Planetary science. Europa vs. Titan.
Kerr
Richard A
RA
D018559:Exobiology; D005118:Extraterrestrial Environment / Q000737:chemistry; D018538:Jupiter; D018539:Saturn; D013026:Space Flight / Q000191:economics; D018531:Spacecraft; D014481:United States; D018557:United States National Aeronautics and Space Administration / Q000191:economics; D014867:Water
D014867:Water