Space Rock Just Misses The Earth

[Zac Naloen]

http://news.bbc.co.uk/1/hi/sci/tech/7921279.stm

Space rock makes close approach
An asteroid which may be as big as a ten-storey building has passed close by the Earth, astronomers say.

The object, known as 2009 DD45, thought to be 21-47m (68-152ft) across, raced by our planet at 1344 GMT on Monday.

The gap was just 72,000 km (44,750 miles); a fifth of the distance between our planet and the Moon.

It is in the same size range as a rock which exploded over Siberia in 1908 with the force of 1,000 atomic bombs.

The object was first reported on Saturday by the Siding Spring Survey, a near-Earth object search programme in Australia.

It was confirmed by the International Astronomical Union's Minor Planet Centre (MPC), which catalogues Solar System objects.

The closest recent flyby listed by the MPC is 2004 FU162, a small asteroid about 6m (20ft) across which came within about 6,500km (4,000 miles) of our planet in March 2004.

The latest object, 2009 DD45, passed by our planet at only twice the altitude of satellites in geosynchronous orbit.

In 1908, an object with a similar size exploded over Siberia, flattening 80 million trees over an area of 2,000 square km (800 square miles) near the Tunguska river.

"There is still a lot of debate over how big the Tunguska object was," Professor Alan Fitzsimmons, an astronomer at Queens University Belfast, told BBC News.

"It was always thought to be 50 or 70m across. But some recent calculations have implied it may have been even smaller than that - maybe down to 30m in size. There's a large uncertainty there, but it puts (this object) in the same ballpark."

Christ, just imagine if that had been a few degree's different and managed to hit a populated area

[Kanastrous]

The *really* disturbing part is that it wasn't detected until Saturday.

For all practical purposes that's no warning.

[Zac Naloen]

Just imagine how the public would react if this did hit


"Why didn't you warn us!"

The only practical response would be... "What would you have done?"

[Solauren]

Better response:

You don't want us funding space stuff, so we had no way to detect it!

[Kanastrous]

"What would you have done?"

Lie down. Put paper bags over our heads.

Christ, just imagine if that had been a few degree's different and managed to hit a populated area

A open ocean impact probably would have sucked, too. That looks like enough energy to drive a tsunami with the potential to wreck several populated areas.

[The Duchess of Zeon]

And this is why we should pay the Russians to build a couple of super-stretched Energias with eight boosters to stand ready on the pad with 6 gigaton thermonukes (which after all are quite theoretically possible--the only question is if we can make one that weighs less than 100 tonnes, I suppose). They'd do quite well against impactors of that size (or even substantially larger--only really big objects that even a huge, high-end theoretical thermonuke would only fragment rather than disintegrate down to sizes sufficient to all burn up in the atmosphere would genuinely require advanced detection for us to stop), and we'd only need a few hours warning. Also it would be cool, but I digress.

[Darth Wong]

Better response:

You don't want us funding space stuff, so we had no way to detect it!

The public never takes responsibility for its own short-sightedness. They pressure politicians to cut spending on anything that doesn't give them immediate personal benefit, then they get angry when this short-sightedness (which they invariably blame on the politicians for capitulating to their own demands) comes back to bite them in the ass.

[Kanastrous]

Maybe big deadly space rocks were conceived with the intent of weeding out species like us.

Makes you think.

What are the most likely reasons this rock escaped earlier notice, anyway? Not enough people looking? Not looking in the right direction? Not looking with the right instruments?

[Darth Wong]

A open ocean impact probably would have sucked, too. That looks like enough energy to drive a tsunami with the potential to wreck several populated areas.

Upon what basis do you say it looks like enough energy to create a large tsunami? Did you perform any calculations?

This peanut-shaped 21 to 47 metre wide asteroid would only be maybe ~16000 m³ (estimating by using a 21 metre wide 47 metre long cylinder), so even if its composition were nickel-iron with a bulk density of ~8000 kg/m³, its mass would be what, maybe 130,000 tons? If it's moving at 30 km/s, that's around 6E16 J, or ~14 megatons of KE, some of which would be dissipated with air friction before it even hits the ground.

That's a pretty big boom, but that's not going to splash down in the ocean and create a tsunami.

[The Spartan]

By means of comparison, the 2004 Tsunami was caused by a earthquake that release, IIRC, around 475 megatons.

