AUSTIN, Texas — Mining asteroids for water and other resources could someday become a trillion-dollar business, but not without astronomers to point the way.

At least that’s the view of Martin Elvis, a researcher at the Harvard-Smithsonian Center for Astrophysics, who’s been taking a close look at the science behind asteroid mining.

If the industry ever takes off the way ventures such as Redmond, Wash.-based Planetary Resources and California-based Deep Space Industries hope, “that opens up new employment opportunities for astronomers,” Elvis said today in Austin at the annual meeting of the American Association for the Advancement of Science.

In space, the water in asteroids can be more precious than gold — largely because it costs thousands of dollars per pound to launch supplies from Earth. That water could be used to produce oxygen and drinking water for astronauts, plus the propellants for refueling rockets.

Other materials may come in handy for use as in-space building materials. But not all asteroids are created equal: Most space rocks will be worthless, Elvis said.

“To find the few percent of valuable asteroids, we can ask astronomers, using ground-based or mountaintop telescopes, and greatly narrow down the search,” he said. “We can save 90 percent of the cost of expeditions out to particular asteroids.”

Providing that guidance will require a “new band of applied astronomers” who are trained to identify the best prospects for mining, Elvis said. He said some of his colleagues in academia have already set up a stealthy startup aimed at acquiring astronomical data and selling it to asteroid miners — but he declined to provide further specifics.

Asteroid mining is more than a blue-sky idea: Planetary Resources is testing a prototype space telescope that was launched into Earth orbit last month, and the company has said it could start using more advanced telescopes to scout for asteroids within the next couple of years.

Deep Space Industries, meanwhile, is working with Luxembourg’s government to get its Prospector-X prototype spacecraft off the ground, and last year it received two NASA technology development grants.

Both companies have announced plans to start mining asteroids in the 2020s.

The fact that the companies have devoted millions of dollars to in-house spacecraft development might suggest that they’ll draw upon in-house astronomical expertise as well. But Elvis said Planetary Resources and Deep Space Industries are currently focused on the engineering challenges rather than the scientific tasks that will follow.

“Right now, my impression is that both companies are somewhat underestimating their needs for astronomers,” he said.

Elvis voiced confidence that there’ll be enough astronomers interested in asteroid hunting to fill the need.

“Occasionally, over the 30 years I’ve been at the Harvard-Smithsonian Center for Astrophysics, I’ve had a Harvard undergraduate come to me and do a project on supermassive black holes, which is my normal beat,” he said. “As soon as I started advertising working on little rocks nearby, I’ve had them banging on my door every semester, wanting to work on it.”