,050 miles).
The new discovery is awaiting confirmation, but we may not have to wait long to find out. If the furrows were caused by a giant impact, there would have to be a gravity anomaly at the impact site, as seen in other large impact structures, such as the South Pole-Aitken Basin on the moon.
Now that we know what to look for, perhaps Jupiter’s probe Juno could be used to search for this anomaly. In addition, the Jupiter Icy Moon Explorer (JUICE) probe of the European Space Agency will launch in 2022, the first dedicated mission to study the moons of Jupiter. It, even more than Juno, could shed light on the cause of these mysterious structures.
The study was published in Icarus.
.
