Jupiter’s moon Ganymede has an ancient impact structure called a furrow system. This system is the largest impact structure in the outer Solar System, and the impact should have significantly affected Ganymede’s early history.
Distribution of furrows and location of the center of the furrow system shown in the hemisphere that always faces away from Jupiter (top) and the cylindrical projection map of Ganymede (bottom). The gray regions represent geologically young terrain without furrows. Furrows (green lines) exist only on geologically old terrains (black regions). Image credit: Naoyuki Hirata, doi: 10.1038/s41598-024-69914-2.
Ganymede is the largest satellite in the Solar System and has many unique features, including tectonic troughs known as furrows.
Furrows are the oldest surface features recognized on Ganymede because they are crosscut by any impact craters with diameters exceeding 10 km. They can provide a window into the early history of this moon.
Furrows have been proposed to be fragments of multiring impact basin structures, similar to those of the Valhalla or Asgard basins on Callisto.
The largest furrow system is present across Galileo and Marius Regios — the so-called Galileo-Marius furrow system — and it is the remnant of an ancient giant impact, which extends concentrically from a single point of Ganymede.
“The Jupiter moons Io, Europa, Ganymede and Callisto all have interesting individual characteristics, but the one that caught my attention was these furrows on Ganymede,” said Kobe University planetologist Naoyuki Hirata, author of a paper published in the journal Scientific Reports.
“We know that this feature was created by an asteroid impact about 4 billion years ago, but we were unsure how big this impact was and what effect it had on the moon.”
First, Dr. Hirata realized that the purported location of the impact is almost precisely on the meridian farthest away from Jupiter.
“Drawing from similarities with an impact event on Pluto that caused the dwarf planet’s rotational axis to shift and that we learned about through NASA’s New Horizons spacecraft, this implied that Ganymede, too, had undergone such a reorientation,” he said.
According to the study, an asteroid that hit Ganymede probably had a diameter of around 300 km — about 20 times as large as the Chicxulub asteroid that hit Earth 65 million years ago and ended the age of the dinosaurs — and created a transient crater between 1,400 and 1,600 km in diameter.
Only an impact of this size would make it likely that the change in the distribution of mass could cause the moon’s rotational axis to shift into its current position. This result holds true irrespective of where on the surface the impact occurred.
“I want to understand the origin and evolution of Ganymede and other Jupiter moons,” Dr. Hirata said.
“The giant impact must have had a significant impact on the early evolution of Ganymede, but the thermal and structural effects of the impact on the interior of Ganymede have not yet been investigated at all.”
“I believe that further research applying the internal evolution of ice moons could be carried out next.”
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N. Hirata. 2024. Giant impact on early Ganymede and its subsequent reorientation. Sci Rep 14, 19982; doi: 10.1038/s41598-024-69914-2
Source : Breaking Science News