AILSA CHANG, HOST:
All right, this is just a drill. Picture an asteroid; it's been detected hurtling towards the Earth, just eight years from a possible impact. Again, this is not real, people, but it was a scenario that scientists grappled with all this week at a planetary defense conference held outside of Washington, D.C. Here to tell us more about whether Earth survived is NPR's science correspondent Nell Greenfieldboyce. Hey, Nell.
NELL GREENFIELDBOYCE, BYLINE: Hey.
CHANG: I assume we did survive.
GREENFIELDBOYCE: We're still here.
CHANG: OK. So remind us what this meeting was all about this week.
GREENFIELDBOYCE: So this was a planetary defense meeting. So this is all about asteroids. And the people who came to this meeting were from all over the world - they were scientists, engineers, people who know how to track asteroids and send missions to them and try to deflect them off course. Also, there were a bunch of emergency managers. And so every couple of years all these people come together, and they have a kind of drill or exercise to play out scenarios, and this time what they were doing was contemplating an asteroid about 300 to 1,000 feet across that could strike the Earth.
CHANG: Whoa. OK, so walk us through what an exercise like this would look like.
GREENFIELDBOYCE: So at the beginning of the week, on Monday, they were tracking it with telescopes. Remember - this is all fiction.
GREENFIELDBOYCE: And there was only a 1% chance of hitting the Earth in eight years. But by Tuesday, that had gone up to a 10% chance of hitting the Earth, so they sent a spacecraft out to study it. Now, with more detailed information from that mission, they established that it was going to hit near Denver, Colo. Like, it absolutely was going to hit near Denver, Colo. So they sent out this whole fleet of spacecraft built by all the world's major space agencies - so Russia, Europe, China, Japan and, of course, NASA. And they were going to try to change the trajectory by basically running into it.
CHANG: Like hitting it.
GREENFIELDBOYCE: Yeah, yeah. And so some of those missions failed. Some did hit the asteroid, but unfortunately, this fractured the asteroid into two pieces.
CHANG: Wait, so the asteroid split in half?
GREENFIELDBOYCE: Yeah. Yeah, and that could happen.
GREENFIELDBOYCE: And so in this scenario, now one piece was headed away from Earth, but one fragment was definitely going to hit, and now it was possibly going to hit the East Coast of the United States.
CHANG: Was there any time left to try something else?
GREENFIELDBOYCE: So there was this short window when they could have tried to send a nuclear device to kind of blast it to bits, but they couldn't pull it off, and they just ran out of time. And so today was the final day of the exercise, and everyone learned that the 200-foot fragment was headed right towards New York City. It was going to hit the atmosphere over Central Park at high speed and explode.
CHANG: How much damage would that cause?
GREENFIELDBOYCE: So that would basically obliterate most of - that would obliterate Manhattan; like, Manhattan would mostly be gone.
CHANG: Sorry. Sorry, New York. All right, so how much warning would New York City have had in this case?
GREENFIELDBOYCE: Only a couple of months' notice that it was definitely going there. And so that's a couple of months, but you need to get 10 million people off an island.
GREENFIELDBOYCE: And then there's all the artwork in the museums and disruption to the financial district. And keep in mind - this is not a normal evacuation in the sense that people will be going back to their homes.
GREENFIELDBOYCE: Because their homes are not going to be there. I mean, everything's just going to be kind of vaporized.
CHANG: Vaporized, OK. So as we keep repeating, listeners, this is just a fake scenario. But Nell, how likely is it that something like this would ever happen?
GREENFIELDBOYCE: So this is very, very unlikely. I mean, asteroids this size do not strike Earth that often, and an asteroid would be more likely to hit in the ocean than a major U.S. city.
GREENFIELDBOYCE: But still, you know, they play out these extreme scenarios to kind of look for weaknesses in the system. Like, what would happen if you tried to deflect an asteroid from one area and ended up aiming it someplace else?
CHANG: That's NPR science correspondent Nell Greenfieldboyce talking to us about a fake, purely hypothetical scenario that was played out this week at a planetary defense conference. Thanks, Nell
GREENFIELDBOYCE: Thank you. Transcript provided by NPR, Copyright NPR.