The Truth About Close-Passing Asteroid Apophis



Asteroid Apophis is back in the news, this time due to the release of a report by Russian scientists, which the Huffington Post chose to present in pairing with a scary, factually incorrect and very misleading video.

We asked Don Yeomans for comment. He is manager of NASA’s Near Earth Object Program. His comment was:

The Huffington Post video is creepy and all wrong.

Asteroid Apophis will get to within 0.1 AU of Earth in January of the year 2013. In late 2012 and early 2013, Apophis will be observable using both optical and radar equipment. That will be a very exciting time for astronomers, and for the rest of us! Apophis is expected to be visible to the eye alone in the night skies of Europe, Africa, and western Asia, a first for an asteroid in recorded history (as far as we know). Yeomans said:

In fact it will get beneath the geosynchronous satellites [which are 22,000 miles up], the same satellites that are probably used to beam your radio signals to your listeners. So that’s kind of exciting. But it won’t hit the Earth.

The data collected in late 2012 and early 2013 — just two years from now — are expected to make possible a significant improvement in our understanding of the orbit of Apophis and remove any possibility for an Earth impact on April 13, 2036. Or, as David Helfand of Columbia said when EarthSky interviewed him in 2010 on killer asteroids, the risk from Apophis is “essentially zero.”


Gratuitous and wholly imaginary asteroid Apophis collision pic. Not likely!

So Apophis is more a curiosity than a threat, at this point. As things stand today, ignoring the new orbit calculations two years from now (which might change everything I say next), astronomers speak of a “keyhole” through which Apophis would have to pass in 2029, at another sweep past Earth, in order to be on a collision course with Earth in 2036. According to Dr. Yeomans:

If the object passes through a 600-meter-sized keyhole in 2029 — that is, a location in space that is only 600 meters wide — it will indeed hit the Earth in 2036. But the chances of its actually passing through this 600-meter-sized keyhole in space in 2029 are extremely low.

Before the improvements in our knowledge of Apophis’ orbit that are sure to come two years from now, the probability of an Apophis impact with Earth in 2036 is 1 to 233,000. While greater than your chance of winning a lottery (many millions to one), it’s still very very unlikely. What’s more, the probability is likely to go to zero after the 2012-2013 observations are made, Dr. Yeomans said.

He also said that, in the very remote case where the impact probability does not go to zero as 2036 approaches — if the asteroid does seem that it will come too close for comfort — there still would be time to send spacecraft to Apophis and deflect away from Earth. In fast, astronomers have been meeting periodically since the 1990s on ways to deflect asteroids, should they come too close. The ways include sending nuclear weapons to explode on them or near them — putting up a satellite that gravitationally tugs at the asteroid a little bit, so its orbit changes ever so slightly just enough to miss the Earth — or outfitting the asteroid with a mass driver that would eject material from the asteroid into space, decreasing its mass and thereby changing its orbit. There are more asteroid collision avoidance strategies ideas, which you can read about on Wikipedia. So people are, indeed, contemplating the physics and engineering challenges of keeping us safe from asteroid collisions.

Apophis, by the way, is about 300 meters wide. That’s about a thousand feet wide or, as HuffPo said in an update posted after its Feb. 9 posting of the inappropriately scary video: merely a bit larger than two football fields. In other words, the asteroid depicted in the HuffPo video is not comparable to Apophis.

Yeomans concluded:


Some Russian scientists, who should know better, are raising unnecessary red flags over the 2036 Apophis case. I suspect that is why there is renewed current interest in Apophis.

Enough said for now. Asteroid Apophis is not on a sure collision course with Earth in 2036, astronomers do have their eyes on this object and — if a too-close pass seems imminent — we’ll have plenty of time for a deflection via spacecraft. Okay? Now, stop worrying and enjoy the weekend.

[Image by ESO]

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