For the first time in history, astronomers have confirmed an atmosphere surrounding a rocky, Earth-like planet located within its star's habitable zone. The subject is LHS 1140 b, a world with a mass approximately 5.6 times that of Earth orbiting just 48 light-years away. This discovery is not merely a numerical milestone; it provides tangible proof that terrestrial planets can retain gaseous envelopes for billions of years, a fundamental prerequisite in the search for extraterrestrial life.

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The Helium Trick and Stellar Transit

The detection method relies on a subtle physical phenomenon: as the planet transits in front of its star, a sliver of starlight filters through the planetary atmosphere. The research team identified a small dip in light intensity at a specific infrared wavelength, corresponding exactly to the spectral signature of helium. The presence of this light gas "escaping" into space is a key indicator of a denser, more complex atmosphere. While it remains unknown whether the air contains oxygen, carbon dioxide, or water vapor, confirming the atmospheric structure radically changes the planet's habitability status.

Une atmosphère détectée sur LHS 1140 b relance totalement l'espoir de ... — https://amphisciences.ouest-france.fr/2025/12/une-atmosphere-detectee-sur-lhs-1140-b-relance-totalement-lespoir-de-trouver-de-la-vie-ailleurs/

Challenging Atmospheric Loss Models

This discovery arrives at a critical moment for the scientific community, which has long debated whether red dwarfs—small, cool stars like LHS 1140 b's host—can host habitable worlds. These stars emit high-energy radiation that, according to previous models, should have stripped away the atmospheres of nearby planets over time. The fact that LHS 1140 b has survived, while its smaller, less gravitationally bound neighbor (LHS 1140 c) appears to have lost its atmosphere, suggests that planets may retain their atmospheres much longer than previously assumed. This result indirectly validates predictive models like the STEHM software, which aims to optimize the search for planets with stable atmospheres.

LHS 1140b - A Habitable Super-Earth 39 Light Years Away? - YouTube — https://www.youtube.com/watch?v=4PVGe2GNbYc

Toward Chemical Composition Analysis

The estimated surface temperature of LHS 1140 b, prior to the atmospheric discovery, was around -53 degrees Fahrenheit (approx. -47 °C), a cold value but potentially compatible with liquid water due to the greenhouse effect. The next step for astronomers will be to determine the full composition of the atmosphere and check for oceans. As Robin Wordsworth, a professor at Harvard and dissertation advisor to lead authors, noted: "Twenty years ago we wondered if other terrestrial planets even existed. Now we know at least one has kept its atmosphere."