Mercury may be hot, but it appears to be cooling. That’s the conclusion of a new study that looked for the types of features on Mercury that could form when the planets’ surfaces shrink due to cooling. These vertical rifts, called “grabens,” are not only common across the planet’s surface, but they appear to have formed within the past few hundred million years — and perhaps more recently.
All of this suggests that pressures from a cold planet still exist on the smallest non-dwarf planet in the solar system.
The planet building process necessarily generates a lot of heat, as impactors of different sizes deliver matter and energy to the growing planet. The radioactive elements they transport can also heat the planet’s interior. For the rocky planets in our solar system, this heat means contrasting interiors, with layers of light rock above the liquid core.
However, over time, this heat escapes into space, allowing the interiors of the planets to gradually cool. Since smaller planets contain less hot material relative to their surface area, this cooling occurs more quickly on Mars and Mercury.
Cooling could have major impacts on the planet. Once things cool enough, that means the end of liquid nuclei and the loss of any magnetic fields generated during their rotation. When the rocks above the core cool, they also solidify, stopping processes like volcanism and plate tectonics that we see on Earth.
But this does not mean the end of all tectonic activity, because the cooling itself can generate other pressures that can reshape the planetary surface. Most materials contract when they cool, becoming denser. Since planets cool from the outside in, the crusts are already compact and compact when the interior cools. As the planet’s interior cools, its pressure will gradually pull the pillar out from under the crust.
This creates an enormous amount of stress on the hard shell, which responds the only way it can: by breaking. Some crustal masses will follow the downward contracting core. This pushes the adjacent shell blocks upward, since there is not enough room for all the material to fall. The result is A Grabennamed after the German word for ditch.
Lots of grabbing
Grabens were first identified on Earth, where the interior remains warm, and they usually form where the Earth’s crust has stretched to the point of breaking. But they have since been identified in many other objects in the solar system. The new work, carried out by a small European team, conducted a comprehensive search for images of Mercury taken by the MESSENGER spacecraft, which completed its mission to the planet eight years ago.
Using the extensive image archive created by MESSENGER, the researchers selected terrains that showed signs of pressure from pressures generated by Mercury’s pressure, and then examined these terrains with the naked eye. Within these areas, the researchers identified 727 possible individuals, with about 200 of them being highly confident. Once identified, the researchers used shadows to try to estimate the depth of the shot in cases where the shooting angle allowed it.
The mere fact that these trenches are not filled by active processes on Mercury’s surface (primarily impacts, formation and dispersal of regolith) suggests that the trenches are rather small. Their widespread nature indicates that tectonic activity is widespread on the planet. The majority of the carapaces we see here are located inside a large impact crater called an impact crater Calorie poolThinner veneers may be more susceptible to cracking.
In general, most of the pods were less than 50 m deep. But a fair number were between 50 and 100 meters deep, and at least 20 of them were more than 100 meters deep. If these structures were ancient, they simply would not be that deep. Based on the relationship between hook length and depth as seen on Earth and the Moon, the authors estimate that most hooks are less than 200 million years old and possibly younger.
This means that the cooling of Mercury is likely an ongoing process, one that still leads to tectonic activity. While we’re unlikely to get a lander there anytime soon to confirm this, we will get a new view of Mercury starting in 2025, when the European Space Agency launches the lander mission. Baby Colombo The spacecraft goes into orbit.
Natural Earth Sciences, 2023. DOI: 10.1038/s41561-023-01281-5 (About digital IDs).
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