http://www.helium.com/knowledge/5908-determining-whether-its-necessary-for-man-to-go-to-mars.xml Helium.com > Astronomy > Determining whether it's necessary for man to go to Mars en-us Copyright Helium.com Mon, 05 May 2008 19:39:55 GMT Mon, 05 May 2008 19:39:55 GMT