So, about that asteroid

[unixronin]

It's by now been quite widely reported that NASA overlooked the possibility of asteroid Apophis interacting with a satellite in geosynchronous orbit, and was caought out by a German schoolboy who calculated there is actually a 1 in 450 chance that it will strike the Earth in 2036.  According to these stories, both NASA and ESA have acknowledged that the student is correct, and have corrected their calculations.

There's just one problem:  It's apparently not true.  NASA maintains that their numbers are correct, and that the chance of Apophis interacting with a geosynchronous satellite during its "close" pass in 2029 — let alone having its trajectory significantly altered — is remote.  The likelihood is that Apophis will pass between 32,000 and 38,000 km from the Earth at its closest approach, which is far too "high" to hit anything in low Earth orbit.  Yes, that's almost 10,000km inside geosynchronous orbit ... but Apophis will not approach in the plane of the ecliptic.  When it crosses the equatorial belt where almost all the geosynchronous satellites are, it's going to be about 51,000 km out — a good 10,000km beyond the Clarke orbits.  Even in the unlikely chance that it did somehow strike an errant geosynchronous satellite, we're talking 200 billion tons of iron and iridium here — even the largest satellites we have, like (say) a KH-12, would be like a mosquito hitting your car windshield.  No conceivable satellite impact could deflect Apophis enough to direct it into the "gravitational keyhole" that would put it at risk of striking the Earth in 2036.

In fact, not only is the part of the story about NASA and ESA acknowledging Nico Marquardt's numbers false, but, well, it turns out so is the part about Marquardt contacting NASA at all.  The appearances are that Bild — not so much "a major German newspaper" as "a major German tabloid" — made that part up to make the story sound better.

"NASA has never corresponded with this individual," NASA spokesman Duane Brown told CBC News. "We've spoken with [Near-Earth Object program manager] Don Yeomans, who came up with our current prediction for the asteroid, and he's sticking to his numbers."

But, just for the moment, let's assume Marquardt was right.  Let's suppose there really is a 1 in 450 chance of a collision in 2036.  Well, for starters, even that pales to near-insignificance beside the original estimate of 1 in 37 when Apophis was first plotted.  But let's ignore that for the moment.  Let's assume that the 1 in 450 — or the 1 in 45,000 — shot comes off, and Apophis hits the Earth in 2036 (or 2032, or 2029 ... it really doesn't matter which).  How bad will it be?

Well, we're talking about a thousand-meter ball of iron and iridium massing some 200 billion tons.  There's no doubt about it, we'd know we'd been hit.  But ... well, even at its original 1 in 37 chance, the highest Apophis ever got was a 4 on the Torino scale of impact risk.  What does a 4 on the Torino scale mean?  "A 1% or greater chance of collision capable of regional devastation."  It doesn't even make it into the "threatening" range.  Sure, Apophis is big ... but on the astronomical scale, it's really not that big.  It sounds bad if we say that it's 1/10 the estimated diameter of the Chicxulub impactor, and worse if we say that the Chicxulub impactor was a much less dense and more friable carbonaceous chondrite.  But really, how bad?

Remember that 1/10 of the diameter of the Chicxulub impactor means about 1/1000 of the volume.  Even though Apophis has a density close to 8 tons per cubic meter, that's only about two and a half times the estimated three tons per cubic meter of the Chicxulub impactor.  So we're talking about something that weighs about 400 times less.

But won't Apophis hit harder and penetrate more deeply, because it's a ball of iron and iridium, not a relatively fragile carbonaceous chondrite?

Well ... to put it succinctly, no.  At the 200 billion ton range, it really doesn't matter.  Which is heavier — a pound of feathers, or a pound of lead?  To even a chondrite of that mass, the atmosphere might as well just not be there.  But to even a nickel-iron or iron-iridium bolide of that mass, the Earth's crust is still awfully solid.  Yeah, we'd know we'd been hit ... but it's no dino-killer.  Even the worst-case scenario for Apophis (as shouted in near-hysterics by Yahoo News) is a major regional disaster, true — we're talking about a bolide roughly 40 times the size of the one that made Barringer Crater in Arizona — but it's no extinction-level event.

So right now, the best thing to do about Apophis is ... relax and have another beer.  (Or glass of wine, or cup of tea.  Whatever.)  It's really not worth worrying about right now.  Even if the stories were correct, it's not the Apocalypse.

And hey ... you just know someone will figure out a way to make a fortune mining all that iridium.  Imagine the possibilities if, by 2029 or 3023, we were in a technological position to be able to nudge Apophis into earth orbit.

Comments

[ilcylic.livejournal.com]

Yeah, through this whole story I was thinking about how much the price of steel has been going up lately... "200 billion tons! I bet that would bring the price of inch plate down!"

[ilcylic.livejournal.com]

So... How fast is this thing going? Like, if it's coming this close, and then rolling back out to the asteroid belt, can I catch a ride? On a more serious note, could we plant a colony on it, and seed the asteroid belt that way?

[ilcylic.livejournal.com]

Oh, apparently it only orbits between about .75 and 1.1 AU. No free ride to the belt for me.

[ilcylic.livejournal.com]

Actually, that might be better. We could set up a station there, and still get stuff back and forth every few years.

[unixronin.livejournal.com]

That's an interesting thought, using it as a transfer station.

[unixronin.livejournal.com]

Delivery'd be kind of a bitch though. :) But it'd mean we'd have all the steel we wanted for building stuff in orbit, and it wouldn't he too hard to punt the odd thousand tons or so into lunar transfer orbit now and then.

[ilcylic.livejournal.com]

I meant "if it hit". It's already down, all you have to do it mine it and refine it.

[unixronin.livejournal.com]

I think that comes under "delivery would be a bitch." :) But yeah, it would that .....

[http://users.livejournal.com/crossfire_/]

This whole Apophis thing has really irritated my Bad Science nerve, I can tell you.