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Space object has
1-in-500 chance
of hitting Earth,
scientists say

Up to 230 feet long, it could
be an asteroid or just junk,
UH scientists say

---

By Helen Altonn
Star-Bulletin

University of Hawaii planetary astronomers have discovered an asteroid-like object with a 1-in-500 chance of hitting the Earth in 30 years, according to NASA's Jet Propulsion Laboratory.

David J. Tholen and Robert J. Whiteley detected Object 2000 SG344 on Sept. 29 with the 88-inch Canada-France-Hawaii telescope on Mauna Kea.

A Technical Review Team of the International Astronomical Union said it could be a small asteroid -- or a piece of space junk.

The team verified computations by a group of international experts suggesting the object has a remote chance of striking the Earth in 2030.

However, the team said, "The greatest likelihood is that future observations of the object will yield higher precision orbit computations that will show with certainty that it will miss the Earth entirely."

The UH astronomers have found about a dozen asteroids while searching for a particular type known as Aten, the name of an Egyptian god, Whiteley said. "This new guy is a member of the Aten class."

Whiteley earned a doctorate degree at the Hawaii Institute for Astronomy and left about six weeks ago for the University of Arizona, where he's a postdoctoral researcher.

He returned for observations in September and will continue working with Tholen, who is internationally recognized for his work in characterizing asteroids.

Whiteley said they're getting new information from pre-discovery observations where Object 2000 SG344 wasn't recognized.

"We've been pounding at this all day," he said by telephone yesterday from Tucson, explaining the additional data has strengthened the findings.

"We haven't seen a stable impact probability that's this high. One-in-500 is not a huge chance, but it's more than we've ever seen before."

The Technical Review Team said the object's unusual Earth-like orbit suggests it might be a man-made rocket booster from the Apollo era. It could be a left-over space probe or rocket stage.

If it is a man-made object, Whiteley said it most likely is from a third-stage Apollo rocket.

But he believes it's an asteroid because of its medium size, about 98 to 230 feet long. There are more asteroids of that size than space junk, he said, noting that Apollo third stages were quite large.

Donald Yeomans, manager of the Near-Earth Object Program Office at the Jet Propulsion Laboratory, said if it is an asteroid and it hits Earth, "it would be equivalent to a fairly sizable nuclear blast."

It could hurtle more than 23,000 tons of rock through the atmosphere in a blast of 15 to 20 megatons.

For now, that is "fairly low in terms of concern," Yeomans said.

"It's not planet-busting by any means," Whiteley said. "Blasts of this size have been seen on the Earth's surface before. We've made them. But they're powerful, and we don't know where they're (asteroids) going to land."

The review team said Object 2000 SG344 seems too bright to be an Apollo rocket booster, but it's not ruling out that possibility.

Although the object's size was estimated on the basis of its brightness, Whiteley said no one was able to measure its brightness before it faded.

He said the object has a "really complicated orbit. We've been playing with the orbit all day, and it's a big mess. It's fascinating, but a very, very complex approach to Earth. It's a very Earth-like orbit, which is why it makes so many close approaches."

Orbital calculations last month by Andrea Milani of the University of Pisa, Italy, first indicated the possibility of a future impact.

Paul Chodas at the Jet Propulsion Laboratory estimated a one-in-500 chance of the object hitting Earth on Sept. 21, 2030.

He said there's a 1,000-times greater chance of it colliding with the Earth than any asteroid-like object yet discovered. But by present estimates, it's expected to miss the planet by 15 times the distance between the Earth and moon.

Scientists are uncertain about the precise orbit, however, and can't rule out a possible collision. If it's a small man-made booster, it would be lightweight and pose no danger to Earth, they said.

"It is interesting to note the chance of object 2000 SG344 striking the Earth in 2030 is actually somewhat less than the chance of an undiscovered object of the same size striking the Earth in any given year," the review team said.

"Thus, object 2000 SG344 is more interesting than threatening, but the international efforts to characterize the nature and future motion of this object will continue."

The object was last near Earth in 1971, when it was about 8.4 million miles away.

It won't return for nearly 30 years because it moves a little faster than the Earth around the Sun and is slowly drifting away.

Many encounters might be possible after 2030 because the Earth's movements could change its orbital period, the scientists said. "The likelihood of this situation is also under study."