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- Rocky planets orbiting red dwarf stars appear to be fairly common. Can any of them have atmospheres and support life?
- The seven Earth-sized planets of TRAPPIST-1 are the subject of a new study focusing on their atmospheres. Observations show the two innermost planets have likely lost all or most of their atmospheres.
- But some of the planets farther out from the star could still have atmospheres, the new study said.
The atmospheres of the TRAPPIST-1 exoplanets
Rocky planets seem to be quite common in our galaxy, based on discoveries in recent years. So far, astronomers have found most of them orbiting red dwarf stars, the most common type of star in the Milky Way. As of now, observations suggest the closest rocky planets to these stars have little to no atmospheres due to intense ultraviolet (UV) radiation. But planets farther out, especially in the habitable zone, might fare better. On October 23, 2024, a team of scientists said some of the seven Earth-sized planets in the TRAPPIST-1 system might have stable atmospheres.
The study results can also be extrapolated to other rocky planets around red dwarf stars.
The researchers published their peer-reviewed results in Nature Communications on September 27, 2024.
Dangerous conditions for red dwarf planets
Overall, the conditions around red dwarf stars are not ideal for habitable planets. Red dwarfs are smaller than our sun but emit intense ultraviolet radiation. For rocky planets orbiting closest to them, this is not good. The radiation can strip away atmospheres and water, leaving the planets’ surfaces desiccated and uninhabitable.
Indeed, NASA’s Webb space telescope has found that the inner two planets around TRAPPIST-1 – TRAPPIST-1 b and TRAPPIST-1 c – seem to have little to no atmosphere left. Which isn’t too surprising. Previous studies indicated this was likely to be the case. But for the prospects of potentially habitable planets around TRAPPIST-1, scientists have been most interested in the planets farther out from the star, TRAPPIST-1 e in particular. Some studies have suggested it and maybe some of the other outer planets could still have atmospheres. Now, the new study from the University of Washington supports that possibility.
TRAPPIST-1 e is just slightly smaller than Earth, with a mass about 70% of Earth’s. It orbits in the middle of its star’s habitable zone. That’s the region where temperatures could allow liquid water to exist.
Some TRAPPIST-1 exoplanets could have stable atmospheres
The study found that some rocky exoplanets around red dwarfs could hold onto stable atmospheres. Lead author Joshua Krissansen-Totton at the University of Washington said:
One of the most intriguing questions right now in exoplanet astronomy is: Can rocky planets orbiting M-dwarf stars maintain atmospheres that could support life? Our findings give reasons to expect that some of these planets do have atmospheres, which significantly enhances the chances that these common planetary systems could support life.
Webb is still observing the TRAPPIST-1 system, which is 40 light-years from Earth. To date, it has preliminarily characterized the inner two planets, b and c. The data suggest that both planets either have no atmospheres or very tenuous ones at best. Astronomers have not yet published any tentative results from the other five planets. Being farther out from the star, those planets are a bit more difficult for Webb to analyze. As Krissansen-Totton explained:
It’s easier for the Webb telescope to observe hotter planets closest to the star because they emit more thermal radiation, which isn’t as affected by the interference from the star. For those planets we have a fairly unambiguous answer: They don’t have a thick atmosphere. For me, this result is interesting because it suggests that the more temperate planets may have atmospheres and ought to be carefully scrutinized with telescopes, especially given their habitability potential.
More observations needed
Determining whether any of the other TRAPPIST-1 planets have atmospheres – and could be potentially habitable – will require more telescope observations. There are a handful of other rocky exoplanets that Webb and other pending telescopes can look at closer. According to Krissansen-Totton:
With the telescopes that we have now, the James Webb and the extremely large ground-based telescopes coming soon, we’re really only going to be able to look at a very small number of habitable zone rocky planets’ atmospheres. It’s the TRAPPIST-1 planets and a couple of others. Given the huge interest in the search for life elsewhere, our result suggests that it’s worthwhile investing telescope time to continue studying the habitability of these systems with the technology we have now, rather than waiting for the next generation of more powerful telescopes.
On October 16, 2024, scientists at the SETI Institute and Penn State University said they’ve been searching for signs of alien radio communications between the seven exoplanets in the TRAPPIST-1 system. They used the Allen Telescope Array in California, which is dedicated to the Search for Extraterrestrial Intelligence (SETI).
They didn’t find any confirmed signals of alien origin, but said they will continue to refine the new techniques used and use larger telescopes in subsequent searches.
Bottom line: Some of the rocky TRAPPIST-1 exoplanets could still have atmospheres, a new study from the University of Washington suggests. Could they even be habitable?
Source: The erosion of large primary atmospheres typically leaves behind substantial secondary atmospheres on temperate rocky planets
Via University of Washington
Read more: 1st TRAPPIST-1 results from Webb Space Telescope
Read more: Are the TRAPPIST-1 exoplanets habitable, or not?