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There are a few key features that make a planet amenable to life, at least life as earthlings know it. It should be rocky, be at the right temperature for liquid water to exist and have an atmosphere.<\/p>\n
On Thursday, a team of astronomers announced that it had identified a world with all three traits.<\/p>\n
\u201cAt this point, we have absolutely no evidence for life on the planet,\u201d said Collin Cherubim, a planetary scientist who recently earned his Ph.D. from Harvard University. \u201cBut we think all of the really important, essential ingredients are there.\u201d<\/p>\n
The rocky planet, named LHS 1140b, is a few dozen light-years from our solar system. It orbits a star within a distance known as the habitable zone, neither too hot nor too cold for liquid water to exist on the planet\u2019s surface. First discovered in 2017, the exoplanet is cooler than Earth but bigger in both size and mass.<\/p>\n
New data collected by the astronomers strongly suggests that LHS 1140b has a helium-rich atmosphere. The detection, published in the journal Science, is the first clear evidence of a potentially habitable planet with an atmosphere, and it reinforces the idea that there exists a population of worlds similar to our own with the properties necessary to sustain life.<\/p>\n<\/div>\n<\/div>\n
\u201cWhen there\u2019s one, there\u2019s more in exoplanets,\u201d said Sara Seager, an astrophysicist at M.I.T. who was not involved in the study. \u201cHopefully this is the start of something new.\u201d<\/p>\n
An atmosphere is vital for habitability because it helps a planet hold on to water, regulates the climate and protects the surface from space radiation. Scientists have found atmospheres on giant gas planets but have been uncertain whether rocky worlds, which are smaller and more difficult to detect, could retain their atmospheres, too.<\/p>\n
\u201cThis is one clear, resounding yes,\u201d said Dr. Cherubim, who spent years building a theoretical model of what the atmosphere around a rocky planet might look like. Under certain conditions, he found, lighter elements like helium would more readily escape the atmosphere. He identified LHS 1140b as a planet that could be actively losing helium to space.<\/p>\n
LHS 1140b orbits around a red dwarf, the most common type of star in our galaxy. Because red dwarfs are smaller and cooler than other types of stars, it is easier to detect rocky planets around them. But red dwarfs are also energetic, spewing violent flares of radiation that can strip away the atmospheres of nearby planets.<\/p>\n
The star hosting LHS 1140b is less active than typical red dwarfs, Dr. Cherubim said, which makes it a \u201cfront-runner\u201d for exploring habitability elsewhere in the galaxy. In 2024, he and his colleagues observed LHS 1140b passing in front of its star using a telescope at Las Campanas Observatory in Chile. Their data revealed the presence of a certain species of helium at high altitudes, indicating that the element was escaping from an otherwise difficult to detect atmosphere.<\/p>\n<\/div>\n<\/div>\n
\u201cIt\u2019s beautiful,\u201d Dr. Seager said of the detection. \u201cThere\u2019s no other explanation.\u201d<\/p>\n
In 2025, the team behind the new study observed LHS 1140b eclipsing its star yet again \u2014 but this time failed to find any sign of helium escaping from the atmosphere.<\/p>\n
\u201cThat was a big shock\u201d but \u201cnot entirely unexpected,\u201d said Shreyas Vissapragada, a planetary scientist at the Carnegie Observatories in Pasadena, Calif., and an author of the study. Scientists have observed differing amounts of helium in the atmospheres of gas giants, but this is the first time the phenomenon has been seen on a rocky exoplanet, Dr. Vissapragada said.<\/p>\n
\u201cWe\u2019re watching the atmosphere of a planet, that is in a lot of ways similar to Earth, change in real time,\u201d he said. \u201cI think that\u2019s pretty neat.\u201d<\/p>\n
Although astronomers classify the planet as Earth-like, there are key differences. LHS 1140b completes a full orbit around its star in less than 25 days. (Earth takes 365.) LHS 1140b always presents the same face to its host star, so there is no cycle of day and night. And its atmosphere is likely to be rich in helium, whereas Earth\u2019s is thick with nitrogen.<\/p>\n
Hypothetically, life could occur in such an environment. In 2020, a team of researchers led by Dr. Seager published a study indicating that yeast and E. coli could survive in an atmosphere of pure helium.<\/p>\n<\/div>\n<\/div>\n
LHS 1140b belongs to a small but tantalizing catalog of rocky worlds where scientists may someday find life. In the meantime, it can help them better understand the planet we call home.<\/p>\n
\u201cWe really want to know what planets like Earth are like, just to understand our place in the universe a bit better,\u201d Dr. Vissapragada said. Finding an atmosphere on LHS 1140b, he added, \u201cis a real stepping stone on our way to getting down to characterizing truly Earth-like exoplanets.\u201d<\/p>\n<\/div>\n<\/div>\n