PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
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Contact: Jim Doyle

EMBARGOED FOR RELEASE AT 6 P.M. EASTERN TIME, OCTOBER 5, 1995

TOUTATIS ONE OF THE STRANGEST OBJECTS IN THE SOLAR SYSTEM

     Two NASA-sponsored scientists studying the Earth-crossing 
asteroid 4179 Toutatis with radio telescopes have found it to be 
one of the strangest objects in the solar system, with a highly 
irregular shape and an extraordinarily complex "tumbling" 
rotation.

     Both its shape and rotation are thought to be the outcome of 
a history of violent collisions.  A detailed description of the 
asteroid and its observed rotation are reported in this week's 
issue of the journal Science, by Drs. Scott Hudson of Washington 
State University and Steven Ostro of NASA's Jet Propulsion 
Laboratory, Pasadena, CA.

     "The vast majority of asteroids, and all the planets, spin 
about a single axis, like a football thrown in a perfect spiral," 
Hudson said, "but Toutatis tumbles like a flubbed pass."

     One consequence of this strange rotation is that Toutatis 
does not have a fixed north pole like the Earth.  Instead, its 
north pole wanders along a curve on the asteroid about every 5.4 
days. "The stars viewed from Toutatis wouldn't repeatedly follow 
circular paths, but would crisscross the sky, never following the 
same path twice," Hudson said.

     "The motion of the Sun during a Toutatis year, which is 
about four Earth years, would be even more complex," he 
continued. "In fact, Toutatis doesn't have anything you could 
call a 'day.' Its rotation is the result of two different types 
of motion with periods of 5.4 and 7.3 Earth days that combine in 
such a way that Toutatis's orientation with respect to the solar 
system never repeats."

     The rotations of hundreds of asteroids have been studied 
with optical telescopes. The vast majority of them appear to be 
in simple rotation with a fixed pole and periods typically 
between one hour and one day, the scientists said, even though 
the violent collisions these objects are thought to have 
experienced would mean that every one of them, at some time in 
the past, should have been tumbling like Toutatis.

     Internal friction has caused them to change into simple 
rotational patterns in relatively brief amounts of time. However, 
Toutatis rotates so slowly that this "dampening" process would 
take much longer than the age of the solar system. This means 
that the rotation of Toutatis is a remarkable, well-preserved 
relic of the collision-related evolution of an asteroid.

     Hudson and Ostro used radar images obtained with the Deep 
Space Network Goldstone radar antenna in California and the 
Arecibo telescope in Puerto Rico in 1992, when Toutatis passed to 
within a little more than 2 million miles of the Earth.  The 
images are reported in a companion paper, also in this week's 
issue of Science.

     Toutatis was discovered by French astronomers in 1989 and 
was named after a Celtic god that was the protector of the tribe 
in ancient Gaul.  Its eccentric, four-year orbit extends from 
just inside the Earth's orbit to the main asteroid belt between 
Mars and Jupiter. The plane of Toutatis's orbit is closer to the 
plane of the Earth's orbit than any known Earth-orbit-crossing 
asteroid.

     On September 29, 2004, Toutatis will pass four lunar 
distances from Earth, the closest approach of any known asteroid 
or comet between now and 2060. One consequence of the asteroid's 
frequent close approaches to Earth is that its trajectory more 
than several centuries from now cannot be predicted accurately.  
In fact, of all the Earth-crossing asteroids, Toutatis's orbit is 
thought to be one of the most chaotic.

     Earth-crossing asteroids are of great interest to scientists 
for their relationships to meteorites, main-belt asteroids and 
comets; as targets of human or robotic exploration; as sources of 
materials with potential commercial value; and as long-term 
collision hazards.
Nearly 300 Earth-crossing asteroids have been discovered, but the 
entire population is thought to include some 1,500 objects larger 
than one kilometer and some 135,000 objects that are larger than 
100 meters.

     The scientists' work was funded by the Planetary Geology and 
Geophysics Program and the Planetary Astronomy Program of NASA's 
Office of Space Science, Washington, D.C.

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10/5/95 JJD
#9567