Has a rocky planet really managed to keep its air for three billion years, at just 48 light-years from us? That is the question stirring the exoplanetology community since the Science publication of July 16, 2026, by a Harvard team. The researchers report that the relatively nearby super-Earth LHS 1140b appears to be leaking helium into space, which would imply that it still possesses a substantial atmosphere billions of years after its formation. A result that, if confirmed, would rewrite the rules about how rocky worlds can retain a gaseous envelope in the face of their star’s fury.
Key takeaways
- Has a rocky planet’s atmosphere truly endured three billion years at only 48 light-years away?
- A helium signal detected in 2024 vanished completely in 2025: cosmic phenomenon or simple instrumental artefact?
- The deep layers of LHS 1140 b remain unexplored — the real mystery may lie beneath.
An unlikely bet that paid off
The story begins with a calculation, not an observation. Before aiming a telescope at LHS 1140 b, Collin Cherubim did the math, and the model he constructed with his collaborators predicted that this rocky planet, 48 light-years away, would host a helium-rich upper atmosphere slowly escaping into space. A prediction deemed a bit wild, since no one had ever applied this technique to a rocky world. The detection of helium escape by near-infrared spectroscopy had previously been used only on gaseous giant exoplanets, and applying it to a rocky planet required both a precise theoretical target and an instrument capable of resolving a faint signal.
Even within the team, belief wasn’t wholehearted. David Charbonneau, Cherubim’s thesis co-advisor and head of the Harvard astronomy department, initially expressed skepticism about this plan born of a purely mathematical calculation never tested on a rocky world, but the results convinced him. To test the hypothesis, the team used an instrument just installed in Chile, on the Magellan telescopes. The 6.5-meter Magellan telescope, which had just received a new high-resolution spectrograph sensitive to this helium line in the near infrared, proved perfectly suited to the task. In 2024, on a night when two planets in the system transited the star, the signal appeared clearly on one and was absent on the other. During the transit of the larger planet, researchers observed a dip in the stellar brightness at a wavelength characteristic of helium absorption, whereas the passage of the smaller planet showed no such signal.
This contrast changes everything in the interpretation of the signal. Without it, one might suspect an instrumental artefact or contamination tied to the star itself, a capricious red dwarf. With it, the evidence gains credibility: two worlds in the same system, exposed to the same radiation, but only one shows the signal. It is precisely this kind of check that tipped Charbonneau’s initial skepticism.
Three billion years of resistance… or almost
The number that captures the imagination is the proposed longevity of this atmosphere. According to the researchers’ estimates, LHS 1140 b’s helium envelope would have endured for more than three billion years. The planet has traversed, without losing its atmosphere entirely, most of the host star’s lifetime, since LHS 1140 is an inactive M-dwarf about 3 billion years old. An achievement given that red dwarfs are known to bombard their planets with X-rays and extreme ultraviolet radiation, a mechanism that, in theory, should erode any light atmosphere rapidly.
But the story does not end with a simple confirmation. It features an unexpected twist. The team determined that helium was escaping from LHS 1140 b’s atmosphere in 2024 due to heating by the star’s X-ray and extreme ultraviolet radiation, but 2025 observations revealed no helium escape, suggesting that atmospheric loss is variable. A variability that excited the researchers more than unsettled them: they see in it the proof of a dynamic phenomenon observable on human timescales. It’s even notable to mention: watching the atmosphere of a world tens of billions of kilometers away evolve within a single year is a bit like watching a sand dune move in real time.
Why some astronomers remain cautious
The scientific community, for its part, tempers the media enthusiasm. Asked by Science itself, astronomer René Doyon of the University of Montréal, not involved in the study, aptly sums up the mixed sentiment: “It’s an extraordinary result if confirmed,” he says, adding that “the signal is definitely there.” The conditional isn’t trivial. A statistically robust signal is not yet definitive proof of a complete atmospheric composition.
In Nature, other voices urge methodological caution. Vatsal Panwar, an astronomer at the University of Birmingham, suggests that more measurements are needed to rule out spectroscopic observing errors, especially those caused by the host star itself. A view echoed implicitly by the study’s authors: the researchers themselves acknowledge that detections followed by non-detections are relatively common when observing helium, Cherubim noting that they seem to be the rule rather than the exception. The disappearance of the signal in 2025 may not be a cosmic mystery, but a behavior already documented elsewhere in the universe. Still, for now, this helium escape from LHS 1140 b remains a single data point.
We should also remember what this discovery does not say. It does not reveal life, vegetation, oceans, or civilization, but it does establish that LHS 1140 b has retained a gaseous envelope despite billions of years of exposure to its star’s radiation. And above all, the detected helium belongs to the upper, thinnest layer of the atmosphere. The published study describes a high atmosphere dominated by helium and depleted in hydrogen, with heavier volatile gases potentially remaining trapped closer to the planet, below the altitude reached by the helium escaping. What lies beneath—potentially water, carbon dioxide, or nitrogen—remains entirely invisible to current instruments.
The logical next chapter of the story is already playing out with the James Webb Space Telescope, the only instrument capable of probing these deeper layers and richer sources of information about any real habitability. LHS 1140 b is also among the top targets of the rocky worlds program, a sign that the community, despite its reservations, does not intend to let this lead slip away. The debate is therefore not settled between a historic discovery and a fragile signal: it continues, one observation at a time, on a planet that has already surprised everyone twice in two years.
Sources: sciencesetcivilisations.fr | cite-espace.com
