The soft exoplanet LHS 1140 b could be a completely icy world (left) similar to Jupiter’s moon Europa, or it could be an ice world with a liquid subnodal ocean and a cloudy atmosphere (center). LHS 1140 b is 1.7 times the size of our planet Earth (right) and is the most promising habitable zone exoplanet yet found in the search for liquid water beyond the Solar System. Credit: Benoit Gougeon, Université de Montréal
A team of astronomers has made an exciting discovery about the temperate zones exoplanets LHS 1140 b: could be a promising “super-Earth” covered in ice or water.
LHS 1140 b, once thought to be a mini-Neptuneis now considered a possible super-Earth with a nitrogen-rich atmosphere, as suggested by The James Webb Space Telescope data. Located in the habitable zone, it may have favorable conditions for liquid water, making it a key focus for future astrobiological studies.
When it was first discovered, astronomers speculated that the exoplanet LHS 1140 b might be a mini-Neptune. This means it would be an essentially gaseous planet, but very small in size compared to Neptune. However, after analyzing data from the James Webb Space Telescope (JWST) collected in December 2023 – combined with previous data from other space telescopes such as Spitzer, Hubble and TESS – scientists have come to a very different conclusion.
Located about 48 light-years from Earth in the constellation Cetus, LHS 1140 b appears to be one of the most promising exoplanets in its star’s habitable zone, potentially harboring an atmosphere and even a liquid water ocean. The results of this discovery by Université de Montréal astronomers are available on ArXiv and will soon be published on of Astrophysical Journal Letters.
As the most advanced space telescope to date, the James Webb Space Telescope excels at studying exoplanets. Its cutting-edge technology allows astronomers to probe the atmospheres of distant worlds, analyzing their composition and assessing their potential to support life. Credit: Northrup Grumman
An exoplanet in the “Goldilocks” zone
LHS 1140 b, an exoplanet orbiting a tiny red dwarf star about one-fifth the size of the Sun, has fascinated scientists because it is one of the closest exoplanets to our Solar System that lies within the habitable zone of his star. Exoplanets found in this “Golden Zone” have temperatures that would allow water to exist on them in liquid form – liquid water is an essential element for life as we know it on Earth.
Earlier this year, researchers led by Charles Cadieux, a Ph.D. student at UdeM’s Trottier Institute for Exoplanet Research (iREx) supervised by Professor René Doyon, reported new mass and radius estimates for LHS 1140 b with extraordinary accuracycomparable to those of the well-known TRAPPIST-1 planets: 1.7 times the size of Earth and 5.6 times its mass.
Charles Cadieux, Ph.D. student at the Trottier Institute for Exoplanet Research and the Université de Montréal, is the paper’s lead author. Credit: Courtesy
One of the critical questions about LHS 1140 b was whether it is a mini-Neptune-type exoplanet (a small gas giant with a thick hydrogen-rich atmosphere) or a super-Earth (a rocky planet larger than Earth). . This latter scenario included the possibility of a so-called “Hycean world” with a global liquid ocean enveloped by a hydrogen-rich atmosphere, which would exhibit a distinct atmospheric signal that could be observed using the powerful Webb telescope.
New insights from the Webb data
Through an extremely competitive process, the team of astronomers won “discretionary director time” (DDT) on Webb last December, during which two transits of LHS 1140 b were observed with the NIRISS (Near Infrared Imaging and Slitless Spectrograph ) built by Canada. instrument. This DDT program is only the second dedicated to the study of exoplanets in Webb’s nearly two years of operations, underscoring the importance and potential impact of these findings.
Analysis of these observations strongly ruled out the mini-Neptune scenario, with compelling evidence suggesting that the exoplanet LHS 1140 b is a super-Earth that may even have a nitrogen-rich atmosphere. If this result is confirmed, LHS 1140 b would be the first soft planet to show evidence of a secondary atmosphere, formed after the planet’s initial formation.
Estimates based on all the collected data reveal that LHS 1140 b is less dense than expected for a rocky planet with an Earth-like composition, suggesting that 10 to 20 percent of its mass may be consists of water. This discovery indicates that LHS 1140 b is an imposing water world, likely resembling a snowball or ice planet with a possible liquid ocean at the subnodal point, the area of the planet’s surface that would always face the system’s host star due to the expected synchronous rotation of the planet (like Earth’s Moon).
