James V. Scotti
(Editors note: Scotti is observing on Spacewatch. He will be back on campus
Friday, July 23.)
TUCSON, Ariz. -- A unique near-Earth asteroid discovered last year by
Spacewatch at the Univerity of Arizona in Tucson is the fastest-spinning
solar system object yet found, scientists report in tomorrow_s issue (July
23) of Science.
Only 30 meters (100 feet) across, asteroid 1998 KY26 spins once every 10.7
minutes. That_s 10 times faster than the spin rate of any other object and
almost 60 times faster than the average of all known asteroid rotation
periods, the scientists say.
Whirling at that speed and given its size, 1998 KY26 has to be a strong,
single chunk of rock that was sent reeling from its parent asteroid in some
space collision, said James V. Scotti , a senior research specialist at the
UA Lunar and Planetary Laboratory (LPL) and a co-author of the Science
LPL Professor Tom Gehrels, Spacewatch co-founder, discovered asteroid 1998
KY26 on May 28, 1998, using the 0.9 meter (36-inch) Spacewatch telescope at
Kitt Peak, Ariz. Six nights later Scotti, joined at the Spacewatch
telescope by Dan Durda, took 111 images of the asteroid, measuring its
minimum to maximum changes in brightness. Durda of the Southwest Research
Institute in Boulder, Co., was formerly with LPL.
Astronomers at telescopes in the Czech Republic, Hawaii and California also
made the same kind of photometric measurements from June 2 to 8. This was
when the asteroid made its closest swing by Earth at a half million miles,
or twice the distance between the Earth and the moon. Between June 6 and 8,
Steven J. Ostro headed a team from the NASA Jet Propulsion Laboratory in
Pasadena, Calif., that used the Goldstone X- band radar of NASA_s Deep
Space Network to track the asteroid. Radar echoes revealed the asteroid_s
rapid spin rate. Petr Pravec of Ondrejov Astronomy Institute in the Czech
Republic combined data gathered by the different optical observing groups
and constructed a light curve to determine the precise rotation rate.
The astronomers discovered the size and shape of 1998 KY26 from the radar
echoes. This asteroid is unusual in that it is almost spherical, with a
bare-rock surface pocked at least in part by meteoroid bombardment, they
report. Their optical and radar observations show this asteroid is similar
to carbonaceous chondritic meteorites, objects that formed early in solar
system history. These meteorites are rich in primordial complex organic
compounds and water.
Asteroids in the 30-meter-diameter range survive between 10 million and 100
million years before being destroyed in space collisions. Carbonaceous
chondrites are weaker meteorites, so this asteroid will be smashed sooner
than later, they add.
Information from recent asteroid flybys suggests that large asteroids are
less dense than the meteorites recovered and measured on Earth. Scientists
theorize that most larger asteroids are porous "rubble piles" rather than
monolithic bodies, Scotti said. Current theory says that "these rubble
piles are conglomerates of debris broken apart by multiple collisions and
held together by their mutual gravity, spinning slowly enough so that they
don_t fall apart," he added.
Studying the detailed structure of these asteroids involves more than just
scientific curiosity, Scotti said. There are two practical reasons for
learning more about them: Asteroid minerals can provide raw materials for
future space construction, and knowing how asteroids are put together
provides critical knowledge for deflecting large ones headed for Earth.
Each month, Spacewatch _ the world_s first telescope dedicated to searching
for near-Earth asteroids _ finds an average of two-to-three asteroids in
our vicinity, and another 2,000 new ones in the asteroid belt. Spacewatch
is funded by NASA, the University of Arizona and private donors.