Last month, this article was published on the website of the Express, a tabloid paper in the U.K. A few days later, Phil Plait caught wind of it and debunked the article on his Bad Astronomy blog at Slate.com. Essentially, the author of the Express article completely misinterpreted the real data on a newly discovered asteroid, turning this one object into an entire unknown asteroid belt that would wreak repeated havoc on the Earth over the next century. I don't want to repeat Phil's excellent analysis of the situation and how the original author got it so wrong. I just thought I'd bring some simple visualization to bear on the problem, and maybe do a little educating.
The asteroid is 2014 NZ64, and it was discovered on July 3, 2014. It was observed 4 times that night by the Pan-STARRS survey in Hawaii, and then 4 more times on July 5th by my friends at the Astronomical Research Observatory in Illinois. Eight observations over two days, that's it! That's not very much to go on. In fact, the Minor Planet Center says that by July 9th, its predictions were so uncertain that you wouldn't be guaranteed to see the asteroid within a typical telescope's 10-arcminute field of view. And by the article's publication on Sept. 5th, the uncertainty radius had increased to 75 degrees. That's half the sky!! So it's pretty crazy to say we know much about this asteroid at all.
On the other hand, we do know it was seen on those two nights, and we can do our best to extrapolate its motion from there. But we need to be honest about how good those extrapolations are! So we won't just fit one orbit to the observations, but many orbits, and we'll use them to map out our uncertainties. See my previous posts for more discussion about my methods. Let's jump straight to the results! In the animation and simulation below, the best-fit orbit of the asteroid is shown in bright blues, with the alternate possible orbits shown in faded colors. The portion of each orbit that is "above" the plane of the solar system is colored cyan, while the part "below" the plane is darker blue.
The animation starts on July 5th, during the very short time period when the asteroid was observed. See how the possible positions of the asteroid on this date all line up to point directly away from the Earth? As I love to say, "Astronomers have horrible depth-perception!" At that point, we knew how to point in the direction of the asteroid in the sky, but we had very little idea of how far away it was. We had the best-fit position of the asteroid, but as you can see, the distance was quite uncertain. And as time goes on, Kepler's 3rd Law causes the potential orbits that are on-average closer to the Sun to get ahead, and those on-average farther from the Sun to move more slowly. So, rather quickly, that initially horrible depth perception turns into a huge uncertainty in the predicted position in the sky.
No further observations of this asteroid have been made after July 5th. Today it is simply too faint to register on any but the largest and most powerful of telescopes on (or above) the Earth. If (or when) another successful observation is made, all potential orbits that don't agree with the new observation will be rejected, and the best-fit orbit will be refined. But at this point, we won't even be able to predict its next close approach of the Earth! When we see it again, it will be because we got lucky. We basically have to discover this space rock all over again.
So no, 2014 NZ64 is NOT a swarm of asteroids that will pummel us time and again over the next century - although this simulation may appear that way to the uneducated eye. These are just the possible predicted positions of a single asteroid as it moves along its orbit into the future. No wonder the JPL Impact Risk Table shows almost 400 possible collisions between the years 2017-2113! We really just have no idea where this asteroid is and where it's headed at this point.
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