The five most impressive geological structures in the solar system

When we talk about amazing geological features, we often limit ourselves to those of the Earth. But as a geologist, I think it’s crazy – there are so many structures on other worlds that can excite and inspire, and that can put processes on our own planet into perspective.

Here are, in no particular order, the five geological structures of the solar system (outside Earth) that impress me the most.

The biggest canyon

I left out the largest volcano in the solar system, Olympus Mons on Mars, to include the most spectacular canyon on this planet, Valles Marineris. At 3,000 km long, hundreds of kilometers wide and up to eight kilometers deep, this is the best result in space. If you were lucky enough to stand on one edge, the opposite edge would be way beyond the horizon.

It was probably initiated by fracking when an adjacent volcanic region (called Tharsis) began to swell upward, but was widened and deepened by a series of catastrophic flooding that peaked over 3 billion years ago. ‘years.

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The folded mountains of Venus

We will learn a lot more about Venus in the 2030s when two missions from NASA and one from ESA (European Space Agency) arrive. Venus is almost the same size, mass, and density as Earth, leading geologists to wonder why it lacks Earth-style plate tectonics and why (or even if) it has relatively little active volcanism. . How does the planet evacuate its heat?

I find it reassuring that at least some aspects of the geology of Venus seem familiar. For example, the northern margin of the highlands named Ovda Regio looks surprisingly similar, apart from the absence of rivers flowing through the eroded fold-like pattern, to “bend mountains” on Earth such as the Appalachians, which are the result. of a collision between the continents.

Thundered Mercury

I’m cheating a bit with my next example, as it’s both one of the solar system’s largest impact basins and an explosive volcano within. Mercury’s 1,550 km-diameter Caloris Basin was formed by a major asteroid impact about 3.5 billion years ago, and soon after, its ground was flooded with lava.

Sometime later, a series of explosive eruptions carved holes several miles deep through solidified lava near the edge of the basin where the lava cap was thinnest. These volcanic ash particles were projected over a distance of several tens of kilometers. One of these deposits, named Agwo Facula, surrounds the explosive vent that I have chosen as an example.

The explosive eruptions are caused by the force of the expanding gas and are a surprising discovery about Mercury, which was previously expected to be deprived of these volatile substances by the proximity of the Sun – the heat would have made them boil. Scientists suspect that there were in fact several explosive eruptions, possibly spaced over an extended period of time. This means that volatile gas-generating materials (whose composition will remain uncertain until the start of work on Esa’s BepiColombo mission in 2026) were repeatedly available in the magmas of Mercury.

The highest cliff?

In land areas rich in soil or vegetation, cliffs offer the greatest exposures of clean rock. While dangerous to approach, they reveal an unbroken cross section of rock and can be great for fossil hunting. Because geologists love them so much, I give you the Rupes de Verona, seven kilometers high. This is a feature of Uranus’ small moon, Miranda, which is often described as “the highest cliff in the solar system,” including on a recent NASA website. It even goes so far as to notice that if you were careless enough to drop from the top, it would take you 12 minutes to drop to the bottom.

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This is absurd, because Verona Rupes is far from vertical. The only images we have of it come from Voyager 2, captured during its flyby of Uranus in 1986. It is undeniably impressive, almost certainly being a geological fault where a block of Miranda’s icy crust (the most “shell”). outer planet) has moved down against the adjacent block.

However, the obliquity of view is deceptive, making it impossible to be sure of the tilt of the face – it is likely tilted less than 45 degrees. If you stumbled at the top, I doubt you would even slip down. The face appears to be very smooth in the best low-res image we have, but at Miranda’s -170 ° C daytime temperature, the water ice has high friction and is not slippery at all.

Titan’s Drowned Coast

For my final example, luckily I could have chosen virtually anywhere on Pluto, but instead, I opted for an Earth-like haunting coastline on Saturn’s largest moon, Titan. Here, a large depression in Titan’s water ice “bedrock” harbors a sea of ​​liquid methane named Ligeia Mare.

The valleys carved out by rivers of methane flowing into the sea were obviously inundated as the sea level rose. This coastline with intricate indentations strongly reminds me of Oman’s Musandam Peninsula, on the southern side of the Strait of Hormuz. There, the local crust has been deformed downward due to the ongoing collision between Arabia and the Asian continents. Did something similar happen on Titan? We don’t know yet, but the way coastal geomorphology changes around Ligeia Mare suggests to me that its flooded valleys are more than just a result of rising liquid levels.

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Rock and liquid water on Earth, icy water ice and liquid methane on Titan – it makes little difference. Their mutual interactions are the same, and so we see geology repeating itself on different worlds.