SAN FRANCISCO (Reuters) - Google executive chairman Eric Schmidt and billionaire co-founder Larry Page have teamed up with "Avatar" director James Cameron and other investors to back an ambitious space exploration and natural resources venture, details of which will be unveiled next week. The fledgling company, called Planetary Resources, will be unveiled at a Tuesday news conference at the Museum of Flight in Seattle, according to a press release issued this week. Aside from naming some of the company's high-profile backers, the press release disclosed tantalizingly few details, saying only that the company will combine the sectors of "space exploration...