The mild exoplanet LHS 1140 b may be a world completely covered in ice (left) similar to Jupiter’s moon Europa, or it may be an icy world with a liquid substellar ocean and cloudy atmosphere (center). LHS 1140 b is 1.7 times the size of our planet Earth (right) and is the most promising exoplanet in the habitable zone yet found in the search for liquid water outside the Solar System. Credit: Benoit Gougeon, Université de Montréal
A team of astronomers has made an exciting discovery about the temperate zone exoplanet LHS 1140 b: could be a promising ‘super-earth’ covered in ice or water.
LHS 1140 b, once considered a mini-Neptuneis now considered a possible super-Earth with a nitrogen-rich atmosphere, he suggests The James Webb Space Telescope data. It is located in the habitable zone and 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 essentially be a gaseous planet, but very small compared to Neptune. 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 came 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, which may harbor an atmosphere and even an ocean of liquid water. The results of this discovery by astronomers from the Université de Montréal are available on ArXiv and will soon be published in The Astrophysical Journal Letters.
As the most advanced space telescope to date, the James Webb Space Telescope excels in the study of exoplanets. Its cutting-edge technology allows astronomers to probe the atmospheres of distant worlds, analyze their composition and assess their potential to support life. Credit: Northrup Grumman
Exoplanet in the “Goldilocks” Zone
LHS 1140 b, an exoplanet orbiting a low-mass red dwarf roughly one-fifth the size of the Sun, has captivated scientists as one of the closest exoplanets to our Solar System that lies in its star’s habitable zone. Exoplanets found in this “Goldilocks Zone” have temperatures that would allow liquid water to exist on them – liquid water is a key element for life as we know it on Earth.
Earlier this year, researchers led by Charles Cadieux, Ph.D. student at the Trottier Institute for Exoplanet Research (iREx) at UdeM, led by Professor René Doyon, reported new mass and radius estimates for LHS 1140 bs with exceptional accuracycomparable to those of the 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 lead author of the paper. Credit: Courtesy
One of the critical questions about LHS 1140 b has been whether it is a mini-Neptune exoplanet (a small gas giant with a dense hydrogen-rich atmosphere) or a super-Earth (a rocky planet larger than Earth). This second scenario included the possibility of a so-called “Hyckesian world” with a global liquid ocean enveloped by a hydrogen-rich atmosphere that would exhibit a distinct atmospheric signal that could be observed with the powerful Webb Telescope.
New insights from Webb Data
Through an extremely competitive process, a team of Webb astronomers was awarded valuable “Director’s Discretionary Time” (DDT) last December during which two transits of LHS 1140b were observed by Canada’s Near-Infrared Imager and Slitless Spectrograph (NIRISS). tool. This DDT program is only the second dedicated to the study of exoplanets in Webb’s nearly two years of operation, underscoring the importance and potential impact of these findings.
Analysis of these observations strongly ruled out a mini-Neptune scenario, with exciting evidence suggesting that exoplanet LHS 1140b is a super-Earth that may even have a nitrogen-rich atmosphere. If this result is confirmed, LHS 1140 b would be the first temperate planet to show evidence of a secondary atmosphere that formed after the planet’s initial formation.
Estimates based on all the accumulated data show that LHS 1140b is less dense than expected for a rocky planet with a similar composition to Earth, suggesting that 10 to 20 percent of its mass may be water. This discovery indicates that LHS 1140b is an impressive water world, likely resembling a snowball or ice planet with a potential liquid ocean at the substellar point, an area of the planet’s surface that would always face the system’s host star due to the planet’s expected synchronous rotation (similar to Earth’s Moon).
René Doyon. Credit: Amélie Philibert, Université de Montreal
“Of all the currently known temperate exoplanets, LHS 1140 b could be our best bet to one day indirectly confirm liquid water on the surface of an alien world outside our solar system,” said Cadieux, lead author of the new study. “This would be a significant milestone in the search for potentially habitable exoplanets.”
Possible presence of atmosphere and ocean
Although still only a preliminary result, the presence of a nitrogen-rich atmosphere on LHS 1140 b would indicate that the planet has retained a substantial atmosphere, creating conditions that could support liquid water. This discovery favors the water world/snow globe scenario as the most likely.
Current models suggest that if LHS 1140 b has an Earth-like atmosphere, it would be a snowball with a huge “bull’s-eye” ocean about 4,000 kilometers in diameter, equivalent to half the surface area of the Atlantic Ocean. The surface temperature at the center of this alien ocean could even be a comfortable 20 degrees Celsius.
LHS 1140 ba’s potential atmosphere and favorable conditions for liquid water make it an exceptional candidate for future habitability studies. This planet provides a unique opportunity to study a world that could support life, given its location in its star’s habitable zone and the likelihood that it has an atmosphere that can retain heat and support a stable climate.
Several years of observation ahead
Confirming the presence and composition of LHS 1140’s atmosphere and distinguishing between the snowball planet and bull’s-eye ocean planet scenarios requires further observations. The research team highlighted the need for additional measurements of the transition and eclipse using the Webb Telescope, focusing on a specific signal that could reveal the presence of carbon dioxide. This property is crucial for understanding the composition of the atmosphere and detecting potential greenhouse gases that could indicate habitable conditions on an exoplanet.
“Detecting an Earth-like atmosphere on a temperate planet pushes Webb’s capabilities to its limits – it’s doable; we just need a lot of time to observe,” said Doyon, who is also principal investigator of the NIRISS instrument. “The current indication of a nitrogen-rich atmosphere requires further data confirmation. We need at least one more year of observations to confirm that LHS 1140 b has an atmosphere, and probably 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.
Due to the limited visibility of LHS 1140 bs by 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 planet’s surface.
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. Fauchez, Salma Salhi, 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, Mykhaylona Plokov, Mykhaylona Valencia area, received, The Astrophysical Journal Letters.
arXiv:2406.15136
Cadieux is a PhD student at the Trottier Institute for Exoplanet Research (iREx) at the Université de Montréal.
Other iREx researchers who contributed to this article 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 a University of Oxford). Other contributors are from the University of Michigan, USA Center national de recherche scientifique (France), NASA Goddard Space Flight Center, American University, McGill University, McMaster University and University of Toronto. Cadieux and the UdeM team acknowledge the financial support from the Canadian Space Agency for this study.