[Darth Wong]

Addendum: a 1 m² footprint column of air reaching up into space would have a mass of roughly 10 tons, hence it exerts roughly (1E4 kg)(10 m/s²)=1E5 N of downward force, thus producing the atmospheric pressure of ~100 kPa. Ergo, if this asteroid hits the atmosphere and flips over into an end-on configuration, its cross-sectional area will be πr² ~= 350 m², so the mass of the air column ahead of it will be roughly 3500 tons. That's more than 20% of the mass of the asteroid (based on an assumption of high asteroid density), so it should significantly slow down and degrade the rock before impact. If the asteroid is composed of a lower-density material, it might be mostly destroyed before impact.

[Forum Troll]

What are the most likely reasons this rock escaped earlier notice, anyway? Not enough people looking? Not looking in the right direction? Not looking with the right instruments?

Not much looking, basically. We spend under a millionth of our economic resources looking, like $3 or $4 million a year as a footnote within NASA's activities plus some other small efforts internationally. Sometimes NEOs are just detected by amateur astronomers. Still, even so, over the past decade most of the big ones above 1-kilometer size appear to have been found, though there are hundreds of times as many objects still above 100 meters diameter and in the 100 megaton impact range or above.

[Darth Wong]

I should note that I'm using some rather paranoid assumptions to get that 14 megaton figure: an asteroid moving at 30 km/s rather than 15 km/s, being composed entirely of nickel-iron, and disregarding atmospheric drag despite the fact that the air column is >20% of the mass of the asteroid itself. Many studies project that asteroids below 50m in diameter won't even reach the surface at all.

[Kitsune]

How frequent do rocks of this magnitude pass within say 100,000 km of earth...Is it an every few year event if anyone knows?

[Darth Wong]

How frequent do rocks of this magnitude pass within say 100,000 km of earth...Is it an every few year event if anyone knows?

It's been estimated that we get hit with a Hiroshima-level asteroid every year or so, but nobody notices because the asteroid is destroyed in the atmosphere at high altitude. I do have a chart from my "Hazards of Asteroids" book, but it would take a while to transcribe. Timeframes are more in the range of centuries to millennia for larger impacts capable of destroying cities or creating tsunamis.

[starslayer]

This asteroid wasn't detected until a few days ago mostly because it's so tiny. This makes it extremely faint, and a very tough target to pick out. Add to that the fact that not many people are looking, and even if there were more, the sky is still an enormous place, and is now replete with our own debris and satellites (which take time to identify and then ignore), and it's no wonder that no one saw this coming.

For comparison, the Tunguska asteroid is believed to have been about this size, perhaps a little bigger. So while it would make it low enough to do quite a bit of damage to a populated area, it would only hit the ground were it nickel-iron, and perhaps not even then. A stony asteroid that size will definitely break up in the air, IIRC with about as much energy as Mike calculated (there are a range of estimates*). Even so, populated areas take up an extremely small portion of Earth's total surface area, even when compared to total land surface area.

And this is why we should pay the Russians to build a couple of super-stretched Energias with eight boosters to stand ready on the pad with 6 gigaton thermonukes (which after all are quite theoretically possible--the only question is if we can make one that weighs less than 100 tonnes, I suppose). They'd do quite well against impactors of that size (or even substantially larger--only really big objects that even a huge, high-end theoretical thermonuke would only fragment rather than disintegrate down to sizes sufficient to all burn up in the atmosphere would genuinely require advanced detection for us to stop), and we'd only need a few hours warning. Also it would be cool, but I digress.

Which launch site in Russia do you propose to use so as to avoid the problem of bad weather making it impossible to launch? I suppose a better first question to that is: how bad must the weather/conditions be to prevent a launch on such short notice, especially with such a large and relatively fragile assembly?

*Including one from Toon, presumably of nuclear winter fame, of a 670 MT blast at Tunguska. I took this guy seriously in the recent nuclear winter thread why exactly?

[Edi]

By means of comparison, the 2004 Tsunami was caused by a earthquake that release, IIRC, around 475 megatons.

The 2004 tsunami also had other factors working on it that would be absent in an asteroid impact. It was caused by a tectonic plate fault shifting upwards by several meters, thus shoving all the water above it upwards by that same amount and the tsunami resulted from the ripple of all that mass of water settling back down and equalizing as it sort of "fell" to the sides to do so. That's the real reason that tsunami was so devastating, it was due to the mechanics of that particular earthquake.

Think of small levers moving big rocks.

An asteroid impact would have different factors such as what DW already posted and to get a cross section similar to the area of the 2004 fault, it would need to be kilometers in size. A small rock like this one would at best cause a high altitude explosion and even if it did reach the ocean, it would only make a big splash. Now, if it was one of those kilometer(s) sized thingys, that's a different ball game.

