David Braun reports in the National Geographic News that scientists have identified a thousand-yard-wide asteroid that may be heading for a collision with Earth 878 years from now.
Using radar and optical measurements made over the past 51 years, researchers have calculated that there is up to a one-in-300 possibility that Asteroid 1950 DA will slam into the Earth on March 16, 2880. ?We calculated the probability of collision based on what we know about the physical aspects of the asteroid and many other factors,? says Jon Giorgini of NASA?s Jet Propulsion Laboratory at the California Institute of Technology in Pasadena. ?As we get more information we will be able to adjust the level of probability up or down.?
Odds of one in 300 is the highest Earth-impact potential ever assigned by scientists to an object in space, according to Giorgini. The consequences of a collision from an asteroid a thousand yards in diameter are unknown. A direct hit could possibly destroy an entire city and an ocean impact could create a massive tsunami capable of drowning nearby coastal areas. ?Nothing good can come from such an impact,? says Giorgini.
One of the easiest ways to deflect the asteroid past Earth would be to alter its surface, changing the amount of heat energy it radiates, says Joseph Spitale, a research associate in planetary science at the University of Arizona. That would have the effect of subtly altering the way the asteroid moves, causing its path to change.
Spitale says the Yarkovsky Effect, which uses heat radiation, could be used to make an asteroid drift off its path. ?The thermal emission from an asteroid acts like a rocket force in the opposite direction, although it is really, really weak,? Spitale says. ?If we can somehow change the thermal radiation being emitted by an asteroid, we can affect the object's orbit. A tiny thrust acting over a long time can be enough to nudge an asteroid from a path heading towards the Earth to one that narrowly misses the Earth.?
The Yarkovsky Effect is completely determined by temperatures on the surface of the asteroid, so it can be manipulated if the surface can be altered in a way that changes that temperature distribution. Asteroid DA 1950 ?looks like a good candidate to test the Yarkovsky Effect,? Spitale says. ?We have a really long base line in time and we are able to predict its orbit over that time.?
To use the Yarkovsky Effect would require doing something on Earth to change the asteroid?s surface temperatures. ?I think people will come up with all sorts of creative ideas about that,? Spitale says. ?For example, if we could cover the surface of the asteroid with half an inch of dirt, that would plausibly be enough to change the Yarkovsky Effect quite a bit. Of course, that's a lot of dirt and it would probably require a couple of hundred rockets to get it all up there. It would be really expensive.?
Another possible solution, Spitale says, would be to ?paint? the asteroid?s surface white. ?That would make a big change to the way the object reflects sunlight. That might require a thickness of less than a 20th of an inch over the entire surface,? he says.
A third solution would use conventional explosives to break up the asteroid into smaller pieces. One rocket might be enough to complete the job, and getting it there would certainly be possible using current space technology.
The last approach would be the cheapest solution, Spitale says. ?Unfortunately, you would probably lose most of the debris to space. However, this approach might alter the character of the surface in some other useful way.? How we can deflect DA 1950 away from the Earth depends on the exact physical nature of the asteroid.
Giorgini says, ?We won?t know for sure whether this asteroid is on a collision course until we can determine which way its north pole is pointing.? Current calculations are based on all the possibilities, and the outcome of these scenarios range from zero to.33 percent probability that the asteroid will hit the Earth.
This is the first time so many factors have been taken into account when predicting an asteroid?s orbit. Giorgini and the other researchers have looked at not only the asteroid itself but also at such things as the gravitational influence of other asteroids, the shape of the sun, and the effect of solar wind.
Until now, DA 1950 had been seen only twice?once in 1950 and again on December 31, 2000. Although the asteroid orbits the sun once every 2.2 years, its orbit comes close to the Earth only about once in every 51 years. It can be seen visually through telescopes as a moving point of light. Only through radar, however, can scientists determine the nature of its surface and how it spins. Because the asteroid needs to be fairly close to Earth for radar to be effective, opportunities to study it are rare.
The next time scientists will be able to use radar to study the asteroid will be in 2032. But astronomers will get an optical view of the asteroid in about five or six years, and may be able to learn more about its physical aspects.
?We need to know how it spins, its mass, its exact shape, and the patterns of darkness and lightness on its surface,? Giorgini says. ?If we can?t get this information from our telescopes, then the only way to do it will be to send a spacecraft to go and take a look at it.?
To learn about what?s out there that we need to be aware of, read ?Dark Matter, Missing Planets & New Comets? by Tom van Flandern,click here.
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There may be more asteroids in our solar system than previously thought, according to the first infrared asteroid search The European Space Agency?s Infrared Space Observatory (ISO). The Deep Asteroid Search project indicates that there are between 1.1 million and 1.9 million space rocks in the main asteroid belt, about twice as many as previously believed.
Despite being in our own Solar System, asteroids can be more difficult to study than very distant galaxies. The brightness of these rocky objects varies considerably from minute to minute. They move very quickly with respect to the stars and often appear as trails on long exposure images. Their elusiveness explains why their actual number and size distribution remains uncertain. Most of the almost 40,000 asteroids catalogued so far orbit the Sun, forming the main asteroid belt between Mars and Jupiter, too far away to be a threat to Earth.
However, astronomers keep a closer eye on another category of asteroids, the Near Earth Asteroids (NEAs), which have orbits that cross, or are likely to cross, Earth?s orbit.
Astronomers Edward Tedesco and Fran
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