In an exciting breakthrough, a McMaster researcher is part of an international team that has discovered a potentially habitable icy exoplanet beyond our solar system. Named LHS 1140 b, this exoplanet is located about 48 light-years away in the constellation Cetus. It orbits a low-mass red dwarf star that is roughly one-fifth the size of the Sun, making it one of the closest exoplanets to our solar system within its star’s habitable zone.
Exoplanets found in this “Goldilocks Zone” have temperatures that could allow water to exist in liquid form, which is crucial for life. “We had enough information about the mass and orbit of LHS 1140 b to successfully make the case to go and check whether it has an atmosphere and may be a prospective place for life elsewhere in the universe,” says Ryan Cloutier, an assistant professor in the Department of Physics and Astronomy, who contributed to the study led by researchers at l’Université de Montréal.
Since its discovery in 2017, scientists have been keen to find out whether LHS 1140 b is a mini-Neptune—a small gas giant with a thick hydrogen-rich atmosphere—or a rocky planet larger than Earth, known as a super-Earth. To distinguish between these two possibilities, they needed a detailed characterization of the planet’s atmosphere using the James Webb Space Telescope, which Cloutier calls “the most powerful telescope that humankind has ever built.”
The team was awarded time with Webb last December. Their observations were carried out using the Canadian-built Near-Infrared Imager and Slitless Spectrograph (NIRISS) instrument. The data collected helped rule out the mini-Neptune scenario and provided tantalizing evidence suggesting LHS 1140 b is an icy super-Earth that may even have a nitrogen-rich atmosphere similar to our own.
The findings, combined with measurements of the exoplanet’s mass and size, reveal that LHS 1140 b is less dense than expected for a rocky planet with an Earth-like composition. This suggests that 10 to 20 percent of its mass may be composed of water. This points to LHS 1140 b being a compelling candidate for a water world, likely resembling a snowball or ice planet with a potential liquid ocean at the sub-stellar point—the area of the planet’s surface that always faces its star, similar to how the Moon is locked in orbit around Earth.
“The question of ‘are we alone in the universe’ has been asked for millennia. It’s only in the last three years since the launch of the James Webb Space Telescope that we’ve been able to go and search for signatures of Earth-like planets and confirm whether they’re conducive to hosting life,” explains Cloutier. “It’s difficult and it requires a lot of time, but it would be so impactful if it was successful. We’re seeing hints of that success here for the very first time. Getting confirmation would be so revolutionary—not just for the field of exoplanetary astronomy but for scientific exploration.”
More observations with Webb are needed to confirm the presence and composition of LHS 1140 b’s atmosphere and to determine whether it’s a snowball planet or a bull’s-eye ocean planet. The team hopes to focus on a specific signal that could unveil the presence of carbon dioxide, which is crucial for understanding the atmospheric composition and detecting potential greenhouse gases that could indicate habitable conditions on this exoplanet.
Due to limited visibility with Webb, astronomers will need to observe this system at every possible opportunity for several years to determine whether LHS 1140 b has habitable surface conditions. This planet provides a unique opportunity to study a world that could support life, given its position in the habitable zone and the likelihood of having an atmosphere that can retain heat and support a stable climate.
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