[Traveller]

Look, the only reason it missed is because the American Guv'mt, went and recruited a bunch of rowdy, ill-disciplined, barely literate roughnecks, flew them to NASA's super-secret training facilty(buried deep below the EPCOT center), and trained them in the art of asteriod deflection. They were led by a grizzled hard-drinking, plain spoken veteran roughneck, who lists 'Shooting golf balls at pinko-commie enviromentalists' off his private off-shore oil platform as one of his favorite pasttimes. NASA defended the decision to send the crew of misfits as opposed to...well... actual astronauts, saying "These guys are a lot more rowdy and colorful than anyone at NASA and the average american can more readily identify with them so for us it was a win\win". The mission however, did not come without a cost, for no explicable reason, both the ISS and one of the two shuttles sent out were completely destroyed. Also the Big rowdy roughneck who despite his large size and gruff demenor, was really a big teddy bear, died when he heroically volunteered to stay to behind and mannually detonate the nuke after, for some inexplicble reason, its arming mechanism
malfunctioned*. You see Nothing at all to worry about.

One a related note, as part of President Obama's economic stimulus packages 'Buy American' clause, all the nuclear weapons used in this effort, were 100% built with pride in the US of A.

[The Spartan]

*snip explanation*

Oh, don't misunderstand, I'm not suggesting that it's a direct comparison. I'm only using that as a reference compared to a 14 Mt release.

That said, you're right in that the water in the case of an impact would absorb much of the impact and that amount actually displaced would be significantly less. For a very rough comparison, drop a 25 pound dumbbell in a lake and then put your arm underneath the water and force the water upward, you should get a much bigger displacement.

[PeZook]

It wouldn't cause much damage if it hit the ocean, but 14 megatonnes dispersing in the atmosphere as thermal energy would still be a spectacular sight to watch.

...from a safe distance, of course.

[wautd]

The *really* disturbing part is that it wasn't detected until Saturday.

For all practical purposes that's no warning.

I mentioned this story at my parents during dinner this evening. My father actually said something in the lines of "I don't care about this kind of news and at least they could detect it". Offcourse, he shut up when I said that they only detected it a few days ago.

Would we been able to stop it if we had detected it sooner by the way? It doesn't seem like an easy task.

[CaptainChewbacca]

If we had detected it sooner AND it was determined to be on a collision course? Maybe. Its probably small enough we could have tried to crack it into smaller bits with a nuclear missile, but there's a very good chance we would have missed.

[Mayabird]

Even if we can't blow the thing up, with a little warning we could at least try to evacuate any areas that might be hit (or let the people around know that it's going to suck for a while) if a land strike or warn ships away from a sea strike.

[Forum Troll]

Would we been able to stop it if we had detected it sooner by the way? It doesn't seem like an easy task.

Depends how much sooner you have warning.

While hitting an object like this when it was still a ways out is technically possible, there's definitely no "Standard Long-Range Space Interceptor Guidance Package" just available off-the-shelf. For example, the guidance systems on ICBMs are just made to guide them to a particular ground location, not hit a moving space target, and they don't have the velocity capability for more than their normal suborbital mission (or maybe LEO if a lower payload).

However, if you had detected it on a prior orbit instead or if you otherwise had months of warning, a satellite booster like one of those used for deploying satellites as high as GEO could be modified, and a suitable guidance package could be rigged up. NASA has sent space probes right up to comets and asteroids before.

A lightweight sub-megaton yield nuke might suffice for a rock this relatively small, not vaporizing it, but, if sufficient yield relative to target size, disintegrating it while it was thousands of miles out, into so many tiny pieces than no surviving pieces would do anything more than fireworks in the upper atmosphere.

Whether you even bothered might depend on modeling of its trajectory, its impact location and effects. You wouldn't need to worry about an asteroid of this size if it happened to be just headed for an uninhabited area of ocean.

[starslayer]

Whether you even bothered might depend on modeling of its trajectory, its impact location and effects. You wouldn't need to worry about an asteroid of this size if it happened to be just headed for an uninhabited area of ocean.

The uncertainties in tracking orbits are so large that most of the time we can't even really be sure if it will even hit Earth rather than just fly past until we've gathered plenty of data. It would probably take several weeks of data to really get a handle on just where the damn thing was going, to say nothing of a possible impact site. For example, in the recent satellite collision, everyone thought that they'd probably miss, and those things had been in LEO for years. A rock like this that comes comparatively out of the blue wouldn't be easy to pin down.