This is the most surprising news I've heard in years!

Old data from the SoHo spacecraft show that Earth's exosphere reaches far longer into space than anyone had ever imagined: 391,000 miles! That's way beyond the Moon!

https://www.sciencealert.com/earth-s-atmosphere-is-so-big-that-it-actually-engulfs-the-moon

I don't know if this is "Wow!" or "WTF?!" news, but it's up there.

Okay, here's the question that I just need to ask, even though I know the answer will be a hard "no"!

If the Earth and Moon can hold on to such a large cloud of hydrogen atoms, couldn't a galaxy do the same? And (here comes the criminal part) could it account for dark matter?

7 minutes ago, QuantumT said:

Okay, here's the question that I just need to ask, even though I know the answer will be a hard "no"!

If the Earth and Moon can hold on to such a large cloud of hydrogen atoms, couldn't a galaxy do the same? And (here comes the criminal part) could it account for dark matter?

I suppose the best way to answer that is that Earth/Moon space is far less tenuous then interplanetary space, which again is less tenuous then interstellar space, which in turn is less tenuous then intergalactic space.

36 minutes ago, beecee said:

I suppose the best way to answer that is that Earth/Moon space is far less tenuous then interplanetary space, which again is less tenuous then interstellar space, which in turn is less tenuous then intergalactic space.

Yes of course. Silly me. Thanks!