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NARRATOR: Making sure the sky is NOT falling.
I'm Jane Platt with a podcast from JPL -- NASA's Jet Propulsion Laboratory in Pasadena, California.
Asteroids and comets are pretty cool, cosmic objects -- as long as they keep their distance. Dr. Steve Chesley of JPL is with NASA's Near Earth Object office, which uses telescopes and radar to study objects that venture near Earth.
CHESLEY: Well, we have about 4,300 Near Earth objects in the catalog at the moment. That's all sizes. We're most interested in finding the large objects, what we consider to be those that could, say, threaten the climate of the Earth if they were to impact.
NARRATOR: Those are bigger than one kilometer, or four times the size of Pasadena's Rose Bowl. Scientists have found more than 700 of those. Most are too far away to pose any danger to Earth. On the other hand, they have identified about 120 objects -- of varying sizes -- that do have the potential to hit Earth. Still, no need to panic.
YEOMANS: No one knows of a friend or a loved one who has been hurt by a Near Earth object, that's true. So these are very low probability events but very high consequence events. It's very unlikely that one of these large objects will hit us.
NARRATOR: Dr. Don Yeomans heads NASA's Near Earth Object office. His colleague, Dr. Steve Chesley, says an ounce of prevention is worth a pound of cure.
CHESLEY: NASA's approach to the Earth hazard problem so far, and I think rightly, has been to focus on discovery. You can not deflect an object that you haven't discovered. And so finding the asteroids, finding them early is the most important thing in this process.
NARRATOR: So the Near Earth Object office, with input from astronomers around the world, detects objects, tracks their location, size, speed and movement over a period of time. They rate them on the 10-point Torino scale. Sort of like the Richter scale for earthquakes.
CHESLEY: Torino scale zero is where 99 percent of our cases fall, which means it's just not worth any public attention, although we continue to monitor those routinely.
Torino scale one means it's more than ordinary, but still not particularly alarming. We get on average a few, maybe several Torino scale one cases per year. We have had a couple of Torino scale twos. We even had one Torino scale four, which was quite extraordinary.
NARRATOR: Now a four is enough to worry about. But with more detailed observations, the four and the twos were downgraded.
CHESLEY: After an object is discovered and observations continue to arrive at our office, we continue to update and refine the orbital predictions and the impact assessments. That allows us to refine the Torino scale ratings for the object and so on.
Narrator: And so far, every single worrisome object they've tracked, with further observations, has been ruled out as a hazard to Earth. Interested in keeping tabs on these objects? Check out the Near Earth object website at http://neo.jpl.nasa.gov .
CHESLEY: We have the impact probabilities, and you can click on any one of the objects and get details. But at the top level, there's a summary for each object. The speed at which it passes the Earth is present there, and that of course is important for the impact energy. The size of the object, and the Torino scale.
NARRATOR: Again, that's http://neo.jpl.nasa.gov , and it includes a lot of links. Oh, and in case you're wondering what would happen if scientists did find an asteroid that really could threaten Earth? Researchers are scoping out different ways to handle a scenario like that.
CHESLEY: Probably the best and most obvious way of deflecting an asteroid is to simply slam another, a spacecraft, into it, and to slow it down, or speed it up if you overtake it from behind, and that gives it enough change in velocity to steer it off the Earth impact trajectory.
NARRATOR: But again, none of the known near-Earth objects have scientists staying up nights worrying. So for now, they say -- the sky is not falling.
Thanks for joining us for this podcast from NASA's Jet Propulsion Laboratory.
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