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Comment by heavyset_go | Hacker News Reader

> It’s hard to imagine with the amount of H2O on the planet right now, but if it can happen to Mars (the atmosphere is stripped away), it could happen here I suppose.

Mars' atmosphere isn't protected by a strong magnetic field because the planet isn't geologically active, unlike the Earth. Gasses escape from the Earth into space constantly, but not at a rate that will leave the Earth like Mars before the sun becomes a red giant.

In billions of years, the sun will expand and probably blast away the Earth's atmosphere before possibly engulfing it later.

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The Earth will lose its oxygen first, then enter a moist greenhouse. This is all long before the sun becomes a red giant.

https://phys.org/news/2021-03-simulations-earth-oxygen-rich-...

(the summary there is inaccurate; CO2 will be increasingly absorbed by weathering of rocks as the Earth heats, until photosynthesis fails and oxygen levels collapse.)

Nice, thanks for the link.

I'm no astrophysicist, but I'm under the impression that the effect of the magnetosphere is popularly overstated. Rather, the reason that Earth still has its atmosphere and Mars doesn't is that Earth has the gravity to hold onto it more tightly, and Mars is just too small. Hence why Venus, which also (curiously) has no dynamic magnetosphere, still has an atmosphere: it's 80% the mass of Earth (compare Mars, which is 10% the mass of Earth).

The death of Mars' magnetosphere allowed solar wind plasma to strip away its atmosphere in the past[1]. Mars once had a much denser atmosphere when its dynamo was active, and the stripping of its atmosphere happened when the dynamo died.

[1] http://redplanet.asu.edu/?p=2035

Titan is ~Mars-sized, yet it has an atmosphere thicker than that of the Earth.

It may be safe to say that both factors are at play, here.

Titan is largely protected by Saturn's powerful magnetosphere, which does a lot to help, I imagine.

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