Douglas Isbell
Headquarters, Washington, DC          October 5, 1995
(Phone: 202/358/1547)                 EMBARGOED FOR RELEASE AT 6 P.M. EDT

Jim Doyle
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-5011)

RELEASE: 95-171

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 is
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 (JPL), 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 asteroids 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.

        The scientists' computer model reveals Toutatis to have
dimensions of  2.9 miles by 1.5 miles by 1.2 miles.  Numerous
surface features, including a pair of half-mile-wide craters,
side by side, and a series of three prominent ridges -- a type
of asteroid mountain range -- are presumed to result from a
complex history of impacts.

        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 by Earth at a
range of four times the distance between the Earth and the
Moon, 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,  the orbit of
Toutatis 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, DC.