The conclusions of Caroline Piaulet-Ghorayeb and her team are clear: Trappist-1 D, the third planet around the small Star Trappist-1, has no atmosphere similar to that of the earth.
These are observations made with the space telescope James-Webb (JWST) which allowed scientists to learn more about the nature of this rocky planet. Despite its size analogous to that of the earth and its position, near the border of the temperate zone of its star (where liquid water could theoretically exist), the data show that this planet is not a land 2.0.
“What we want to know ultimately is if an environment like that of the earth can exist elsewhere and under what conditions,” explains Caroline Piaulet-Ghorayeb, a graduate of the University of Montreal and now a postdoctoral researcher at the University of Chicago. The telescope James-Webb Finally allows us to ask the question for planets of terrestrial size. And already, we can scratch Trappist-1 D from the list of worlds that could resemble ours. ”
These works, published in The Astrophysical Journal Today, were started by the researcher during her doctorate in astrophysics at Udem, at the Institut Trottier de Research on exoplanets (IREX).
At 40 light years
Caroline piaulet-slaryb
Credit: courtesy
The planetary system of Trappist-1, a red dwarf star located at 40-light years from Earth, was revealed in 2017. It holds the record for the largest number of rocky planets of terrestrial size known in a single star: seven in total.
The Trappist-1 star is much less bright and much colder than the sun. The temperate area of the system, the region where a planet could keep liquid water on the surface, is therefore much closer to the star than in our solar system.
The Planet Trappist-1 D is only two percent of the distance between the earth from the sun and performs an entire orbit around its star every four terrestrial days (while the earth does it in 365 days). It is just far enough to be in this area, sometimes called “habitable”.
With the JWST Nirspec infrared spectrograph, The team of astronomers has not detected on Trappist-1 D molecules such as water, methane or carbon dioxide, which are abundant in the atmosphere of the earth.
Scientists also dismissed the possibility of an atmosphere rich in methane which is nevertheless found on the rocky bodies of the solar system like Titan, a moon of Saturn.
According to Caroline Piaulet-Ghorayeb, other scenarios remain to be studied: “There are several reasons which may explain why we have not detected an atmosphere around Trappist-1 D,” she says. This planet could have a tenuous atmosphere, difficult to detect, a bit like on Mars. It could also, like Venus, be wrapped in very thick and high altitude clouds, which block the signature of certain gases. Or, this planet could be completely devoid of atmosphere. ”
A turbulent star
It is not easy to be a planet in orbit around a red dwarf like Trappist-1. This star is known to be very active, which quite complicates the study of his planets, as demonstrated in 2023 a study carried out by Olivia Lim, doctoral student at Irex. Frequent very energetic eruptions occur, capable of blowing the atmosphere of its small planets, especially those which are near it.
However, scientists persist in looking for traces of atmosphere around the planets of this system, because the red dwarf stars are the most abundant in our galaxy. If we can prove that planets manage to keep their atmosphere despite these hostile conditions, this will open the door to the possibility of habitable environments elsewhere, in more favorable contexts.
“Sensitive infrared instruments of the telescope James-Webb allow us for the first time to examine the atmosphere of these little colder planets, explains Björn Benneke, member of the IREX and co -author of the study. We are barely starting, thanks to his sophisticated instruments, to explore the atmospheres of these planets, to understand which can keep their atmosphere and which are incapable of it. ”
Other planets to study
The observations made with the JWST continue for the planets E, F, G and H, the most distant from Trappist-1. These planets represent promising targets, but they also pose several challenges to astronomers. On the one hand, according to Björn Benneke, these planets are more likely to have atmospheres because they are more distant from their active star. However, this same distance will make their signatures more difficult to detect with the infrared instruments of James-Webb.
“We must not lose hope of finding atmospheres around the other planets of Trappist-1,” concludes Caroline Piaulet-Ghorayeb. Even if we have not found a strong atmospheric signature on Trappist-1 D, it is still possible that the more distant planets contain water or certain elements in their atmosphere which would inform us about their habitability. ”
About this study
The article “Strict limits on potential secondary atmosphere on the temperate rocky exo-erh trappist-1 d” is published today in the journal The Astrophysical Journal. In addition to Caroline Piaulet-Ghorayeb and Björn Benneke, the team includes Keavin Moore, Pierre-Alexis Roy, Olivia Lim, René Doyon, Loïc Albert, Michael Radica (today at the University of Chicago), Louis-Philippe Coulombe, David Lafrenière, Nicolas B. Cowan, Alexandrine L’Heureux, Romain Allart, (today at the University of Waterloo), Stefan Pelletier (today at the University of Geneva) and Jason F. Rowe, of IREX, the three students who were mentored by Caroline Piaulet-Ghorayeb in the context of initianceccolands and six other co-authors of Canada, the United States, the United Kingdom, Switzerland and France.
