Will Apophis Hit Earth?

  • By David Levin
  • Posted 09.01.06
  • NOVA scienceNOW

Why can't scientists tell us for sure whether the stadium-sized asteroid Apophis will hit Earth? In this riff on the nature of scientific uncertainty, astrophysicist Neil deGrasse Tyson explains.


Hear exactly why scientists seem wishy-washy in their predictions about Apophis.


Will Apophis Hit Earth?

Posted September 1, 2006

DAVID LEVIN: You're listening to a NOVA scienceNOW podcast.

2036 could be a bad year for Earth. That's when Apophis, a stadium-sized asteroid, might plow into the Pacific Ocean, or it might miss us entirely. NOVA producer Joe McMaster talked with scienceNOW host Neil deGrasse Tyson about why the odds keep changing and why that shouldn't be surprising.

JOE McMASTER: So Neil the predictions about the likelihood of Apophis hitting Earth seem to keep shifting. Why can't these astrophysicists just make up their minds? Are they just being wishy-washy?

NEIL DeGRASSE TYSON: Yep. [Laughs] Occasionally wishy-washy is what you have to be when you're waiting eagerly for better data to come down from space. As you know the orbit to better and better precision, you can then say, with confidence, what it will do as it comes near Earth, and right now we don't have that ability. What we're planning, though, is to send a mission to Apophis and put a transponder on it. A transponder is kind of like a cosmic Lojack system. Where it's a little device that transmits the location of Apophis at all times back to us. So we will know within a centimeter what Apophis is doing.

And if you can do that over a long enough baseline of time, then you can calculate an orbit with very high precision. And then you'll know whether it's going to hit Earth or not. And then we don't have to say, "Oh, it's a 20 percent chance …" They'll say, "It's a hundred percent chance it won't hit Earth, or it's a hundred percent chance it will."

JOE McMASTER: These probabilities you're talking about sounds a little bit like a way for scientists to hedge their bets at this time.

NEIL DeGRASSE TYSON: I don't like to think of scientists as betting, but it is a hedge. We're hedging our uncertainty. By the way, when you're on the frontier of science, that's the place you do this. Because you're still waiting for better and better data to sharpen your predictions. Once you have perfect data, and you know exactly what's going to happen next, it's no longer an interesting scientific problem, and you move on to the next frontier where you end up hedging your bets again.

So when you hear a scientist speaking with great uncertainty, that scientist is speaking to you from the frontier of our understanding of the universe, and that's where any good scientist wants to be. So we should celebrate the uncertainty and work hard to try to get the latest data so that we can tie a bow on that scientific problem and move on to the next one.

DAVID LEVIN: To learn more about Apophis, watch the October 3 episode of NOVA scienceNOW.



Produced by
David Levin
Interview by
Joe McMaster


© NOVA/WGBH Educational Foundation

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