Polar ice on Mercury

[james_davis_nicoll]

Mercury's north pole has frozen water according to data revealed Thursday by NASA scientists, confirming the long-held suspicion that the very hot planet closest to the Sun has ice lurking in the shade.

Comments

[ilya187.livejournal.com]

It's too bad the liquid helium critters could not exist. No surface of a planet is going to be colder than the temperature of the microwave background radiation, and the vapor pressure of liquid helium at that temperature is still quite high (more than .1 bar.)

This excludes Mercury, but not larger (and more helium-rich) planets. What's so impossible about 0.1-0.2 bar helium atmosphere, and thus not-evaporating helium critters?

[neowolf2.livejournal.com]

They could not exist where Niven had them, I meant.

Also, if a planet is large enough to retain a helium atmosphere, I think the internal heat flow would be great enough to raise the surface temperature above the boiling point of helium.

[rwpikul.livejournal.com]

Solar wind and photon bombardment causes helium to boil off into interplanetary space. Hydrogen would suffer the same fate except that it tends to form water in the atmosphere and is kept out of the upper atmosphere because it freezes out.