1.   Robots might be up to the task sometime in the distant future, making human explorers redundant, he concedes.

2.   Able to grow where nearly nothing else will, they have fed more than their share of caribou and reindeer, not to mention lost and starving human explorers.

3.   But the lawmaker does not attempt to calculate how much it would cost to send human explorers to Mars.

4.   Even if this was not supporting Martian life, the presence of water could be a source of oxygen and fuel for human explorers to the planet.

5.   Extraterrestrial water in any form is considered an invaluable resource for production of oxygen and rocket fuel for human explorers and as a necessary ingredient for life.

6.   Human explorers of these dark ecosystems, working in submersibles equipped with banks of strong floodlights, may inadvertently be blinding the shrimp.

7.   If accessible, water on the moon could serve as a vital resource for human explorers.

8.   If the United States did elect to send human explorers, he believes, the mission could be under way in eight years or less.

9.   McSween, who has served on science teams for several Mars missions, was vice chairman of the panel that assessed potential hazards to human explorers on the planet.

10.   The problem for human explorers is that such regions are frustratingly out of reach.