Here's who could win the $20 million XPrize for roving on the moon—but will any science get done?

Engineering will determine the ultimate winner of the prize, which is modeled on the Ansari XPrize, awarded in 2004 to give a leg up to cheap human spaceflight. The race to get to the moon, move around, and report back home is meant to foster cheap lunar access so that industry and government agencies can prospect for minerals or build resorts for space tourists. Along the way, though, science will benefit, says Andrew Barton, the prize's director of technical operations in Culver City, California. Movement over the surface and communication with Earth are basic technologies for many future science missions. Also, he notes, the competition offers two bonus prizes that are at least partly scientific. The water discovery bonus ($4 million) requires teams to unambiguously detect water on the surface and publish a peer-reviewed paper to prove it. "Water has been observed from orbit but no one has yet made a physical measurement on the surface," Barton says. For the Apollo Heritage Bonus Prize ($4 million), teams must broadcast video and pictures from one of the Apollo landing sites, and Barton says data on how exposure on the moon has weathered the Apollo artifacts could have scientific value.

None of the potential finalists has declared an intention to look for water. That may be because they're most likely to find it in permanently shady craters at the poles, a difficult place for solar-powered rovers to reach. Nor is it easy to get a look at Apollo relics. Landing on the moon is imprecise, so the nearest Apollo site could lie far beyond the range of the teams' modest rovers. Closer landings risk damage to sites of historical importance, from the blast of a retrorocket or a collision.

Part-Time Scientists, however, is planning to try. The team believes its rovers—developed with the help of the Audi car company—have the necessary range. Karsten Becker, the team's chief technology officer for electronics, says they want to get up close to Apollo 17's lunar rover, which is made of materials including aluminum, fiberglass, nylon, and duct tape. "What's happened to that after 45 years in the space environment? Is it like new or in shreds from micrometeoroids?" he asks. Team Indus from India may go for a smaller, $1 million bonus by visiting the site of an unmanned landing—China's Chang'e 3 lander and Yutu rover, which operated from 2013 to 2014.

Although the bonus prizes haven't generated a stampede to do science, most of the finalists have taken on one or several experiments. SpaceIL's magnetometer aims to help answer the question of where the moon's magnetic field comes from. Is it the relic of an ancient field, created by a churning iron core like Earth's, that was locked into its surface rocks when the core solidified? Or does it come from iron-rich asteroids that generate magnetic fields from the energy of their impact? As the Israeli craft orbits the moon and moves across the surface, the magnetometer will look for correlations between magnetic field changes and impact sites. "This mission may not settle the question once and for all, but we'll make progress," Aharonson says.

Another finalist, Team Indus, is holding an open competition for young people aged 25 and under to devise experiments that could point a way to sustainable settlements on the moon. The team was overwhelmed by 3000 entries from all over the world, including plant and microbial growth experiments, proposals to build lunar structures and radiation shields, and even an attempt to brew beer on the moon. The team recently narrowed the field to a short list of 25, and those groups are now building prototypes that must be the size of a soda can and weigh less than 250 grams. In March 2017, up to eight experiments will be chosen to fly.

Moon Express is carrying a couple payloads: laser retroreflectors from a U.S.-Italian university group to precisely measure the Earth-moon distance for gravitational studies, and a 7-centimeter optical telescope for the International Lunar Observatory Association, a nonprofit aiming to show the power of observing in airless, ever-clear skies. The telescope will have open access for "citizen scientists."

Synergy Moon, an international team with offices in San Francisco, California, aims to blend the arts and sciences—perhaps with a holographic projector that will display artworks on the moon. The team claims it will study weathering of the lunar surface and the nature of the thin atmosphere above it using tiny autonomous robots they call lunar spiders and butterflies. These may be more artwork than instrument, according to a team blog post: "They will also be programmed for swarm behavior, to create random geometric and color patterns."

In general, it's best not to expect major payoffs for science, says Mike Ravine, a project manager at Malin Space Science Systems in San Diego, California, which builds instruments for NASA Mars missions. In 2000, Ravine attempted to get a private moonshot off the ground with BlastOff! Corporation. The effort failed, but it taught him the challenge of trying to do science on a cut-rate mission. If the XPrize teams su succeed, he says, "it would be great to wring some scientific value out of it. But it's a pretty high bar."