WASHINGTON — NASA’s No. 2 official has identified an asteroid that could be visited by U.S. astronauts in a mission that U.S. President Barack Obama has targeted for launch around 2025.

In an April 26 speech at the Center for Strategic and International Studies here, NASA Deputy Administrator Lori Garver said a five-month round-trip mission to asteroid 1999 AO10 could be launched by the middle of the next decade, though she added that alternative near Earth objects (NEOs) could be considered in the interim.

“We’re discovering new NEOs all the time, so our list of targets will certainly grow over the coming years, but one intriguing candidate is asteroid 1999 AO10, which we could reach with a 2025 launch on a 150-day round-trip mission which would allow us to spend about two weeks at the asteroid,” Garver said.

Asteroid 1999 AO10 was discovered in January 1999 using a pair of Ground-based Electro-optical Deep Space Surveillance telescopes at the Massachusetts Institute of Technology’s Lincoln Laboratory test site at White Sands, N.M. It is estimated to be 50 to 110 meters in diameter.

In his April 15 space policy speech at NASA’s Kennedy Space Center, Fla., Obama said his vision for NASA would have U.S. astronauts launch in 2025 on a manned mission to an asteroid, though he offered few details beyond pledging to “test and prove the systems required for exploration beyond low Earth orbit” in the coming years.

Obama’s plan proposes scrapping NASA’s Moon-bound Constellation program but retaining a scaled-back version of its Orion crew capsule for use as an escape pod aboard the international space station and potentially as a future deep-space capsule. His call to send humans to a near Earth asteroid lifts a page from a 2006 study funded through the Constellation program office.

The study, led by NASA’s Ames Research Center in Mountain View, Calif., Johnson Space Center in Houston and Jet Propulsion Laboratory in Pasadena, Calif., drew up a list of dozens of asteroid candidates reachable within six months using Constellation hardware. It determined, among other findings, that Orion could be launched atop an Ares 5 heavy-lift rocket on a 150-day mission to 1999 AO10 as early as August 2025.

The Ares 5, along with the smaller Ares 1, is marked for cancellation under the president’s plan.

“The most significant advantage of piloted missions to a NEO is that it strengthens the foundation for the Vision for Space Exploration and Exploration Systems Architecture Study in the run up to the lunar sorties and Moon base development beginning at the end of the next decade (~2020),” the study states, referring to former President George W. Bush’s 2004 plan to return humans to the Moon by 2020. The Exploration Systems Architecture Study followed, ultimately leading to Constellation’s implementation.

Piloted missions to a near Earth object were discussed in 1966 as a potential use for the Apollo spacecraft and Saturn 5 hardware, which potentially could have reached the asteroid 433 Eros. Two decades later, NASA reconsidered asteroid visits as part of the 1989 Space Exploration Initiative, which never got off the ground, and since then four additional NASA studies have examined the idea.

To date, two unmanned spacecraft have explored asteroids: NASA’s NEAR Shoemaker spacecraft visited 433 Eros in 1999, and Japan’s Hayabusa probe reached 25143 Itokawa in 2005.

NASA is considering a Discovery-class mission proposal dubbed the Origins Spectral Interpretation Resource Identification Security-Regolith Explorer. That probe would take three years to rendezvous with a target asteroid, where it would spend several months gathering data before returning with a sample two-and-a-half years later.

In her speech, Garver said that before NASA sends humans to 1999 AO10 — or any other asteroid — the agency plans to send robotic precursor missions to such destinations, an approach detailed in the Constellation study.

“We know very little about this particular one, 1999 AO10, potentially our most promising target at this time, and this is where our exploration precursor robotic missions come into play,” Garver said. “With these missions we can explore potential candidates and provide ground truth for our Earth-based telescopic observations of NEOs. These are the tangible reasons for making NEOs one of our first destinations for humans in deep space.”