Astronomers believe the exoplanet may have had ample opportunity for life to emerge
Scientists have made a major breakthrough in the hunt of life outside our solar system after spotting an "Earth-like" planet.
LHS 1140 b, located just 49 lightyears from our planet, is roughly six times Earth's mass but is 1.7 times larger.
The exoplanet occupies what astronomers call the Goldilocks zone, positioned at precisely the right distance from its star where temperatures let liquid water exist.
Although researchers have identified dozens of rocky worlds in similar orbital positions, this is the first time one has demonstrated evidence of atmospheric gases.
"An atmosphere is essential for a planet to support life as we know it," said Dr Collin Cherubim of Harvard University, the lead author of the new research.
"This is the first time anyone has found an atmosphere on a rocky planet in the habitable zone of another star."
Atmospheres serve multiple vital functions, including shielding surfaces from harmful cosmic radiation, enabling photosynthesis and respiration, regulating temperatures, and permitting water to remain in liquid form.
The research team identified the breakthrough whilst observing helium escaping from the planet using the Magellan Clay telescope at Chile's Las Campanas Observatory.
Scientists estimate LHS 1140 b to be around five billion years old, meaning its helium reserves should have depleted entirely without some mechanism to maintain them.
The detection of escaping helium indicates the presence of an atmosphere that slows the rate at which gas disperses into space.
Notably, another planet within the same stellar system displays no signs of either helium or atmospheric gases.
"Twenty years ago, we wondered whether other terrestrial-type planets even existed," said Robin Wordsworth, professor of environmental science and engineering, and professor of Earth and planetary sciences, at Harvard.
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"Then we learned they're common, and found some in the habitable zone. The next question was whether any of them had managed to keep an atmosphere. Now we know at least one has."
Astronomers believe the planet's atmosphere has likely persisted for over three billion years, providing ample opportunity for life to emerge.
The building blocks of life may have arrived via comets and meteors, mirroring the process thought to have seeded Earth billions of years ago.
Given that LHS 1140 b orbits a red dwarf star, scientists anticipate surface temperatures comparable to those on Earth.
Dr Jo Barstow, an exoplanet atmosphere specialist from the Open University, offered a measured assessment of the findings.
"This discovery of escaping helium on a rocky world is a really important milestone," she said.
"It doesn't mean that it is necessarily habitable, and the same X-ray and ultraviolet radiation driving the helium escape may make conditions on the surface inhospitable."
She added that the discovery confirms rocky planets orbiting red dwarfs can maintain atmospheres, though determining the atmosphere's composition requires further observation.
The Harvard researchers now plan to analyse the atmospheric makeup and investigate whether surface oceans exist.
LHS 1140 b, first identified in 2017, has been designated a priority target for the Rocky Worlds programme, which employs both the James Webb Space Telescope and Hubble Space Telescope to search for exoplanet atmospheres.
Dr Jason Dittmann, assistant professor of astronomy at the University of Florida and study co-author, said: "JWST data over the next four to five years will look for water, and if there's water in the atmosphere, then it's probably a stable atmosphere that will persist."
