article image

NASA steps up search for close-passing asteroids

Paul Sutherland, Feature writer
Feb 16, 2014, 8:00 UTC

Sen—NASA has spoken more about its plans to find more asteroids, both to guard against future impacts but also to find a suitable candidate to snag and bring home for a manned mission of exploration.

The agency is to engage in fresh collaborations and also upgrade current search strategies in an Asteroid Grand Challenge to accelerate the rate of discovery of potentially hazardous cosmic missiles.

The need for that was brought home just a year ago by the relatively small asteroid that appeared from a daylight sky and exploded over Chelyabinsk, Russia, causing extensive damage and injuring thousands of people, mainly due to flying glass.

But work will also be focused on identifying a Near Earth Object that will make a good target for the Asteroid Redirect Mission that will be the first to capture a suitable rock and bring it into a safe orbit around the Moon where it can be visited by astronauts in the 2020s.

NASA is currently developing the hardware for such a mission, including its new Orion spacecraft, the Space Launch System (SLS) rocket, and high-power Solar Electric Propulsion.

The agency says it is looking at two options for snaring an asteroid for the project. One is to locate a very small asteroid that can literally be bagged and brought complete by a robotic craft to lunar orbit. The other is to collect a large boulder from the surface of a larger asteroid and steer that here instead. Astronauts could then study it and bring back samples for scientists to analyse.

Chelyabinsk super-bolide

The trail left by the Chelyabinsk super-bolide that exploded in the atmosphere over Russia a year ago. Credit: Alex Alishevskikh. CC BY-SA 3.0

One might imagine that NASA has plenty of asteroids already to choose from because many are known that come close to intersecting our own planet’s orbit. In fact, very few of those are suitable, either because they are too big or because they are in orbits that would make it difficult to bring them to the Moon.

Those that are the right sort of size tend not to be visible for long when they come close. To help learn more about them while they are, NASA has come up with a rapid response system. This will seek to check out their size and characteristics swiftly using the radar capabilities of giant radio telescopes.

Paul Chodas, a senior scientist at the Near-Earth Object Program Office based at NASA’s Jet Propulsion Laboratory, in California, said: “There are other elements involved, but if size were the only factor, we’d be looking for an asteroid smaller than about 40 feet (12 meters) across.

“There are hundreds of millions of objects out there in this size range, but they are small and don’t reflect a lot of sunlight, so they can be hard to spot. The best time to discover them is when they are brightest, when they are close to Earth.”

NASA estimates that tens of asteroids of this size fly past us closer than the Moon each year but that the vast majority go undetected, sometimes because they are invisible in the daylight sky unless they hit us like Chelyabinsk.

Most asteroids are found by various surveys of the night sky, involving either humans or robotic telescopes, which scan the heavens for fast-moving, star-like objects. Alerts to potential discoveries are sent to the Minor Planet Center at Cambridge, Massachusetts, which checks it out before adding it to its database. This process was updated last year so that possible candidates for the ARM mission can be identified.

Chodas explained: “If an asteroid looks as if it could meet the criteria of size and orbit, our automated system sends us an email with the subject ‘New ARM Candidate’. When that happens, and it has happened several dozen times since we implemented the system in March of 2013, I know we’ll have a busy day.”

When a likely candidate is found, Chodas calls scientists at NASA’s Deep Space Network station at Goldstone, California, and the Arecibo Observatory in Puerto Rico, to check that the telescopes are available to track the object with radar. He may also alert selected professional or well-equipped amateur observatories to provide photographic data.

The hunt for asteroids is being enhanced in other ways too. One leading Nasa-funded search, called the Catalina Sky Survey, is getting an upgrade, and new survey telescopes will become available such as PanSTARRS 2 and ATLAS, and the Defense Advanced Research Projects Agency’s new Space Surveillance Telescope. NASA’s WISE spacecraft has been reactivated and renamed NEOWISE to find asteroids too.

NASA already spending $20 million a year searching for potentially hazardous asteroids through the Near Earth Object Observation Program. This year’s budget included $105 million to plan for the capture and redirection of an asteroid.

NASA and other national space agencies, including ESA, have also set up a high-level group, mandated by the UN, to help coordinate a global response should a threatening asteroid be found heading for Earth. It held its first meeting at Darmstadt, Germany, on 6-7 February.

More than 600,000 asteroids are known in our Solar System, with more than 10,000 classified as near-Earth objects, or NEOs, because their orbits bring them relatively close to our own.