Evidence of an atmosphere detected for the first time on a rocky terrestrial exoplanet
Scientists have now detected the first evidence of an atmosphere on a rocky terrestrial exoplanet that is also located in the habitable zone. The exoplanet, dubbed LHS 1140 b, is located circling a red dwarf star about 48 light years away and is estimated to have about 5.6 times the mass of Earth and about 2.4 times the diameter.
To test their prediction, the team used the Warm Infrared Echelle (WINERED) Spectrograph on the Magellan Telescope at Las Campanas Observatory in Chile. They observed a rare alignment, where LHS 1140 b and another planet [in the system] transited their star on the same night.
Although one planet showed no evidence of an atmosphere, the other, LHS 1140 b, showed helium escaping from around it, confirming that it retains an atmosphere.
You can read their paper here [pdf]. The discovery is of significance, as it proves finally — more than two decades after the first detection of an exoplanet — that rocky exoplanets outside our solar system can have an atmosphere. There is also evidence that this loss of helium might be seasonal in nature. From their abstract:
Helium absorption is detected in 2024 but not in 2025, indicating time-variable atmospheric escape. We interpret these results as indicating an upper atmosphere dominated by helium and depleted in hydrogen, with other volatile species trapped at lower altitudes, consistent with atmospheric fractionation models. No helium absorption is detected for LHS 1140c, a smaller and more strongly irradiated
exoplanet in the same system.
The planet has an orbit 24.7 days, and is located in the habitable zone, though overall it gets only 42% of the radiation from its star compared to Earth. Thus, it is very cold on this planet, with a gravity significant heavier than Earth’s. In other words, even if it has an atmosphere, it remains a very alien place.
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The linked article/press release from the Harvard & Smithsonian Center for Astrophysics mentions that research into the structure and composition of the lower portions of LHS 1140 b’s atmosphere will be on-going. One research goal is to determine, if possible, whether the surface of the planet can support liquid water, either sporadically or continuously.
If the surface-adjacent atmosphere turns out to have a partial pressure of oxygen compatible with human respiration, and there are no harmful atmospheric compounds present – e.g., excessive CO2 or sulphuric gases – that could make LHS 1140 b a potentially interesting bit of real estate for us in centuries to come even if it’s otherwise an iceball. Humanity, a few centuries hence, should be perfectly capable of the sort of mega-engineering needed to terraform a planet by warming it up.
Doing a bit of searching, I find that the surface gravity of LHS 1140 b is only about 10% higher than Earth’s, a figure that ought to be well within human tolerance.
Starfleet will need to mark this one as well worth a closer look.
While looking this up, I thought that the gravity would be much higher. Grok thought the gravity would be about 3% lighter.
Why it’s lower than you expected:You have 5.6× more mass, which pulls harder.
But the surface is 2.4× farther from the center.
Gravity follows an inverse square law, so the extra distance hurts you a lot: the 2.4× radius gives you a 5.76× bigger denominator.
5.6 / 5.76 ≈ 0.97 → slightly weaker gravity than Earth.
Slightly less is even better than slightly more. It seems Grok is smarter than my usual search engine.
Gravity increases with the mass, which increases with the cube of the diameter (radius). Gravity decreases with the square of the distance (radius). The result is that for a uniformly dense spherical object, gravity increases linearly with diameter.
From this we can conclude that this planet is less dense than Earth.
Or we can do the math:
2.4 times the diameter is 13.8 times the volume
5.6 times the mass divided by 13.8 times the volume results in 0.41 times the density.
That’s the density up to the visible horizon. Like, Neptune is probably mostly molten rock. But its atmo blocks and reflects light, and it’s the atmo that we get to see from outside.
To clarify, this is not the first detection of atmo on any superEarth up to 5.6 mass (M⊕). GJ 9827 d is a 3.42 M⊕ and has an atmosphere, for one.
This might be the first detection of atmo on this particular world.
As Robert’s post noted, it’s the first super-Earth exo-planet with an atmosphere that is also in its star’s habitable zone.