Ice on Moon?
Why surprising:
- consider escape velocity (2.4 km/s) -- low
- if thermal velocity of an atom or molecule exceeds this, it will escape
- Thermal velocity governed by temperature and mass
- hotter molecules are moving faster
- lighter molecules are moving faster
- thermal velocity of N2 molecules in this room (~ 300 K) about the speed of sound (300 m/s)
- T of Moon determined by energy balance
- sunlight absorbed = thermal emission
- thermal emission ~ T4 for blackbody
- Presence of an atmosphere
- evens out day/night and equator/pole variation