Why haven't astronauts traveled to Mars?
http://www.worldbook.com/world-book-e...
"Are there dangers in traveling to Mars? Jeff De La Rosa, Managing Science Editor at World Book Encyclopedia, explains why astronauts have not yet travelled to Mars.
Find out more about astronauts at http://www.worldbook.com/world-book-e...
Videos are produced and directed by Jennifer Parello for World Book Encyclopedia."
