[tulio_ribeiro]

Didn't know a rocky planet in the habitable zone of a red dwarf could retain atmosphere against intense stellar stripping.

Red dwarfs are known to be cooler (the habitable zone is therefore closer) and unstable.

I don't think LHS 1140b is "Earth-like" at all. Rather, it's more like a mini-Neptune, being boiled off by its star.

Edit: JWST emission spectroscopy of LHS 1140b as it passes behind its star rules out a mini-Neptune. https://arxiv.org/abs/2406.15136

[gcanyon]

The definition of "earth-like" in this context is almost absurdly broad: roughly it means: a rocky-metallic planet, around Earth mass (maybe 0.5 to 1.5 or so?), and in an orbit that might support liquid water -- not has water, just water would be liquid under some circumstances if it were there.

So:

   - no atmosphere? no problem
   - no water? no problem
   - average temperature 40c? fine
   - 4c? Yup

I think both Venus and Mars qualify (barely).

All to say, when someone says a planet is "Earth-like" that doesn't mean we should get out our picnic baskets.

[izend]

LHS 1140 b has about 5.6 times Earth’s mass

[mr_toad]

The host star is described as very inactive, which probably accounts for the retention of atmosphere.

[kazinator]

A really powerful magnetic field could help, also.

Without our field, we would be in trouble, too.

[jjk166]

This is false. Earth's magnetic field does not significantly impact atmospheric loss. For comparison, Venus is closer to the sun and has no magnetic field, but has a substantially thicker atmosphere than earth.

[tonmoy]

I’m not 100% sure I follow what you mean, but here is a link from NASA saying our magnetosphere protects the atmosphere from erosion https://science.nasa.gov/science-research/earth-science/eart...

[rustyhancock]

He's right the magnetosphere doesn't significantly protect our atmosphere. It probably reduces helium loss on earth and other lighter elements.

In addition to his Venus example, Mars lost its atmosphere because it's gravity was too small. Not because it lacks a magnetic field.

[eru]

Venus has lots all her lighter elements in the atmosphere. Basically no hydrogen left (not even in the form of water).

[gregdaniels421]

> Basically no hydrogen left (not even in the form of water).

There should be a decent amount left as sulfuric acid.

[eru]

Yes, confirmed. Though depends on what you mean by 'decent amount'.

[upelephants]

Atmosphere E != Atmosphere V

[PeterHolzwarth]

Pithy rejoinder, thanks! If this were /. in 1999, I'd call this +1 Insightful.

[ErigmolCt]

I went through almost exactly the same thought process reading this :)