NASA on Thursday unveiled an ambitious plan to send eight or more probes to Mars over the next two decades to search for evidence of water or life.

Undaunted by the last year's loss of two red planet explorers, NASA on Thursday unveiled an ambitious plan to send eight or more probes to Mars over the next two decades to search for evidence of water or life. The fleet of orbiters, landers and rovers would employ new technologies that expand their scientific capabilities, save fuel and improve their chances of surviving on the red planet, NASA's chief Mars mission managers said Thursday. n addition to a 2001 orbiter and twin 2003 rovers, all previously announced, the agency plans to send a more powerful orbiter in 2005, a long-range mobile laboratory in 2007 and a new line of "scout" missions that could involve scientific balloons or miniature landers. The first could arrive as early as 2007. The first mission that returns samples of martian soil or rock could launch from Earth as soon as 2011, NASA said. The exploration program "may well prove to be a watershed in the history of Mars exploration," said Ed Weiler, NASA's second in command. In 1999, NASA lost a Mars orbiter and lander, each right before it was to begin its mission. The first most likely burned in the atmosphere because managers failed to convert metric and English measurements. The second presumably crashed moments before landing because of a software glitch. The future orbiters would expand the search for liquid water on Mars, a strong indicator of possible past or present life. Scientists looking at high-resolution images taken by the Mars Global Surveyor announced in June they had identified visual evidence of water just underneath the surface. Surveyor has orbited the red planet since 1997 and can spot features as small as 3 meters (10 feet). The 2005 orbiter will be able to discern objects smaller than one foot.