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Fri February 15, 2013
David Nightingale: Asteroid DA14
The asteroid “DA14”, which will hurtle past us sometime after lunch today, was discovered by Spanish observers last year.
Our highest satellites, used for GPS, are just over 22,000 miles up, and DA14 will pass underneath that level – coming about 17,000 miles from us. Fortunately, NASA assures us we are safe.
Now Earth and Moon have been hit many times, over the eons, by asteroids.The explosive 1908 Tunguska asteroid, a similar size to the one passing us on Friday (which for a while many suspected might have been a mini-black hole) damaged 800 square miles of Siberia.
Asteroids, also called minor planets, orbit our sun in a belt between Mars and Jupiter, and there are thousands of them, but Friday's DA14 is not from that region. DA14 has a period and orbit similar to earth's -- actually 368 days. We haven't noticed the little asteroid because it's in a different plane from earth's orbit.
The first asteroid to be discovered was in 1801, by a Sicilian monk, and it was named Ceres, after the patron saint of Sicily. Ceres is big, as asteroids go -- about 300 miles across. By contrast, Friday's DA14 is only about the size of a 15 storey building. Interestingly, it was indeed in the approximate location predicted by Bode's law, between Mars and Jupiter.
Very occasionally asteroids collide. But,because there's really so much space between them, space craft, like Pioneers 10 and 11 on their way to Jupiter, have managed to pass through the asteroid belt without problems.
As mentioned, some asteroids are not in the asteroid belt at all.Icarus, for example, is in a highly elliptical orbit around the sun, and certainly goes closer to the sun than earth does. But again the commonality for asteroids is that they are bound to our solar system.
Asteroids are not usually named, but in 2004 asteroid Apophis caused some concern for a while. Last month, Apophis missed us by about a million miles (we are 93 million from the sun), but in 2029 it will return, much closer – roughly to the height of those GPS satellites. Worse, there were fears that its 2029 could possibly distort its orbit so that in 2036 it could conceivably come even closer.
I have 3 old newspaper clippings which I'm about to throw away, and they are: Jan. 2002, asteroid 2001 YB5 came to within roughly twice the distance to the moon... March 2002, an asteroid 165 feet across, coming from the direction of the sun but not seen until it was hurtling away, that got as close as moon distance... and June 2002, an asteroid the size of a soccer field that got as close as less than 1/3 of the distance to our the moon ...
Meteorites, by the way, might well be chips of asteroids, from those rare asteroid collisions. One of the most famous craters is in Arizona -- the Barringer Crater, from 25,000 years ago – which one can walk around and admire today.
From time to time people predict the world will come to an end, and 65 million years ago that almost happened. The dinosaurs became extinct at just about that time, and one theory is that the cause was a large asteroid in the Gulf of Mexico.
But while we can now – thanks to Newton – accurately calculate trajectories, and indeed the Smithsonian's Minor Planet Center does just that, and NASA runs a Near Earth Object Program, the ongoing problem for humanity is to detect them before they're upon us ...
Finally, a jarring thought is that today's asteroid was noticed as being in existence only 1 year ago.
Hats off to those Spanish astronomers!
Dr. David Nightingale is Professor Emeritus of Physics at the State University of New York at New Paltz, and is the co-author of the text, A Short Course in General Relativity.
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