Space

Venus has very few volcanoes – weirdly, this might be why it’s as hot as hell

In the quest to discover habitable planets, scientists look for qualities similar to those of Earth. We do this because Earth sustains life, of course, but it falls down when you consider Venus. Based on size, chemistry and position in the solar system, our neighbouring planet is the most Earth-like ever observed. Yet while Earth is the definition of habitable, the planet Venus is a barren, hot, hellish wasteland.

Geologists like myself are trying to understand why two almost identical planets became so different. This is one way we can assist the astrophysics community in the exciting hunt for habitable exoplanets. A key part of the puzzle is understanding the interplay between plate tectonics and volcanoes, since this governs the chemistry of the air that supports life.

I have been part of a research collaboration to look at Venus’ volcanic history, the results of which have just been published in the journal Physics of the Earth and Planetary Interiors. This study sheds some valuable light on the volcanic history of Earth’s sibling, and indirectly speaks towards how Venus became so hot in the first place.

The starting point to understanding Venus is the climate. The average surface temperature is 460℃ – far too hot for liquid water and above the known thermal limit for life, which is roughly 122℃.

This extreme heat is not simply because Venus is closer to the Sun, but also because it is enveloped by an über-greenhouse atmosphere. At 92 times the pressure of that on Earth, it’s enough to crush modern submarines. If you were standing on the Venusian surface it would be like swimming 1,000 metres below sea level – if the oceans were 460℃, that is.

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It ain’t half hot, mum. Andrea Izzotti

The scorching temperature of Venus’s surface has many knock-on effects. It means, for example, that there’s no Earth-like plate tectonics. Most of the crust is too soft to snap, and it “heals” when broken. There have recently been suggestions that the planet might either have its own alternative version of plate tectonics, or that the high surface temperature results in the Venusian crust being physically decoupled from mantle flow beneath. At any rate, where plate tectonics is behind 90% of volcanic eruptions on Earth, this is not the case on Venus.

Venus does have volcanoes, but they’re all of the variety we call intra-plate or hotspots, where plumes of magma rise up from the mantle and push their way to the surface via cracks in the crust. To study them, we compared them to the ones on Earth. We only considered volcanoes situated on Earth’s oceanic crust, since it is more comparable to the Venusian crust.

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Kilauea in Hawaii, one of Earth’s hotspot volcanoes. Wikimedia

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