Is this a volcanic exoplanet? Hints are in its atmosphere
- L 98-59 d is a super-Earth exoplanet, discovered in 2019. It’s 35 light-years away and about 1.5 times the size of Earth.
- The Webb space telescope observed the planet again recently, looking for evidence of an atmosphere.
- It found the planet has a sulfur-rich atmosphere, the new results suggest. Astronomers said it might be an active volcanic world, with volcanoes reminiscent of those on Jupiter’s volcanic moon Io.
Is this a volcanic exoplanet?
Volcanoes are common in our solar system. Earth, Mars and Venus all have them. Even some moons do, for example, Jupiter’s moon Io. But what about distant exoplanets around other stars? On November 11, 2024, researchers at The Open University in the U.K. said they’ve found possible evidence for a sulfur-rich atmosphere on a planet 35 light-years away. The planet is labeled L 98-59 d. It’s about 1.5 times the size of Earth. The researchers tentatively detected the gases sulfur dioxide (SO2) and hydrogen sulfide (H2S) in its atmosphere. If confirmed, it would indicate the surface is likely molten or volcanic. Exoplanet L 98-59 d would also be the smallest of the distant planets known so far that have confirmed atmospheres.
The researchers used NASA’s Webb Space Telescope to make the discovery.
Researcher Agnibha Banerjee at The Open University wrote about the new findings in The Conversation on November 11, 2024.
The researchers published their peer-reviewed findings in The Astrophysical Letters on October 30, 2024.
Meet L 98-59 d
L 98-59 d is a rocky planet, like Earth, and about 1.5 times the size of Earth. This puts it in the category of super-Earth. It orbits an M-type star – or red dwarf – 35 light-years from Earth. NASA’s Transiting Exoplanet Survey Satellite (TESS) space telescope discovered it in 2019.
TESS used the transit method to detect the planet. That’s when a planet transits – passes in front of – its star, as seen from Earth. L 98-59 d orbits close to its star, completing an orbit in only 7.5 days.
"Researchers, including academics from The Open University (OU) have discovered a possible sulphur-rich atmosphere of exoplanet L 98-59 d, signalling possible volcanoes on its surface."
Read more on #OUNews!https://t.co/wamVZwC1gs pic.twitter.com/SlLf4gYxvP
— Faculty of STEM, The Open University (@OU_STEM) November 2, 2024
A volcanic exoplanet with a sulfur-rich atmosphere?
Banerjee and colleagues used NASA’s Webb Space Telescope to observe one transit of the planet. As the planet passed in front of the star, Webb tried to detect an atmosphere. It did so by analyzing the transmission spectrum of the planet. That is where some light is absorbed by the atmosphere and some is transmitted through it. In the spectrum, the dark lines and dim bands of light correspond to atoms and molecules in the planet’s atmosphere. And, indeed, the analysis showed evidence of a possible atmosphere, more specifically an atmosphere filled with sulfur dioxide and hydrogen sulfide. The paper stated:
The atmospheric spectrum indicates the possible presence of the sulfur-bearing species H2S and SO2, which could hint at active volcanism on this planet if verified by future observations.
What does that mean?
A volcanic world, but not like Earth
The discovery of those two gases suggests L 98-59 d is likely a volcanic or molten world. However, it would be unlike any of the planets in our solar system that have volcanoes. Earth, of course, has many active volcanoes. In addition, there is growing evidence that Venus’ volcanoes are still active as well. And there are huge volcanoes on Mars, although they have been dead or dormant for millions to billions of years. But Earth’s atmosphere is dominated by nitrogen, while the atmospheres of Venus and Mars are mostly carbon dioxide.
An Io-like world?
So, this means the volcanic processes on L 98-59 d are likely quite different. In fact, they might be more similar to Jupiter’s moon Io, which is the most volcanically active body in our solar system. On Io, tidal heating drives volcanism. Jupiter’s immense gravity pulls and squeezes Io, heating it on the inside.
As a result, Io’s insides are constantly melting and spewing out through volcanoes. This may be similar to L 98-59 d, because it orbits so close to its star.
If L 98-59 d is truly volcanically active, and in a way not seen on rocky planets in our own solar system, that would be exciting for planetary scientists. It would be a chance to get a glimpse of volcanic processes not seen on planets before. As the paper noted:
The rocky planets in the solar system all have different atmospheric compositions, and the study of such atmospheres in exoplanetary systems could unlock a rich diversity of unexplored chemistries.
Bottom line: L 98-59 d, a super-Earth 35 light-years away, may be a volcanic exoplanet. NASA’s Webb space telescope has detected a possible sulfur-rich atmosphere.
Read more:
Is there a volcanic exomoon orbiting this giant exoplanet?
Wow! New volcano on Jupiter’s moon Io
Active Venus volcanoes revealed again in Magellan data
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