Scientists think big impact caused two-faced Mars - Yahoo! News

Scientists think big impact caused two-faced Mars - Yahoo! News: "Scientists think big impact caused two-faced Mars By ALICIA CHANG, AP Science Writer
1 hour, 7 minutes ago


LOS ANGELES - Why is Mars two-faced? Scientists say fresh evidence supports the theory that a monster impact punched the red planet, leaving behind perhaps the largest gash on any heavenly body in the solar system."