The five most impressive geological structures in the solar system

When we talk about amazing geological features, we often limit ourselves to those on 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 (above Earth) that impress me the most.

The largest 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. Measuring 3,000 km long, hundreds of kilometers wide and up to eight kilometers deep, it is best viewed from space. If you were lucky enough to stand on one edge, the opposite edge would be well beyond the horizon.

Valles Marineris seen in a color-coded topographical view as though it were 5,000 km above the surface (left) and imaged by the high-resolution stereo camera on Esa’s Mars Express (right). Google Earth and NASA/USGS/ESA/DLR/FU Berlin (G. Neukum)

It was probably initiated by fracturing when an adjacent volcanic region (called Tharsis) began to bulge upwards, but was widened and deepened by a series of catastrophic floods that peaked over 3 billion years ago. of years.

Folded Mountains of Venus

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

Image of the wrinkled mountains on Venus.
Bend mountains at Ovda Regio, Venus. The insert is a similar view of part of Applachia in central Pennsylvania. NASA/JPL

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

Lightning Mercury

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

Some time later, a series of explosive eruptions carved holes several kilometers deep through the solidified lava near the edge of the basin where the lava cap was thinnest. These sprayed particles of volcanic ash over a range of tens of kilometers. One such deposit, named Agwo Facula, surrounds the explosive vent I have chosen as an example.

Images of the Caloris basin of Mercury.
Right: Most of Mercury’s Caloris Basin, its floor covered in dull, orange lava. Brighter orange spots are remnants of explosive eruptions. Bottom left: Close-up inside the red box of an explosive volcanic deposit. Top left: Details of the inside of the vent. NASA/JHUAPL/CIW

The explosive eruptions are driven by the force of expanding gas and are a surprising find on Mercury, whose proximity to the Sun was thought to have deprived it of these volatiles – the heat would have boiled them off. Scientists suspect there were actually multiple explosive eruptions, possibly spaced out over a long period of time. This means that volatile gas-forming materials (whose composition will remain uncertain until Esa’s BepiColombo mission begins operating in 2026) were repeatedly available in Mercury’s magmas.

The highest cliff?

In land regions rich in soil or vegetation, cliffs provide the greatest exposures of clean rock. Although 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 of Verona, seven kilometers high. This is a feature of Miranda, Uranus’s small moon, which is often described as “the tallest cliff in the solar system”, including on a recent Nasa website. It even goes so far as to point out that if you were careless enough to fall from the top, it would take you 12 minutes to fall to the bottom.

Images of Verona Rupes.
Verona Rupes, about 50 km long and several km high, but not as cliff-like as it looks as seen by Voyager 2 during its 1986 flyby. NASA/JPL

This is nonsense, because Verona Rupes is far from vertical. The only images we have are from Voyager 2, captured during its 1986 flyby of Uranus. outer planet) moved down against the adjacent block.

However, the obliquity of the view is misleading, making it impossible to be sure of the slope of the face – it probably tilts less than 45 degrees. If you tripped at the top, I doubt you’d even slip down. The face appears to be very smooth in the best image, but rather low resolution, but at Miranda’s daytime temperature of -170°C the water ice has high friction and is not slippery at all.

Titan’s Drowned Coast

For my final example, I could have happily chosen virtually anywhere on Pluto, but instead opted for a spellbinding Earth-like 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 the rivers of methane flowing into the sea were evidently flooded as the sea level rose. This intricately jagged coastline strongly reminds me of the Musandam Peninsula in Oman, on the southern side of the Strait of Hormuz. There, the local crust has been deformed downward due to the ongoing collision between the Arabian and Asian continents. Did something similar happen on Titan? We don’t know yet, but the way the coastal geomorphology is changing around Ligeia Mare suggests to me that its drowned valleys are more than just a result of rising liquid levels.

Rock and liquid water on Earth, freezing 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.

This article originally appeared in The Conversation

David Rothery is professor of planetary geosciences at the Open University.

Arline J. Mercier