Exoplanet: Earth-like atmosphere still possible after analysis of TRAPPIST-1e

The exoplanet TRAPPIST-1e has apparently lost its primary atmosphere, but it is still possible that it has built up a secondary one like our Earth and is therefore actually very similar to Earth. This has been revealed by precise analyses with the James Webb Space Telescope, the results of which have now been presented. Accordingly, it is now unlikely that the celestial body has a gas shell similar to the thick one of Venus or the thin one of Mars. However, others are still possible. But it also cannot be ruled out that it is a rocky planet with no atmosphere at all. The probability of both is about the same. This underlines how difficult the exploration is and should only increase interest in TRAPPIST-1e.

It's getting more and more interesting

TRAPPIST-1 is just 40 light-years away from Earth, and its planetary system is one of the most interesting of all because it consists of seven rocky planets. We don't know of so many in any other system. TRAPPIST-1e, f, and g are located in the habitable zone—where liquid water would in principle be possible on the surface. However, because the three are comparatively far away from the star, their exploration is particularly difficult. The inner planets are easier to study, but hopes of a gas envelope have already been dashed for TRAPPIST-1b and c. TRAPPIST-1d also has no Earth-like atmosphere; only hostile atmospheres like those of Venus or Mars are possible there. The analysis now presented brings the first of the most interesting planets there into focus.

As the US space agency NASA summarizes, data on a total of four transits, i.e., passages of TRAPPIST-1e in front of its star, were collected for the two studies. A small part of its light then passed through the direct vicinity of the exoplanet. The signal could therefore conceal traces of a possible atmosphere. However, the analysis is extremely difficult, partly because traces that can be traced back to the star itself have to be separated from those of the exoplanet. Using a new approach, a research group has now separated the variations that appeared during each transit from those that would have differed in each case, explains the Massachusetts Institute of Technology. This was an attempt to obtain data on the planet itself.

Even if the procedure did not reveal any findings on the structure of a possible atmosphere—and could not even rule out the possibility that there might not even be one—it is still a step forward. The team explains that they were able to rule out the existence of a gas envelope dominated by carbon dioxide. A gas envelope rich in nitrogen, such as that found on Saturn's moon Titan—or Earth—in the solar system, is still possible. Oceans of various shapes and sizes could also still exist on TRAPPIST-1e. However, the team points out that all exoplanets of TRAPPIST-1 always show the same side to their star. There is therefore one half with a perpetual day side and one with a night side. This would have consequences for possible bodies of water.

Further observations planned

The work now published in the Astrophysical Journal Letters represents a significant milestone in the search for life-friendly conditions on other worlds, explains the Scottish University of St. Andrews. For more than a year, the measurement data was carefully corrected to separate the signals from the star and those from the exoplanet. The fact that TRAPPIST-1e could have a secondary atmosphere is the most exciting possibility remaining after the analysis. The James Webb Space Telescope is to observe further transits in the coming years. Instead of four, data on almost 20 will ultimately be available, from which the researchers hope to gain better insights.

(mho)