Thread: Science Science is Cool....
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Old 02-11-2013, 07:01 PM   #574
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Ohh yeah... by the way... There's a freakin 160' city-destroying asteroid whizzing toward the Earth right now. It will approach the atmosphere this weekend. But don't panic, Science is on top of it. It's calculated that there's no way it will hit us. Missing by a mere 17,000 miles.



Everything You Need to Know About This Friday’s Close Shave by Asteroid 2012 DA15
By Phil Plait | Posted Monday, Feb. 11, 2013, at 8:00 AM ET

On Friday, Feb. 15, the Earth is going to get a very close shave by an asteroid*. Called 2012 DA14, this 50 meter (160 foot) rock will pass just over 27,000 kilometers (17,000 miles) from the Earth’s surface. This is closer than our geosynchronous satellites, so this really is a close pass!

But, to be very clear: This asteroid poses no threat to us right now, nor in the foreseeable future. Friday’s miss is just that: a miss. And, in fact, this is a good thing, since any time an asteroid gets close (but misses), we learn a lot, including how to find them, how to track them, and even how to talk about them to the public.

So let me tell you all about this little rock, and why it’s so cool.

2012 DA14 was discovered in February 2012 by astronomers at the Observatorio Astronómico de La Sagra; it passed the Earth on Feb. 16th of that year, missing us by a comfortable 2.6 million km (1.6 million miles). The asteroid has a very Earth-like orbit, talking 366 days to orbit the Sun. Its orbit is slightly more elliptical than ours and tilted by about 11° to ours as well. All that’s about to change though: After the encounter this year, the Earth’s gravity will change the orbit of DA14 quite a bit, reducing the period to about 317 days.

Asteroids fall into various classes depending on their orbits; Apollo asteroids, for example, have a semi-major axis (the radius of their orbit measured across the long part of the ellipse) greater than Earth’s, and Atens have semi-major axes smaller than Earth’s. Right now, DA14 is an Apollo, but after the 15th its orbit will change shape so much it will become an Aten.

The exact shape of its orbit after this weekend’s event isn’t known, but we do know it well enough to rule out any potential impact for quite some time; the next encounter won’t be until 2046, and even then it won’t get closer than about 1.6 million km (1 million miles).

How Close a Miss Is This?

DA14 will slip past at a distance of 27,000 kilometers from the Earth’s surface. The Earth itself is about 13,000 km across, so the asteroid will be twice our own diameter away.

So, Can I See It?

Even though it’s passing pretty close, DA14 is so small that it never gets bright enough to see with the unaided eye. I’ve seen predictions that it will get to about magnitude 7, which is less than half as bright as the faintest thing you can see. However, that’s well within range of binoculars or a small telescope.

So It Won’t Hit. But What If It Did?

Ah, you’re one of those people who enjoys scaring the crap out of yourself. OK, let’s think about what would happen if DA14’s path actually did intersect ours.

We have some decent comparisons. There is a crater in Arizona called, oddly enough, Meteor Crater, that’s about 1.2 kilometers (0.75 miles) across. It was created 50,000 years ago or so by an asteroid roughly the size of DA14, which upon impact probably detonated with an explosion equivalent to a 20 megaton nuclear weapon going off.

That asteroid was metallic, so it could make it through the Earth’s atmosphere and hit the ground. We now know many asteroids are much less sturdy, and probably would explode high in the atmosphere, disintegrating under the excruciating pressures of screaming through the air at Mach 20. That happened in Siberia in 1908 in the famous Tunguska event. Again, a DA14-sized rock came in, but this time blew up high over the Earth’s surface.

Not that this was any blessing. Trees were knocked down and set aflame for hundreds of square kilometers, and anyone within probably 10 kilometers wouldn’t have lived to tell the tale.

So we really don’t want rocks like this hitting us. They won’t cause a global extinction, but it doesn’t take something ten kilometers across (like the one that did in the dinosaurs) to have a catastrophic effect. Anything the size of DA14 would be able to take out a city. And it doesn’t even have to hit over populated land; just having one come in over the United States could trigger a global economic collapse. Remember, it only took a handful of people flying a couple of planes into buildings to do that. An asteroid impact, especially one that comes in without warning, could be a lot worse.

This threat is no joke. It’s quite real, and we need to take it seriously. We need more observatories watching the sky, and a plan in place in case we do see one with our number on it. Some new observatories will soon be coming online that will help. Also, both NASA and the privately-funded B612 Foundation have plans to launch space missions that can better look for near-Earth asteroids. B612 even has ideas on how to stop a potential impactor from ruining our day, too. I gave a TEDx talk on this very topic.

By the way, the asteroid Apophis made a lot of headlines when it was thought to have a non-zero chance of whacking us. That has now been downgraded to zero, so we’re safe from that one, too.

OK, Fine. But Can It Hit a Satellite?

Since DA14 is passing closer than some satellites, it makes sense to ask if it will hit any. The answer is that it almost certainly won't. There's a tiny chance, but the rock is small, and satellites smaller. Space, however, is big. That's why we call it space. There are billions of cubic kilometers of emptiness out there, only very slightly occupied by solid bits of matter.

Put it this way: Hits to satellites by tiny grains of cosmic debris are incredibly rare, and there is a lot of that stuff floating around out there. The odds of one lone chunk of rock hitting a satellite are far, far smaller. I'd bet a lot of money nothing will get hit by DA14—and of course, satellite manufacturers actually are betting that money. NASA has consulted with satellite comapnies and given them updated coordinates of DA14 as a precautionary measure, but I don't think anyone seriously thinks there's any real danger to our birds out there.

What, Me Worry?

For most people, this pass of 2012 DA14 is a non-event; if you hadn’t hard about it you would never have known it would happen. It will pass us in the night, silent and dim.

But this is in fact a big deal. For one thing, it allows us to check our models of asteroid behavior; how accurate were predictions last year based on observations of the time, how well can we improve them, how quickly and accurately are new observations included? These can all be checked.

Plus, this sucker will be moving across the sky fast. At closest approach it will appear to move in the sky quickly enough to cross the face of the Moon in about 40 seconds. Getting most telescopes to track that fast is not all that easy. It’ll be a nice test of engineering.

Also, we’ll have a lot of observations of it, and those will have to be processed and compiled into a set of orbital parameters used to make predictions in the future. I imagine that will keep some astronomers busy for a while.

And let’s face it, people will have heard of this, one way or another. It’s not hard to find breathless headlines (one I saw said the asteroid will pass “perilously close” to Earth, a phrase that has no meaning except to scare people; a miss is a miss) and ridiculous conspiracy theories that the asteroid will actually hit or affect us in some way. We’ve seen those before—and they’ve always been wrong—and we’ll see them again.

So for me, this asteroid is interesting scientifically, but it’s also yet another exercise in informing the public, who are curious about scientific matters in general and in asteroids specifically. I’m actually pretty happy with what I’m seeing out here right now; lots of facts and not as much nonsense and scare-mongering as usual. Maybe we’re doing better.

And plus, let’s face it: This near miss of an asteroid is simply cool. It’s a big Universe out there, and the Earth is a teeny tiny target. We don’t get an opportunity like this very often, and I think it’s wonderful it’s getting the attention it is. Everything happening with DA14 is a net positive, including the public awareness. I hope that as these passes continue to happen people become even more excited by them, and it leads to us being able to fund more work on understanding asteroids, from observing them to actually visiting them some day.
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