MADRID, 13 (EUROPA PRESS)
The rocky, Earth-like exoplanet TRAPPIST-1 d, located in the habitable zone of its system, lacks an Earth-like atmosphere, making it difficult for liquid water to exist on its surface.
This is the conclusion of a new study of this system, 40 light-years away and with seven Earth-sized planets, conducted with the James Webb Space Telescope and published in The Astrophysical Journal.
"At this point, we can rule TRAPPIST-1 d out of the list of possible Earth twins or cousins," lead author Caroline Piaulet-Ghorayeb of the University of Chicago and the University of Montreal's Trottier Institute for Research on Exoplanets (IREx) said in a statement.
IN THE MIDDLE OF THE TEMPERATE ZONE
Because this system's star is a dim, relatively cool red dwarf, the "habitable zone"—where the planet's temperature could be ideal, allowing liquid water to exist on its surface—is much closer to the star than in our own solar system. TRAPPIST-1 d, the third planet from the red dwarf, lies on the cusp of that temperate zone; however, its distance from its star is only 2% of Earth's distance from the Sun. TRAPPIST-1 d completes one full orbit around its star, its year, in just four Earth days.
Webb's NIRSpec (Near Infrared Spectrograph) instrument did not detect TRAPPIST-1 d molecules common in Earth's atmosphere, such as water, methane, or carbon dioxide. However, Piaulet-Ghorayeb described several possibilities for the exoplanet that remain open for follow-up studies.
There are several possible reasons why we don't detect an atmosphere around TRAPPIST-1 d. It could have an extremely thin, difficult-to-detect atmosphere, similar to that of Mars. It could also have very dense clouds at high altitudes that prevent the detection of specific atmospheric signatures, something more like Venus. Or it could be a barren rock, with no atmosphere at all, Piaulet-Ghorayeb said.
A VOLATILE STAR
Whatever the case with TRAPPIST-1 d, it's hard to be a planet orbiting a red dwarf star. TRAPPIST-1, the system's host star, is known for its volatility, often releasing flashes of high-energy radiation with the potential to strip its smaller planets, especially those orbiting closer.
However, scientists are motivated to look for signs of atmospheres on the TRAPPIST-1 planets because red dwarf stars are the most common stars in our galaxy. If planets manage to maintain an atmosphere here, under waves of intense stellar radiation, they could, as the saying goes, reach anywhere.
Webb's observations of TRAPPIST-1's outer planets continue. For one thing, planets e, f, g, and h might be more likely to have atmospheres because they are farther from their host star's energetic outbursts. However, their distance and colder environment will make atmospheric signatures difficult to detect, even with the Webb telescope's infrared instruments.
"All hope is not lost for the atmospheres around the TRAPPIST-1 planets," Piaulet-Ghorayeb said. "While we didn't find a large, defined atmospheric signature on planet D, there's still a possibility that the outer planets contain a lot of water and other atmospheric components."
