A Landmark Discovery in Deep Space
For the first time, astronomers have confirmed the presence of an atmosphere on a rocky planet located in the habitable zone of its star—a region where conditions might be right for liquid water. The planet, known as LHS 1140 b, has become a prime subject
of interest not just because it has an atmosphere, but because that atmosphere appears to be actively changing. Researchers observed a significant amount of helium escaping the planet during observations in 2024, but when they looked again in 2025, the signal had vanished. This variability is the crucial clue, suggesting dynamic processes are at play and offering an unprecedented real-time glimpse into planetary evolution.
Meet Planet LHS 1140 b
Located approximately 49 light-years from Earth in the constellation Cetus, LHS 1140 b is what astronomers call a 'super-Earth'. It is about 5.6 times the mass of our own planet and roughly 1.7 times its radius. While larger and more massive than Earth, its composition is believed to be rocky. It orbits a small, cool star known as a red dwarf. Because it resides in the star’s habitable zone, it receives enough energy for its surface temperature to potentially allow for liquid water, a key ingredient for life as we know it. Before this discovery, whether a planet like this could hold onto an atmosphere over billions of years was a major unanswered question in astronomy.
The Cosmic Detective Work
Detecting an atmosphere 49 light-years away is an immense technical challenge. The team of scientists accomplished this using a method called transit spectroscopy. As LHS 1140 b passed in front of its host star from our point of view, astronomers at the Magellan Clay telescope in Chile analysed the starlight that filtered through the very edge of the planet. The planet's atmosphere absorbs certain colours, or wavelengths, of this light. Each chemical element leaves a unique fingerprint. In this case, the spectrograph—an instrument that splits light into its component colours—revealed the distinct signature of helium. This confirmed not only that an atmosphere was present but also allowed scientists to study its outermost layers.
Why the Vanishing Helium Is So Important
The most compelling part of the discovery is that the helium signal was not constant. It was strong in 2024 but absent in 2025. This time-variable escape suggests the atmosphere is not static but is being actively stripped away, likely by high-energy radiation like X-rays from its parent red dwarf star. Red dwarfs are known for their intense stellar activity, which can be harsh for nearby planets. Seeing the atmospheric escape change over just one year provides a direct look at this process in action. It transforms the planet from a static object into a dynamic world with a story to tell about its survival. This variability helps scientists understand whether the planet is simply 'burping' gas occasionally or if it has a stable, long-term atmosphere that is slowly leaking, much like Earth does.
A Window into Planetary Lives
Helium is the second-most abundant element in the universe, and because it is so light, it easily escapes a planet's gravitational pull. This makes it an excellent tracer for atmospheric loss. The finding supports theories that many rocky planets may begin their lives as larger worlds with thick hydrogen and helium envelopes, which are gradually stripped away by their stars. Detecting this helium-rich phase gives astronomers a vital snapshot of a planet in transition. It helps bridge the gap between large, gassy 'mini-Neptunes' and smaller, rocky terrestrial worlds like Earth. This discovery proves that we now have the capability to not just find these worlds but to begin understanding their climates and their ability to hold onto the very air that could make them habitable.
