Three summers ago I got moderately excited about Gliese 3053 = LHS 1140 b - the M star's outer planet, 24.7 days. I didn't really look at later-discovered c, which I thought would be irradiated and airless. The AlfvƩn surface habitability criterion looked good for b however so it got attention at the time.
I started pondering underground water as might deflate the rocky part's density and raise its radius, so held off on saying much more about this unconstrained planet. I had questions needing answers about its atmospheric composition.
So: more data's come in (h/t Zim, but poorly worded). Still looking at a mass of 5.60 ±0.19 Earth masses (M⊕) and a radius of 1.730 ±0.025 Earth radii (R⊕)
. Star is just under 15 parsecs away and hasn't been flaring, and spins 131 days, so is deemed 3+Gy old. Planet b only gets 42% incoming flux but that's enough for HZ status on its sun-facing side.
The star probably used to flare which is how come c, just over Earth mass, is blasted out. The paper is going to float implications for the Cosmic Shoreline (to the extent I hadn't already). I don't believe any further planets are detected here; there might not be room below the 25 day range.
What is found here (and not down on c) is "metastable helium". That is the 2 3𝑆1 excited state, bumping an electron to a higher ring; as on WASP-107b. Once excited it takes around 7870 seconds to cool back down again. As Collin Cherubim et al. say in their title, Helium escaping from the atmosphere
(pdf). And the helium isn't always found: it was found 2024 (when this blog was looking) but not 2025.
Also there's not much hydrogen. Although the planet is ill-lit, it should still be warm enough for low-melt methane to rise past the "cold trap" of the convective troposphere (so the paper), where it would be broken up. So no new methane is being created downbelow. Water on the other hand can form into clouds below all that helium. Venerians will pipe in that so can sulfuric acid. Good case for the Sudarsky II.