762 Pulcova
Discoverer |
G. N. Neujmin - 1913 |
Diameter (km) |
137.1 |
Mass (kg) |
? |
Rotation period (hrs) |
? |
Orbital period (yrs) |
?
|
Semimajor axis (AU) |
3.16028 |
Orbital eccentricity |
0.09606 |
Orbital Inclination (deg) |
13.04705 |
Albedo |
0.05 |
Type |
C |
Named for Pulkovo, the locality near St. Petersburg (the former Leningrad), where the famous observatory was erected in 1839. Large telescopes with deformable optics are allowing astronomers to study
distant asteroids
with unprecedented clarity -- leading to the discovery of new shapes and
configurations and presenting scientists with new puzzles to solve. An
international team of astronomers led by Dr. William Merline of the Boulder
office of Southwest Research Institute (SwRI) released the first-ever
images of a large, double asteroid.
Each asteroid
in the pair is the size of a large city (about 85 kilometers across),
separated by about 160 kilometers, mutually orbiting the vacant point
of interplanetary space that lies midway between them. The discovery was
made using the W.M. Keck Observatory atop Mauna Kea, the tallest mountain
in Hawaii. The asteroid
pair was once assumed to be a single body, called Antiope,
orbiting the sun in the outer parts of the asteroid
belt between the orbits of Mars and Jupiter. The team also released a
picture of a small moon orbiting the large asteroid
Pulcova. This moon was discovered in February 2000 using the Canada-France-Hawaii
Telescope (CFHT), also on Mauna Kea. It is only the third asteroid
discovered to have a small moon. Asteroid-moon pairs had not been seen
until 1993, when the Galileo
spacecraft imaged the one-mile-wide moonlet Dactyl,
as it rushed past the 58 kilometers diameter asteroid Ida.
The Merline team reported the second asteroidal moonlet a year ago, circling
the 213 kilometers sized asteroid Eugenia.
The team named the companion Petit-Prince,
officially accepted by the International Astronomical Union in August.
"It's getting to be kind of bewildering," says Dr. Christophe Dumas of
the Jet Propulsion Laboratory (JPL), a team astronomer. "Asteroids
were once thought to be single, mountain-like chunks of material, perhaps
smashed into 'flying rubble piles' by occasional collisions among themselves."
Astronomers expect strange new configurations to provide still more surprises
as the survey continues. "Every new asteroidal companion we discover seems
to bring new configurations and new mysteries," says team member Dr. Clark
R. Chapman, also of the SwRI Boulder office. The team's approach uses
a new technology, called adaptive optics, which enables telescopes to
see asteroids
and other small points of light in the heavens with the same clarity as
the Hubble Space Telescope. Until recently, ground-based telescopes were
hindered by distortions caused by Earth's atmosphere, in much the same
way water distorts the view of an underwater object. The new technique
passes light from the telescope through a specialized "correction box"
to instantaneously analyze the distorted light and compute the amount
of correction necessary to remove the blurring of the atmosphere. The
correction information is then fed to deformable mirrors in the box that
remove the distortion, providing a sharper image. A fascinating demonstration
of the new telescope technology is in a movie of the asteroid
Kleopatra, also
released today, observed during a seven-hour period. Earlier this year,
Steve Ostro of JPL published reconstructions of Kleopatra's
shape based on radar reflections obtained when that asteroid was fairly
close to the Earth in November 1999. During the same month, team member
Dr. Francois Menard, currently a visiting scientist at CFHT, obtained
adaptive optics images. "Excellent agreement of both optical and radar
pictures of Kleopatra's
'dog-bone' shape provides added confidence in the reliability of adaptive
optics images," says Menard. "Radar works well for asteroids
near the Earth, but adaptive optics is much more powerful for studying
asteroids
in the middle of the asteroid
belt and beyond," says Dr. Laird Close of the European Southern Observatory
and the University of Arizona. This week, Merline and his colleagues reported
to an annual meeting of international scientists specializing in solar
system studies on two years of asteroid
surveys conducted at three observatories equipped with the new adaptive
optics systems. "In fact, large asteroidal satellites and twin companions
are rather rare," Merline told attendees of the 32nd annual meeting of
the American Astronomical Society's Division for Planetary Sciences, convened
this week in Pasadena, California. "Preliminary study of about 200 asteroids
has turned up only two asteroids with moons (Eugenia
and Pulcova) and just one double (Antiope),"
he explains. "It is possible that a few more moonlets might emerge from
more sophisticated analysis of the data we have collected." Pulcova is
an asteroid
about 90 miles in diameter. Its small satellite, roughly a 10th its size,
orbits Pulcova every four days at a distance of about 500 miles. Asteroidal
companions provide vital information about asteroids
that has been difficult to obtain. Until now, the best measurements of
asteroid
masses -- their bulk densities, such as whether they are "light" like
ice, "dense" like metal, or in between like rocks -- came from deflections
of spacecraft flying past an asteroid.
Such spacecraft encounters are rare, and deflections of more distant objects
(other asteroids or planets) by an asteroid's gravity are weak and difficult
to measure. But an asteroidal satellite, or twin, is a body whose trajectory
is so mightily deflected by the asteroid's gravity that it is actually
forced to orbit around it. The revolution time provides a measure of the
body's mass, hence density. Using such techniques, Merline's team find
that Eugenia, Pulcova,
and Antiope are all
rather light bodies. They are much less dense than familiar rocks, more
like ice, but their surfaces appear very dark, like rock. Interesting
differences in the densities motivate further research on asteroids with
satellites. |
Images of Pulcova |
Image of asteroid
762 Pulcova and its small moon, obtained on 22 February 2000 with the
Canada-France-Hawaii Telescope.
|
Last updated: March 15, 2002.