A decade ago, in a strikingly forward-thinking move, the US Congress passed a law requiring NASA to identify 90 percent of asteroids that were 140 meters across or larger and could potentially threaten Earth. Congress gave NASA a deadline of 2020 to meet that goal, but the agency will fall far short of that target. The agency has a valid excuse: it never received funding to meet this goal.

Now, however, there is some hope for finding killer asteroids. The National Science Foundation has backed the Large Synoptic Survey Telescope (LSST) in Chile, and NASA is considering funding NEOCam, a space-based infrared telescope that would specialize in identifying potentially hazardous asteroids. But scientists weren't quite sure how these two instruments would fare in a concerted hunt for large asteroids.

A new pre-print on arXiv offers some clarity, and the answer appears to be that the ground-based and space-based approaches will complement one another nicely. According to a new simulation of near-Earth threats and the capabilities of these two instruments, neither the ground-based telescope nor NEOCam would come close to finding all of the potential hazards on their own. However, when combined, they were projected to find a little more than 90 percent of the threats.

"The advantages of operating both NEOCam and LSST are many," the authors write. They will observe complementary regions of space, and because LSST will use optical light—whereas NEOCam observes in the infrared—they will get better size, albedo, and color information on these asteroids and gain a better understanding of their composition, a key determinant of the overall threat posed by a large asteroid.

The study, which has been accepted for publication in the Astronomical Journal, was led by Tommy Grav, a planetary scientist with the Planetary Science Institute. He and another co-author, Amy Mainzer, are principal investigators of the NEOCam mission, which NASA is considering as one of five finalists for full funding as part of its Discovery program.