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Exoplanet LHS 1140 b may have up to 19% of its mass in water, ocean under ice, and indications of nitrogen atmosphere detected by James Webb.
According to a study published in July 2024 in the Astrophysical Journal Letters, led by Charles Cadieux from the Trottier Institute for Exoplanet Research at the University of Montreal, the planet LHS 1140 b is currently one of the most promising candidates for the presence of liquid water outside the Solar System. The James Webb Space Telescope recorded, during two transits of the planet in front of its star, indications of a nitrogen-rich atmosphere, the same gas that makes up about 78% of Earth’s atmosphere.
The detection is still considered preliminary, but it represents a significant advance in the search for potentially habitable worlds.
LHS 1140 b orbits a red dwarf 48.8 light-years away and is located in the habitable zone of the star
The star LHS 1140 is located in the constellation Cetus, approximately 48.8 light-years from Earth. It is a red dwarf with only 18% of the Sun’s mass and about 21% of its radius.
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Its luminosity is less than 0.4% of solar, which significantly reduces the intensity of emitted radiation. The star is over 5 billion years old and exhibits low stellar activity, a condition considered favorable for the preservation of planetary atmospheres.
The planet LHS 1140 b orbits this star every 24.7 days and is located within the habitable zone, a region where temperatures may allow the existence of liquid water.
Discovered in 2017 revealed a super-Earth, but new data showed a water-rich planet
The planet was discovered in April 2017 by a team led by Jason Dittmann from the Harvard-Smithsonian Center for Astrophysics, using the MEarth-South project.
Initially classified as a rocky super-Earth, the understanding of LHS 1140 b changed with new data collected in 2023. The planet has about 1.73 times the radius of Earth and approximately 5.6 times its mass, but with a density lower than expected for a predominantly rocky body.
This difference led to the conclusion that between 9% and 19% of the planet’s mass may be composed of water, a proportion hundreds of times greater than that of Earth.
Planet may be an “ocean world” with a global layer of water and permanent ice
The high fraction of water suggests that LHS 1140 b may be a so-called “ocean world,” with a deep layer of water covering much of its surface.
Models indicate that this water may be partially frozen, forming a layer of ice over a liquid ocean below. This type of structure is considered plausible on planets with high atmospheric pressure and moderate temperatures.
The presence of large amounts of water is one of the most relevant factors in the search for habitable conditions beyond Earth.
Synchronized rotation may create a permanent circular ocean on the illuminated side of the planet
Due to its proximity to its star, LHS 1140 b likely exhibits synchronized rotation, always keeping the same face turned towards the star.
This configuration creates a permanent division between the illuminated side and the dark side of the planet. Climate models suggest that the heat concentrated on the star-facing side could melt the ice in that specific region, forming a central liquid ocean surrounded by ice.
This pattern is known as a “pupil planet,” due to the appearance of a liquid circle in the center of a frozen surface.
James Webb used transmission spectroscopy to investigate the composition of the planet’s atmosphere
To investigate the presence of an atmosphere, the James Webb Telescope observed two transits of the planet in front of its star in December 2023.
The technique used was transmission spectroscopy, which analyzes the starlight filtered through the planet’s atmosphere during transit. Each gas present absorbs specific wavelengths, allowing for the identification of its composition.
The data were collected using the NIRISS instrument, specialized in near-infrared observations.
Data discard hydrogen-rich atmosphere and indicate possible presence of nitrogen
The results published in 2024 confidently ruled out the presence of a hydrogen-dominated atmosphere, a common characteristic in mini-Neptunes.
On the other hand, signals compatible with Rayleigh scattering were detected, a phenomenon associated with atmospheres composed of light molecules such as nitrogen.
The statistical confidence level was 2.3 sigma, considered a relevant indication, but still insufficient for definitive confirmation.
Nitrogen-rich atmosphere may indicate stable conditions for liquid water
Nitrogen plays a fundamental role in atmospheric stability. On Earth, it acts as a thermal regulator and maintains the pressure necessary for the existence of liquid water.
If confirmed on LHS 1140 b, it would indicate that the planet has managed to retain a secondary atmosphere, possibly formed by internal processes such as geological activity.
This would represent an unprecedented advance in the identification of atmospheres on potentially habitable planets.
Stability of the star LHS 1140 increases chances of atmosphere preservation on the planet
Unlike many young red dwarfs, LHS 1140 exhibits low stellar activity, with no significant eruptions recorded.
This stability reduces the planet’s exposure to intense radiation, a factor that often destroys atmospheres in other systems.
This characteristic makes LHS 1140 b one of the most promising candidates in the search for habitable environments outside the Solar System.
Upcoming observations from James Webb may confirm atmospheric composition and presence of additional gases
The next steps of the research involve additional observations to increase the confidence level of the data. Scientists are seeking to confirm the presence of nitrogen, as well as detect other gases such as carbon dioxide and possible indicators of atmospheric activity.
Each new observation contributes to refining the models and bringing science closer to a definitive confirmation.
The case of LHS 1140 b represents one of the most significant advances in recent astrobiology, but still without definitive confirmation.
In your view, is science close to identifying a planet with real habitability conditions, or are the challenges still greater than they seem?
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