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article imageIs Earth being hit by the wrong asteroids? Well, no, but there is a reason for that

By Paul Wallis     Aug 25, 2008 in Science
It could be embarrassing, being hit by the wrong sort of asteroids and not having a good statistical explanation. Seems that the vast majority of asteroids mostly aren’t made of the same stuff as the meteorites that hit Earth every day. What a relief.
Sounds like an interesting logical process, when studying things that have caused havoc on Earth for hundreds of millions of years, and wondering why the place gets hit by one sort not another. But it's produced some very useful science.
Actually, only about 8% of asteroids are made of the same material as the endless meteorites. The material is one of the reasons that asteroids are so standoffish. Most of them are affected by the Sun’s heat, and that in turn alters their course. This is called the Yarkovsky Effect.
Space Daily:
The Yarkovsky effect causes asteroids to change their orbits as a result of the way they absorb the sun's heat on one side and radiate it back later as they rotate around. This causes a slight imbalance that slowly, over time, alters the object's path. But the key thing is this: The effect acts much more strongly on the smallest objects, and only weakly on the larger ones.
"We think the Yarkovsky effect is so efficient for meter-size objects that it can operate on all regions of the asteroid belt," not just its inner edge, Binzel (MIT professor of planetary science Richard Binzel) says.
Thus, for chunks of rock from boulder-size on down -- the kinds of things that end up as typical meteorites -- the Yarkovsky effect plays a major role, moving them with ease from throughout the asteroid belt on to paths that can head toward Earth. For larger asteroids a kilometer or so across, the kind that we worry about as potential threats to the Earth, the effect is so weak it can only move them small amounts.
Near Earth Objects have been major science for a while now, and this might be a way of dealing with them. There are a lot of these things, and one of them, called Toutatis, seems to like our neighborhood.
It was thought possible to nuke incoming asteroids and deflect or destroy them, until someone figured out that was more likely to have asteroid shrapnel raining down on Earth than to actually stop the things.
Some of them aren’t solid, they’re more like traveling piles of gravel, big gravel, and giving them a reason to spray themselves all over the Solar System isn’t considered a good move.
So the Yarkovsky Effect might be an answer:
The new study is also good news for protecting the planet. One of the biggest problems in figuring out how to deal with an approaching asteroid, if and when one is discovered on a potential collision course, is that they are so varied. The best way of dealing with one kind might not work on another.
But now that this analysis has shown that the majority of near-Earth asteroids are of this specific type -- stony objects, rich in the mineral olivine and poor in iron -- it's possible to concentrate most planning on dealing with that kind of object, Binzel says.
"Odds are, an object we might have to deal with would be like an LL chondrite, and thanks to our samples in the laboratory, we can measure its properties in detail," he says. "It's the first step toward 'know thy enemy'."
Interesting to think that this is exactly the sort of space research that gets hit with budget cuts, when it gets to putting concepts into practice.
Well, even if “died of spreadsheet” isn’t much of an epitaph for humanity, at least people will know what hit them.
Eat your hearts out, dinosaurs.
More about Asteroids, Yarkovsky effect, Mit
 
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