To distinguish themselves from astronomers. ;-)

__________________
Rovers forever! - ToSeek
"Carl Sagan sent a message to ET,
Neil Armstrong walked in the Sea of Tranquility
Steve Squyers built Spirit and Opportunity
Dan Haylen upchucked in zero gravity." -Brent Simon, The Space Camp Song
'Evolution and science are one thing, but you don’t mess with Yoko Ono. Everybody knows that. ' - 386sx