Also not an Earth twin: exoplanet TRAPPIST-1d without an Earth-like atmosphere
With seven rocky planets, the planetary system of TRAPPIST-1 is one of the most exciting of all. Now another one has turned out not to be Earth-like.
Artistic representation of TRAPPIST-1d
(Image: NASA, ESA, CSA, J. Olmsted (STScI)/CC BY 4.0 INT)
The exoplanet TRAPPIST-1d does not have an Earth-like atmosphere either, but hostile gas envelopes such as those known from Mars or Venus are still possible. This is the result of new measurements with the James Webb space telescope. They now confirm that TRAPPIST-1d is not a potential Earth twin or cousin either, as study leader Caroline Piaulet-Ghorayeb now explains. The exoplanet lies at the boundary of the so-called habitable zone of its star; theoretically, liquid water and thus the most important prerequisite for Earth-like life would be possible on its surface. “Thanks to Webb, we now know that TRAPPIST-1d is far from being a habitable world. Now we've learned that Earth in space is even more special,” says co-author Ryan MacDonald about the analysis.
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TRAPPIST-1 is 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, the largest number we know of in any other planet. However, only TRAPPIST-1e, f, and g lie in the habitable zone, but because the three are comparatively far away from the star, they are particularly difficult to study. The inner planets, including Trappist-1d, are easier to study. Before no evidence of an Earth-like atmosphere was discovered, hopes of such a gas envelope had already been dashed in the case of TRAPPIST-1 b and c. According to Piaulet-Ghorayeb, there is still the possibility that the next three exoplanets contain a lot of water and other substances that we know from Earth.
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The search for traces of a possible Earth-like atmosphere on TRAPPIST-1d has now been carried out using the NIRSpec (Near-Infrared Spectrograph) instrument of the ultra-modern space telescope. Traces of water, methane, carbon dioxide, and other substances were not found. An extremely thin atmosphere like that of Mars or a thick gas shell with clouds at high altitudes, as we know it from Venus, are also conceivable. But it could also be barren rock without any atmosphere, says Piaulet-Ghorayeb. In any case, the analysis confirms that it is difficult for a planet to form around a red dwarf star like TRAPPIST-1, as its strong radiation can strip exoplanets of their atmosphere.
Red dwarfs are by far the most common stars in the universe, and the search for exoplanets is also successful there. However, because the stars are comparatively small, the so-called habitable zone is particularly close to these celestial bodies. Just last fall, a research group explained that this does not necessarily mean that any atmospheres that may form are quickly removed. Simulations had shown that rocky planets could be able to form and retain a stable atmosphere despite the immense radiation from the most common class of stars in the universe. This could be enough time for life to develop after all.
(mho)
