DAVID GREENE, HOST:
Last night, our planet had a pretty close call. A large space rock capable of causing some damage whizzed past Earth, missing by a mere 300,000 miles. That is nothing in astronomical terms. NPR's science correspondent Joe Palca reports on what NASA is doing to prevent these so-called near-Earth objects from hurting us.
JOE PALCA, BYLINE: The first thing NASA is trying to do about near-Earth objects is to find them.
PAUL CHODAS: The NASA surveys are finding something like at least five asteroids every night.
PALCA: That's astronomer Paul Chodas of NASA's Jet Propulsion Laboratory in Pasadena. NASA pays for several telescopes to routinely scan the skies, looking to see what's new out there. But then the trick is to figure out which new objects might hit the Earth.
CHODAS: When a telescope first finds a moving object, all you know is that it's just a dot moving on the sky. You have no information on how far away it is.
PALCA: There's a lot of uncertainty at first. NASA's Davide Fornacchia says the more telescopes you get pointed at an object, the more images you get, and the more you're sure how big it is and which way it's headed. But sometimes you don't have a lot of time to make those observations.
DAVIDE FORNACCHIA: Objects can come close to the Earth shortly after discovery sometimes - one day, two days or even less - even hours in some cases.
PALCA: So that's why Fornacchia and his colleagues have come up with a computer program they call Scout.
FORNACCHIA: The main goal of scouting is to speed up the confirmation process.
PALCA: Scout soaks up data from telescopes around the world. It makes a quick and dirty estimate of anything that has even a small chance of hitting Earth. If it finds something, it sends an alert to Fornacchia and his colleagues, and they can ask astronomers around the world to study the object to help them quickly decide whether it's a real threat.
That's what happened in the case of the space rock that flew by Earth last night. It was discovered by a telescope in Hawaii last Tuesday. Scout flagged it as something deserving further attention. Three telescopes in Arizona also took images of the object. The new data from those telescopes showed the rock would safely pass us by.
Scout is still on the testing phase. It should become fully operational later this year. Now, Scout is mainly dealing with smallish, very nearby objects. Complementing Scout is another system already operational called Sentry. Paul Chodas says Sentry's job is to identify large objects that might hit the Earth in the next hundred years. And by large, he means objects capable of obliterating a major city.
CHODAS: Our goal right now is to find 90 percent of the 140-meter asteroids and larger.
PALCA: Well, how close would you say you are to that?
CHODAS: We're at about 25 to 30 percent of the estimated population.
PALCA: That number should get better when a new telescope being built in Chile comes online. And NASA is also considering a space telescope devoted to searching for asteroids. OK, so let's say you find one of these monster rocks heading for the Earth, what then? Astronomer Ed Lu says there is something you can do. He's CEO of an organization called B612. It's devoted to dealing with asteroid threats.
ED LU: If you know well in advance - and by well in advance, I mean, you know, 10 years, 20 years, 30 years in advance - then you can divert such an asteroid by just giving it a tiny nudge when it's still many billions of miles from hitting the Earth.
PALCA: NASA and the European Space Agency are developing a mission to practice doing just that. Joe Palca, NPR News.
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