Alien volcanos
Fred Watson
Fred Watson
However, you might be surprised to know that Earth is not alone in having volcanoes – in fact, it’s beaten numerically by the planet Venus, whose surface is pockmarked with more than 1600 of them. But Venus’s opaque atmosphere makes it hard to establish whether any of them are still active.
When it comes to active volcanoes, Jupiter’s moon Io takes the crown. Violent eruptions on this distant world have been observed for many years, and its entire surface is being renewed constantly by lava from its 400 or so active vents. The heat source for these volcanoes is the gravitational squeezing and stretching of Io by Jupiter, which it orbits 350,000km above the giant planet’s cloud tops.
So if volcanoes are relatively common in our solar system, what might we find among the 5800 or so known planets of other stars?
Most exoplanets are so distant from our solar system that their existence can only be demonstrated by careful observation of their parent stars. And the most successful way of finding them is to look for dips in the light of the star as an orbiting planet passes in front of it – a so-called transit. If the dip is repeated periodically, it’s being caused by a transiting planet.
But this technique can offer more information. If the planet is a rocky world with a surrounding atmosphere, the parent star’s light is imprinted with a chemical signature in its rainbow spectrum as it passes through the planet’s atmosphere during a transit. That signature is a telltale indicator of the chemical make-up of the planet’s atmosphere.
Now, let me introduce L 98-59 d, an exoplanet some 35 light-years from our solar system. It was discovered by the transit technique back in 2019 but is now the subject of measurements by a team of UK, US and European astronomers using the James Webb Space Telescope. For the first time, sulphur compounds (specifically hydrogen sulphide and sulphur dioxide) have been discovered in its atmosphere.
These are highly suggestive of volcanic activity, which tallies with the expected Io-like gravitational heating of the planet due to its very short ‘year’ of 7.5 Earth days. If confirmed by subsequent observations, L 98-59 d will be the first-known geologically active exoplanet.
