Astronomers have made a groundbreaking discovery in the search for life beyond our solar system: the first confirmed atmosphere on a rocky exoplanet within its habitable zone. LHS 1140b, a planet 49 light-years from Earth, orbits a small red dwarf star and presents a prime candidate for supporting liquid water.
The detection marks a significant milestone, as atmospheres have previously only been identified on gas giants and 'sub-Neptunes', or as signs of atmospheres on rocky exoplanets outside habitable zones. Dr Collin Cherubim, lead author and formerly of Harvard University, highlighted the importance of this finding: 'This is the first direct identification of an atmospheric species for any rocky exoplanet, regardless of its location relative to the habitable zone.'
LHS 1140b was discovered in 2017 and boasts a mass 5.6 times that of Earth and a radius 70% larger. Despite these differences, Dr Cherubim noted similarities in overall composition and temperature. Crucially, the presence of an atmosphere could prevent water from escaping and shield the planet from radiation. Observations using an infrared spectrograph on the Magellan Clay telescope in Chile revealed helium escaping from the planet, a key indicator of an atmosphere. However, subsequent observations did not detect helium, prompting extensive re-analysis to rule out false positives.
The exoplanet orbits a small red dwarf star in the constellation of Cetus, which emits a higher proportion of ionising radiation than our Sun. Nevertheless, its low flare activity is beneficial for maintaining an atmosphere. Researchers did not find an atmosphere around LHS 1140c, another rocky planet orbiting the same star, underscoring the unique nature of LHS 1140b.
Professor Jayne Birkby, an astrophysics expert at the University of Oxford, praised the discovery as 'fantastic'. She noted that while red dwarf planets offer the best chance for studying nearby rocky exoplanets in habitable zones, their host stars are often active and strip away planetary atmospheres. The detection of an atmosphere around LHS 1140b is a vital step in understanding the conditions for life around such stars.