JWST hints at fewer habitable planets

For the second time, the James Webb Space Telescope (JWST) has searched and failed to find a thick atmosphere on an exoplanet in One of the most exciting planetary systems known. Astronomers report¹ Today, TRAPPIST-1 c may not have a tantalizing atmosphere, just as they reported months ago for its neighbor TRAPPIST-1 b.

There remains a chance that some of the other five planets in the TRAPPIST-1 system may have thick atmospheres containing geologically and biologically interesting compounds such as carbon dioxide, methane, or oxygen. But the two planets studied so far appear to have no or almost no atmosphere.

Since planets of this type are common around many stars, “it would certainly reduce the amount of planets that might be habitable,” says Sebastian Zippa, an exoplanet researcher at the Max Planck Institute for Astronomy in Heidelberg, Germany. He and his colleagues describe the discovery in nature.

Star power system

All seven TRAPPIST-1 planets, which orbit a star about 12 parsecs (40 light-years) from Earth, have rocky surfaces and roughly the size of Earth. Astronomers consider the system one of nature’s best laboratories for studying how planets form, evolve, and potentially become habitable. Planets are a prime target for JWST, which launched in 2021 and is powerful enough to explore their atmospheres in greater detail than other observatories such as the Hubble Space Telescope.

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The planet’s host star is a cool, faint star known as an M dwarf, which is the most common type of star in the Milky Way. They release large amounts of ultraviolet radiation, which can erode any nearby planet’s atmosphere.

The innermost planet of the system, TRAPPIST-1 b, is blasting with four times the amount of radiation Earth receives from the sun, so it came as no surprise when JWST discovered it didn’t have much of an atmosphere.². But the next in line, TRAPPIST-1 c, orbits farther from its star, and it seems possible that the cooler planet might have managed to hang on to more atmosphere.

Ziba’s team pointed the JWST at the TRAPPIST-1 system four times during October and November, allowing scientists to calculate that the surface temperature of TRAPPIST-1 c, on the side facing its star, registers at about 107 degrees C – too hot to maintain a temperature its surface temperature. A dense atmosphere rich in carbon dioxide.

Low water mark

By comparing the observations with models of the planet’s potential chemistry, the scientists also concluded that TRAPPIST-1 c would have had very little water when it formed — less than a dozen oceans of ocean water. Together, the low amount of water when the planet was born and the lack of carbon dioxide in the thick atmosphere today indicate that TRAPPIST-1 c never had many habitable components.

But there may still be hope for other planets in the system. in paper³ Posting June 8 on arXiv’s preprint server, Joshua Chrissansen-Tuton, a planetary scientist at the University of Washington in Seattle, announces that the TRAPPIST-1 planets e and f — the fourth and fifth dimensions from the star — may still have an atmosphere as thick as possible. Atmospheric, because they sit far enough from the star to avoid having all their water blown away, unlike planets B and C.

In other words, what scientists find on planets B and C may not say much about what exoplanet atmospheres might look like. “I think it makes sense to remain neutral about the possibilities of exoplanets retaining atmospheres,” says Chrisansen Totton.