Moon's Lack of Atmos. vs Titan's Abundance

[danihel]

hello, how come moon is too small to hold any atmosphere and titan has so much atmosphere?

 

[Astronuc]

The moons of Jupiter and Saturn, and for that matter Uranus and Neptune are quite cold because of their distance from the sun. Temperature means that gas molecules do not necessarily achieve escape velocity even in a weak gravitational fields. The further away, the colder the ambient temperature.

Titan (Saturn's largest moon)
Mass 1/45 that of Earth (1.3455 x 1023 kg)
Surface temperature 94K (-180 °C)
Atmospheric pressure at surface 1500 mbar (1.5 times Earth's)

http://www.esa.int/esaMI/Cassini-Huygens/SEMMF2HHZTD_0.html

http://solarsystem.nasa.gov/planets/profile.cfm?Object=Titan


Earth's moon
http://solarsystem.nasa.gov/planets/profile.cfm?Display=Facts&Object=Moon
Mass 7.3483 x 1022 kg

Minimum/Maximum Surface Temperature
Metric: -233/123 °C
English: -387/253 °F
SI: 40/396 K

 

[danihel]

thanks a lot for such a clear answer