Finding another planet outside of our solar system that can comfortably be called ‘Earth-like’ is one of those discoveries that — if confirmed — would be a major event. The complication here is that with every exoplanet that we discover through observations, determining the type of planet is hard enough, never mind figuring out whether it has an atmosphere, much less what’s in that atmosphere. This makes a recent report on LHS 1140 b rather exciting, as it strongly suggests that this super-Earth may have something close to an Earth-like atmosphere.

In the paper by [Collin Cherubim] and others in Science, the findings of helium occasionally escaping from its atmosphere have led to considerable excitement, as this time-variable atmospheric escape of helium suggests a helium-rich upper atmosphere that’s further depleted in hydrogen.

It should be noted, of course, that these assumptions are based on observations from roughly 49 light-years away, so there’s always some room for later adjustments. Even if confirmed, the star that LHS 1140b orbits is a red dwarf, with a nearly 25-day orbital period and light levels less than half of what Earth receives from the Sun. This would make the surface of LHS 1140b with its proposed oceans rather dim, even if it’s conceivably at temperatures well within the comfort range of us Earth-based mammals.

At 49 light-years distance, it’s also not close enough that — barring an FTL drive — we could do direct observations or visitations, but if these results hold, it’d be on the short list along with a number of other plausibly habitable exoplanets to check out once we build that first warp drive-powered starship.

Most of the gas in the Universe is a mixture of hydrogen and helium. It's thought that the initial atmospheres of most planets also start out that way. However, over billions of years, as planets evolve, the composition of their atmospheres may shift. Hydrogen can react with other chemicals, and both it and helium can be lost to space. Venus, Earth, and Mars are thought to have second atmospheres, with their original hydrogen/helium envelopes having been lost and/or transformed.

The dynamics of loss are complicated. Lighter elements are lost more easily, but hydrogen can be protected by being incorporated into molecules like methane and ammonia. The gravity of the body can help retain some molecules, and a magnetic field can limit radiation's ability to blast material out of the atmosphere. Proximity to a star will matter too, both because of the radiation it produces and because it can heat the atmosphere and expand it to where gravity's influence is less substantial.

Given all these complications, it can be difficult to know what to expect to find on exoplanets. But a study in Wednesday's issue of Nature describes observations of helium being lost from the atmosphere of an exoplanet orbiting the star LHS 1140, about 50 light-years away. Based on the rate at which the helium is being lost, we can infer something about the remaining atmosphere.

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WD 1856 b is the only confirmed case of a planet that survived the death of a Sun-like star. It’s a Jupiter-size world orbiting a white dwarf—the burned-out remnant of a Sun-like star. Now, a team of astronomers has used the James Webb Space Telescope to take a closer look at this planet for the first time, and what they found makes an already strange system even stranger.

A feeding frenzy

WD 1856 b was an accidental discovery. Astronomers pointed the TESS observatory at a sample of roughly 2,000 white dwarfs in 2020. These stars are the remains of a Sun-like star that have already gone through a red-giant phase, leaving behind an Earth-size body that’s primarily composed of elements like carbon and oxygen. The TESS team was searching for small objects like comets or asteroids that might transit across the face of these dead stars.

What they found in the WD 1856 system was a gas giant. “As soon as they looked at it, they said, okay, that’s weird,” said Christopher O’Connor, a theoretical astrophysicist at Cornell University and co-author of the recent Nature study on WD 1856 b.

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