Meet the asteroids

Are they gonna hurt us?

Will they obliterate the earth?

How are asteroids found?

Did asteroids deliver life?

What are they made of?

What about comets?

Asteroids in orbit

Searchin', searchin', gotta find a place to hide
As the threat of asteroid impact remains, the sad fact is that asteroids are hard to see. They reflect little light, and since they are always on the move, you must scan the same patch of sky over and over, looking for changing objects against the static background of stars. Some researchers are looking for light in the visible or infra-red bands. Others are using giant radar to bounce radio waves off the asteroids and read the return signal.

The LINEAR asteroid search observed this portion of sky last March. These are plots of the areas of the sky in which LINEAR performed asteroid search and follow-up observing during the indicated monthly lunar dark period. In each plot, each box represents a field that was searched for asteroids. Each field is revisited several times during the course of a night with a single image frame collected on each revisit. At the end of the night, the resulting frame set is processed to detect moving asteroids. Courtesy of the LINEAR project, MIT Lincoln Labs.

We won't get into the dispute about which approach is best, since each has advantages. But we will note that, according to the numbers, the most fruitful effort is run by the Lincoln Laboratory at the Massachusetts Institute for Technology. Using a 1-meter, satellite-tracking telescope that feeds data to a 1960 x 2560 pixel video detector, the Lincoln Near Earth Asteroid Research (LINEAR) can image a chunk of sky equal to almost 8 percent of the entire heavens.

Looking away from the sun, on moonless nights, in March 1998, LINEAR saw 151,035 objects, including 13 new near-Earth objects. The project sends data to the Minor Planet Center, a clearinghouse for information on these objects.

That's a gusher of data by any standard. But although the data on sky coverage indicate that LINEAR could view the entire sky in 12 nights, more asteroids and comets are constantly coming into view, and the telescope still cannot see faint but potentially destructive asteroids.

Thus if LINEAR and the other search projects are to reach the agreed goal of finding 90 percent of all significant potentially hazardous objects within 10 years, about 10 times as much effort is needed.

The ultimate goal of the NEAR Spacecraft mission is to rendezvous with and achieve orbit around the near Earth asteroid 433 Eros in January, 1999. Prior to its encounter with Eros NEAR flew within 1200 km of the C-class asteroid 253 Mathilde (right) on 27 June 1997. Courtesy of NASA. NEAR and asteroidDon't wanna live there, but a great place to visit!
Not content to observe asteroids with ever-more-sophisticated instruments from Earth, scientists have started visiting them. The benefits of such close encounters are clear in pictures made while the Galileo spacecraft was heading for Jupiter. Galileo made dynamite pics of asteroids Ida and 951 Gaspra. On 27 June, 1997, a fly-by by the Near Earth Asteroid Rendezvous produced lovely pictures of 253 Mathilde, a main-belt asteroid that's obviously been battered and bruised by a succession of heart-stopping impacts.

mathildeAll told, seven planned or operating missions expect to visit -- and in some cases return samples from -- 26 asteroids over the next 13 years.

A little knowledge: Dangerous?
Let's repeat that no known asteroid threatens Earth. But if an assassinating asteroid were found, what could we do about it? At least one simulation found that an impact with a house-sized piece of basalt would do little to change the course of a 1.7 kilometer asteroid. Given that nobody knows how to accelerate such a hunk of rock to asteroid-blasting speed anyway, we need alternatives. Some scientists suggest nudging another asteroid into an orbit that would deflect the attacker.

Is it just gloom-and-doom, or are there any honest-to-Pete scientific reasons to study asteroids?

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The Why Files
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