2023-06-20 10:16:00
Contrary to expectations, the second exoplanet in the particularly interesting TRAPPIST-1 star system does not have a dense atmosphere either. This was determined by a research group led by Sebastian Zieba from the Max Planck Institute for Astronomy using the James Webb space telescope. He now explains that one was actually hoping for a celestial body that, like Venus, is surrounded by a dense and hot atmosphere. But that can definitely be ruled out. Instead, it probably has an atmosphere as dense as Earth at most, but it is also possible that it is a purely rocky planet without any significant gas envelope. However, even the ultra-modern space telescope has reached its limits in the attempt to prove it.
First expectations disappointed
So far, seven rocky planets have been discovered around the red dwarf star TRAPPIST-1, on which even liquid water seemed to be possible. However, only the three exoplanets TRAPPIST-1e, f and g are in the so-called habitable zone of the star. On the innermost two, which are still the easiest to explore, conditions like those on Venus were expected, i.e. a much denser atmosphere than on Earth. For this, the exoplanets orbiting extremely close to their star would have had to retain these gas shells over a long period of time, despite the intense stellar winds and intense UV radiation. Their comparatively large mass could have helped, says Zieba. With TRAPPIST-1b the hope had already been dashed, it resembles Mercury.
Although the amount of radiation TRAPPIST-1c receives from its star closely matches that of Venus, it too has failed to hold what may have been a previously dense atmosphere, the team writes. The data obtained are inconsistent with any kind of thick gas envelope that is rich in carbon dioxide and has more than ten times the pressure of Earth. However, a wide range of oxygen-carbon dioxide mixtures with a pressure between one and 100 percent of the value at sea level is still possible. So while it’s not currently possible to pinpoint this any further, there is hope that sufficiently heavy rocky planets can maintain an atmosphere for a sufficient period of a star’s lifetime.
Image 1 of 12 The planets of TRAPPIST-1 compared to some in the solar system
(Bild: NASA/JPL-Caltech/R. Hurt, T. Pyle (IPAC))
However, the data would also match a planet made of bare rock and with a weathered surface, Zieba restricts this directly. Even with what is undoubtedly the most powerful space observatory of all time, it is simply too difficult to capture the heat signature and traces of a possible atmosphere. Nevertheless, the space telescope should carry out further observations and, if possible, find out whether there is an atmosphere there. The team believes that the Extremely Large Telescope (ELT) of the European Southern Observatory could possibly provide the decisive clue. This is currently being built in Chile and is scheduled to go into operation by the end of the decade. Your analysis of TRAPPIST-1c present them in the journal Nature.
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