JWST observations are consistent with the planet TRAPPIST-1e having an atmosphere, two new papers report. The results don’t mean an atmosphere is definite, let alone tell us if it has a composition suited to habitability, but it’s a major step forward in the search for worlds like Earth. Given TRAPPIST-1e’s location firmly within its star’s habitable zone, a substantial atmosphere would make the presence of liquid water at the surface likely.
When the TRAPPIST-1 system was discovered, astronomers could barely contain their excitement. Here was a system where five (later raised to seven) planets of similar size to the Earth not only orbited a star, but regularly transited across its face from our perspective, allowing us to see them in silhouette. Moreover, three lie in the system’s habitable zone.
At the time, we lacked the capacity to seek signs of atmospheres during these passes, but everyone knew that when the JWST finally got into space, it would be much better suited to the task. Even with the system a relatively close 40 light-years away, the JWST can’t collect enough data to determine if an atmosphere is present based on a single transit. By stacking the data from multiple transits together, however, it was hoped we would soon know if these worlds had air.
TRAPPIST-1 has the advantage for research purposes of being a faint red dwarf, which means these planets orbit close by, even those in the habitable zone, so transits occur frequently. Combining data from four transits has raised the hopes of researchers, but they still can’t be sure.
Light collected in these transits is reduced at certain wavelengths, exactly what the team were looking for. Nevertheless, Dr Ryan MacDonald of the University of St Andrews said in a statement: “We are seeing two possible explanations. The most exciting possibility is that TRAPPIST-1e could have a so-called secondary atmosphere containing heavy gases like nitrogen. But our initial observations cannot yet rule out a bare rock with no atmosphere.”
If you’re wondering why the results aren’t clear, it’s because starspots can have similar effects on the light spectrum detected. Starspots come and go, so if we keep observing TRAPPIST-1e long enough and the spectrum collected doesn’t change, the chance of an atmosphere will increase to near certainty.
This may sound as if little has happened so far, but the team have excluded some possibilities, such as an atmosphere dominated by molecular hydrogen. They also find a Venus-like, carbon dioxide-rich atmosphere unlikely, but not impossible. In other words, if TRAPPIST-1e does have an atmosphere, it’s most likely more like Earth’s than the other members of the Solar System.
A comparison of the spectrum collected during transits and models with a nitrogen-rich atmosphere (blue) and no atmosphere (orange).
Image credit: NASA, ESA, CSA, J. Olmsted (STScI)
“In the coming years we will go from four JWST observations of TRAPPIST-1e to nearly twenty, we finally have the telescope and tools to search for habitable conditions in other star systems, which makes today one of the most exciting times for astronomy,” MacDonald said.
The downside of TRAPPIST-1’s low luminosity, which makes for practical observing times, is that its planets are exposed to more flares than those that get similar amounts of light orbiting a larger star. It’s feared these flares could strip planets of any atmospheres they may once have had.
Those fears were realized when it came to observations of TRAPPIST-1b and c, and later d, which have little to no atmosphere. As the hottest planets in the system, these were never candidates for life. Being more exposed to flares also meant they would be likely to be the first to lose their atmospheres, but it was still not a good sign for those further out.
If a nitrogen-rich atmosphere is confirmed for TRAPPIST-1e, it will not only intensify the hunt for signs of oxygen or other gases that might hint at life, but it will also indicate that red dwarfs are not all atmosphere-killers.
Some teams expected they would need more than four transits of TRAPPIST-1e to get useful results, but MacDonald and co-authors used longer wavelengths than previous efforts to gain extra confidence.
The JWST has studied the atmospheres of gas giants, but these were considered mainly practice runs for the harder task of finding atmospheres around Earth-like worlds, since there’s no real chance of life there. There have also been observations of planets smaller than Neptune, including carbon-rich molecules. These have inspired fevered headlines about signs of life, but most astronomers have been skeptical.
TRAPPIST-1e has 69 percent of Earth’s mass and would have a very similar temperature, provided it can match Earth’s greenhouse effect.
The two studies are published in The Astrophysical Journal Letters, here and here.
Source Link: Earth 2.0? Hints Of First Atmospheric Detection Around An Earth-Like Planet Orbiting Another Star