René Doyon. Credit: Amélie Philibert, Université de Montréal
“Of all the currently known exoplanets, LHS 1140 b may be our best bet to one day indirectly confirm liquid water on the surface of an alien world beyond our Solar System,” said Cadieux, lead author of the new study. “This would be a major milestone in the search for potentially habitable exoplanets.”
Possible presence of an atmosphere and an ocean
While still only a preliminary result, the presence of a nitrogen-rich atmosphere in LHS 1140 b would suggest that the planet has retained a substantial atmosphere, creating conditions that could support liquid water. This finding favors the water world/snowball scenario as more plausible.
Current models show that if LHS 1140 b has an Earth-like atmosphere, it would be a snowball planet with a large “bull’s-eye” ocean about 4,000 kilometers in diameter, equivalent to half the surface area of the Atlantic Ocean. The surface temperature in the center of this alien ocean can be a comfortable 20 degrees centigrade.
LHS 1140 b’s likely atmosphere and favorable conditions for liquid water make it an outstanding candidate for future habitability studies. This planet offers a unique opportunity to study a world that could support life, given its position in its star’s habitable zone and the likelihood that it has an atmosphere that can retain heat and support a climate of stable.
A few years of observation ahead
Confirmation of the presence and composition of LHS 1140 b’s atmosphere and the distinction between a snow planet and a bull’s-eye ocean planet requires further observations. The research team has highlighted the need for additional measurements of the transit and eclipse with the Webb telescope, focusing on a specific signal that could detect the presence of carbon dioxide. This feature is essential for understanding atmospheric composition and detecting potential greenhouse gases that could indicate habitable conditions on exoplanets.
“Discovering an Earth-like atmosphere on a soft planet is pushing Webb’s capabilities to its limits – it’s doable; we just need a lot of observation time,” said Doyon, who is also the principal investigator of the NIRISS instrument. “The current hint of a nitrogen-rich atmosphere requires confirmation with more data. We need at least one more year of observations to confirm that LHS 1140 b has an atmosphere, and likely two or three more to detect carbon dioxide. According to Doyon, the Webb telescope will likely need to observe this system at every possible opportunity for several years to determine whether LHS 1140 b has habitable surface conditions.
Given the limited visibility of LHS 1140 b with Webb – a maximum of only eight visits per year are possible – astronomers will need several years of observations to detect carbon dioxide and confirm the presence of liquid water on the surface. the planet.
Reference: “Transmission Spectroscopy of the Habitable Zone Exoplanet LHS 1140 b with JWST/NIRISS” by Charles Cadieux, René Doyon, Ryan J. MacDonald, Martin Turbet, Étienne Artigau, Olivia Lim, Michael Radica, Thomas J. Salhi, Fauchez, Lisa Dang, Loïc Albert, Louis-Philippe Coulombe, Nicolas B. Cowan, David Lafrenière, Alexandrine L’Heureux, Caroline Piaulet, Björn Benneke, Ryan Cloutier, Benjamin Charnay, Neil J. Cook, Marylou Fournier-Tondreau, Mykhay, Valencia, accepted, The Astrophysical Journal Letters.
arXiv:2406.15136
Cadieux is a PhD student at the Université de Montréal’s Trottier Institute for Research on Exoplanets (iREx).
Other iREx researchers who contributed to this paper are René Doyon (UdeM), Étienne Artigau (UdeM), Olivia Lim (UdeM), Michael Radica (UdeM), Salma Salhi (UdeM), Lisa Dang (UdeM), Loïc Albert (UdeM ), Louis-Philippe Coulombe (UdeM), Nicolas Cowan (McGill), David Lafrenière (UdeM), Alexandrine L’Heureux (UdeM), Caroline Piaulet-Ghorayeb (UdeM), Björn Benneke (UdeM), Neil Cook (UdeM) and Marylou Fournier-Tondreau (UdeM and University of Oxford). Other contributors are based at the University of Michigan National Center of Recherche Scientifique (France), NASA Goddard Space Flight Center, American University, McGill University, McMaster University and University of Toronto. Cadieux and the UdeM team acknowledge financial support from the Canadian Space Agency for this study.