A protective atmosphere, a friendly sun and a lot of liquid water – the earth is a special place. Using the unprecedented capabilities of the NASA / ESA / CSA James Webb space telescope, astronomers are on a mission to determine how special our original planet is. Can this temperate environment exist elsewhere, even around another type of star? The Trappist -1 system offers an enticing opportunity to explore this question, because it contains seven worlds of the size of the earth orbit around the most common star type of the Milky Way – a red dwarf.
The concept of this artist represents Trappist-1D passing in front of his turbulent star, with other members of the closely wrapped system shown in the background. Image credit: NASA / ESA / CSA / Joseph Olmsted, STSCI.
Trappist-1 is an ultracool dwarf star in the Aquarius constellation, at 38.8 light years.
The star is barely larger than Jupiter and has only 8% of the mass of our sun. He quickly turns and generates energy pushes of UV radiation.
Trappist-1 is a home of seven transit planets, named Trappist-1b, C, D, E, F, G and H.
All these planets have a size similar to the earth and in Venus, or slightly smaller, and have very short orbital periods: 1.51, 2.42, 4.04, 6.06, 9.21, 12.35 and 20 days, respectively.
They are probably all locked at the tide, which means that the same face of the planet is always pointed on the star, because the same side of the moon is always pointed on the earth. This creates a perpetual nocturnal side and a perpetual day on each Trappist-1 planet.
“In the end, we want to know if something like the environment we appreciate on Earth can exist elsewhere, and under what conditions,” said Dr. Caroline Piaulet-Ghorayeb, astronomer of the University of Chicago and the Trottier Institute for Research on Exoplanets of the University of Montreal.
“While webb gives us the opportunity to explore this question in the planets of the size of the earth for the first time, at this stage, we can exclude Trappist-1D from a list of earth twins or potential cousins.”
Dr. Piaulet-Ghorayeb and his colleagues used the Nirspec instrument from webb (near infrared spectrograph) to obtain transmission spectra from the Trappist-1D planet.
They have not detected common molecules in the earth’s atmosphere, such as water, methane or carbon dioxide.
However, they described several possibilities for the exoplanet which remain open to the follow -up study.
“There are some potential reasons for which we do not detect an atmosphere around Trappist-1D,” said Dr. Piaulet-Ghorayeb.
“It could have an extremely thin atmosphere that is difficult to detect, a bit like Mars.”
“Alternatively, it could have very thick and high altitude clouds that block our detection of specific atmospheric signatures – something more like Venus.”
“Or, it could be a sterile rock, without any atmosphere.”
Regardless of the case for Trappist-1D, it is difficult to be a planet in orbit around a red dwarf star.
Trappist-1, the host star of the system, is known to be volatile, often freeing eruptions of high energy radiation with the potential to remove atmospheres from its small planets, in particular those in orbit around the narrowest way.
Nevertheless, scientists are motivated to seek signs of atmospheres on the Trappist-1 planets because the red dwarf stars are the most common stars of our galaxy.
If the planets can keep an atmosphere here, under waves of severe stellar radiation, they could, as say, do anywhere.
“Webb’s sensitive infrared instruments allow us to immerse ourselves in the atmospheres of these smaller and colder planets for the first time,” said Dr. Björn Benneke, astronomer of the Trottier Institute for Research on Exoplanets at the University of Montreal.
“We are really starting to use webb to search for atmospheres on planets the size of a land, and to define the line between the planets that can keep an atmosphere, and those that cannot.”
The results appear in the Astrophysical Journal.
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Caroline Piaulet-Saryb and al. 2025. Strict limits on potential secondary atmospheres on the Trappist of the Timét-1D rocky earth. APJ 989, 181; Two: 10.3847 / 1538-4357 / ADF207
