A rocky planet about 40 light-years from Earth may have something scientists have struggled to come up with on similar worlds – a lasting atmosphere.
The planet, called LHS 1140b, was first discovered in 2016. Now, new research published in Science shows that it can still hold onto an atmosphere — despite billions of years of exposure to its host star.
The discovery is remarkable because most rocky planets found around small, cool stars appear to have lost their atmospheres over time. If LHS 1140b does indeed have one, it could become an important target in the search for potentially habitable worlds beyond our Solar System.
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Discovered with the help of artificial intelligence
LHS 1140b was discovered by astronomer Jason Dittmann of the University of Florida while searching for planets that pass in front of their stars and briefly dim them. Detecting these small changes from Earth is difficult because clouds, humidity and other weather conditions can interfere with observations.
To improve the search, Dittmann trained a machine learning program to distinguish between signals caused by Earth’s atmosphere and those produced by an orbiting planet. This approach led to the discovery of LHS 1140b.
The planet is made up of rock, not gas, and orbits within the habitable zone of its small, cool star — where temperatures can allow for liquid water under the right conditions. Another planet, LHS 1140c, also orbits the same star, but is outside the habitable zone.
Helium leak reveals atmosphere
The new study focused on a surprising discovery. Using the Magellan Clay telescope in Chile, scientists discovered helium escaping from LHS 1140b. Helium can leak out of a planet’s atmosphere, and this also happens on Earth.
But LHS 1140b is an old planet. Scientists therefore expected that all helium would have disappeared into space a long time ago. The fact that helium is still being discovered suggests that the planet is somehow replacing it — pointing to the existence of an atmosphere.
Previous sightings also helped solve the mystery. Shortly after the planet was discovered, Dittmann obtained X-ray observations of the star. These measurements showed how much high-energy radiation is reaching the planet, and allowed the researchers to calculate how quickly helium should disappear.
The calculations showed that without a continuous source of helium, nothing would be left today. This means that the planet needs to replenish its supply regularly.
Two possible explanations
However, the researchers cannot yet say with certainty whether LHS 1140b has a stable atmosphere. One possibility is that the planet is mostly bare rock that occasionally releases gas from its interior. Another possibility is that it has a long-lasting atmosphere that slowly leaks helium into space – much like the Earth does.
James Webb will search for traces of life
The next step is to look for other gases. LHS 1140b has been selected for the Rocky Worlds Director’s Discretionary Time Program — a joint project that uses the James Webb Space Telescope and the Hubble Space Telescope to study rocky planets around dwarf stars.
Over the next four to five years, Webb will search for gases such as water vapor and carbon dioxide. Finding these molecules will provide far stronger evidence that the planet has a stable atmosphere.
A breakthrough in the search for life
If future observations confirm that LHS 1140b has a long-lasting atmosphere, it will mark one of the first known Earth-sized rocky planets around a small star to have retained one.
That would make it one of the most promising nearby worlds for scientists trying to understand which planets outside our solar system might one day prove capable of sustaining life.
