First Evidence Of Atmosphere On Potentially Life-Friendly Planet Found

Astronomers Found a Planet’s Atmosphere Escaping, Then It Disappeared

A rocky planet sitting in a potentially life-friendly orbit has an atmosphere, and astronomers have confirmed it for the first time.

LHS 1140b orbits a dim red star about 48 light-years from Earth, close enough to study in detail. It sits in the zone around its star where liquid water could, in theory, exist on its surface, making it one of the more promising nearby candidates for conditions that might support life. Until now, data confirming atmospheres on rocky exoplanets has been extremely limited. A new study published in the journal Science changes that. Shreyas Vissapragada, a researcher on the team, called it “clear evidence of an atmosphere” on a planet like this.

There’s a twist. When the team looked again a year later, the signal was gone.

That doesn’t undercut the discovery. It raises a different, pointed question: can a planet hold onto the air it needs for life while radiation from its star drives some of that atmosphere into space?

A 6.5-Hour Watch Caught Helium Streaming Off the Planet

Researchers used an instrument called WINERED, mounted on the Magellan Clay telescope at Las Campanas Observatory in Chile. Over 6.5 hours in September 2024, they watched two planets in the system cross their shared star, separated by just 39 minutes, collecting 70 measurements: 35 between crossings, 12 during the crossing of a smaller planet called LHS 1140c, and 23 during the crossing of LHS 1140b. Comparing the light from each crossing to the baseline starlight let them search for chemical signatures left by any atmosphere.

For LHS 1140b, the signal was clear. A pattern of light absorption, consistent with helium being pushed out by the star’s radiation, appeared during the crossing and lingered slightly before and after, suggesting helium streaming ahead of the planet in its orbit, a behavior seen before around gas giants but never around a small rocky world that could support life.

Signals from water or carbon dioxide, the gases usually found lower in a planet’s atmosphere, are especially faint and hard to catch, even for powerful telescopes like the James Webb Space Telescope. So the team went looking for helium instead, since it tends to show up more clearly higher up.

The Upper Atmosphere Is Mostly Helium, Not Hydrogen

What the team found wasn’t just escaping gas but a specific kind of it. The upper atmosphere of LHS 1140b is dominated by helium, with hydrogen present in low abundance, a departure from expectation since many models suggest planets like this begin hydrogen-rich. A long-term sorting process appears to explain this: over billions of years, the star’s radiation appears to have driven off lighter hydrogen while heavier gases, including helium, remain in larger concentrations. The escape is too weak to carry off heavier elements like oxygen, carbon, or nitrogen, so those gases likely get left behind and build up deeper in the atmosphere over time.

LHS 1140, the host star, is an old, quiet red dwarf. Its low brightness and small size make it ideal for this kind of study, since even a thin atmosphere can leave a measurable mark on the star’s dim light.

The Signal Disappeared a Year Later

One of the most puzzling parts of the discovery came the following year. Observing LHS 1140b again in 2025, the team found the helium signal gone, even after the data were independently re-reduced using a different code.

Researchers don’t think the atmosphere vanished. They suggest the escape may be variable, ebbing and flowing with the star’s radiation output, similar to how the Sun’s activity rises and falls over its 11-year cycle. If the star’s radiation dropped low enough between observations, the signal could fall below what the 2025 instruments could detect. The team cannot rule that out.

A different story plays out with the sibling planet in the system, LHS 1140c. It orbits much closer to the star and receives roughly five times the radiation Earth gets from the Sun. No helium escape was detected from it, consistent with earlier observations suggesting this inner planet has little to no atmosphere left. The two planets sit on opposite sides of what astronomers call the cosmic shoreline, a proposed boundary separating planets that hold onto atmospheres for billions of years from those that don’t. Researchers note this is a fit with the theory, not proof of it.

Water on LHS 1140b Could Still Survive the Escape

If LHS 1140b holds significant water, that water could survive the escape by condensing and freezing in the upper atmosphere before it ever reaches altitudes where it could be lost to space. The planet’s cool temperatures make this plausible. This finding doesn’t rule out that possibility, or the alternative some researchers have proposed: that the planet’s mass, about 5.6 times Earth’s, and its size, about 1.73 times Earth’s radius, simply reflect an Earth-like rocky composition topped with an atmosphere.

Having an atmosphere is not the same as keeping one. Whether LHS 1140b holds onto enough air to remain a candidate for life is now a measurable question, and scientists are watching for the answer.

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