Wanted: a flat, mineral-rich plot - with Earth view

When it comes to picking a spot to send the first humans to the moon in more than 40 years, the old real estate refrain still rings true: It's location, location, location.

For Mark Robinson's money, the Aristarchus Plateau - a prominent feature on the moon's near side - is an attractive candidate.

"It's a great place to go," says the Northwestern University planetary scientist. Its dramatic moonscape is a geologist's playground. Just as important, new Hubble Space Telescope data he's gathered confirm that the region contains a key mineral. And the data could resolve the debate over whether there's enough of it to help lunar explorers live off the land.

That's the picture that emerges from an experiment to see if looking at the moon through ultraviolet eyes - in this case, Hubble's - can help planners pick landing sites with the "right stuff" to support human exploration.

The results, announced Wednesay by NASA, represent the opening round of efforts to prepare to send astronauts to the moon by 2020, a key objective in President Bush's vision for space exploration. It also takes place against a backdrop of growing international efforts to get up close and personal with Earth's companion. The European Space Agency currently has a small craft orbiting the moon. India and China are planning to launch lunar orbiters in 2007. Japan is inching ahead on its long-anticipated mission to study the moon.

"Interest has really grown in the last five years," says Carle Pieters, a planetary scientist at Brown University in Providence, R.I., who is building an instrument for India's lunar mission.

To nations such as China and India, these missions are natural next steps. They have a strong national-prestige component, specialists say. And they lay the foundation for joining the small club of countries capable of pulling off deep-space spectaculars, such as sending probes to unlock secrets of distant planets.

These nations "recognize that the moon is reachable and well within their capabilities," says Paul Spudis, a planetary scientist at The Johns Hopkins University's Applied Physics Laboratory in Laurel, Md. The projects "are a good way to acquire the capacity to do deep-space missions."

For the US, the key driver is Mr. Bush's blueprint for space exploration. The first dedicated mission to support the lunar portion of the program is an orbiter slated for launch in 2008. Among its objectives: to provide maps, images, and other information in sufficient detail to allow planners to gauge the potential hazards of possible landing sites. And it will gather high-resolution information on minerals visible on the surface.

Indeed, the Hubble experiment was designed in large part to test the idea that ultraviolet-based data could help locate key minerals. The Clementine spacecraft in the early 1990s had used infrared and visible light to detect ilmenite, a mineral loaded with iron, titanium, and oxygen. But the results didn't give scientists a clear idea of how much was there. The ultraviolet data will help offer a more precise inventory, Dr. Robinson says.

Currently, NASA has its sights set on two precursor science missions: the 2008 Lunar Reconnaissance Orbiter and a lander the agency would like to launch in 2010 or 2011, notes Michael Wargo, a NASA lunar scientist.

More are likely to follow, although the number and timing is unclear at this stage, Dr. Spudis adds. Much will hinge on the results from the first two.

Many in the planetary science community worry that these precursor missions could draw resources from other solar- system research.

"Though there are interesting scientific questions concerning the moon that deserve further study, there are many more interesting places to focus on," says Joseph Veverka, who heads the astronomy department at Cornell University. "We need to have a balanced approach.

Even so, two modest missions in the 1990s forced many scientists to shed their blasé attitude toward the moon following the detailed study of moon rocks the Apollo astronauts brought home, notes Dr. Pieters. The Clementine and Lunar Prospector missions revealed deeply puzzling features.

On the far side of the moon, Clementine revealed a crater stretching from the moon's south pole nearly to the equator. This enormous feature holds the deepest and highest spots on the lunar surface and presents scientists with a unique window on the moon's geological evolution. From Lunar Prospector came evidence that heat-producing elements such as uranium and thorium are largely distributed in lopsided fashion. On Earth, by comparison, these elements are largely concentrated at the core. And Lunar Prospector revealed an abundance of hydrogen in craters at the poles, leading to a debate over whether the hydrogen represents water - a precious resource - or merely hydrogen spewed from the sun.

Given the range of international missions destined for the moon over the next five years, answers to some of these puzzles may not be far off.

"This is going to be a really exciting decade for the moon," Pieters says. "It's just getting started."