[meteorite-list] Name 'em Mark and Anthony

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Fri, 03 Oct 2008 20:14:26 -0400
Message-ID: <d9dde4he1n749ppvasgv7jtbui8dfnp2of_at_4ax.com>

http://www.space.com/searchforlife/081002-seti-dogbone-asteroid.html

Two Companions Found Near Dog-bone Asteroid

By Franck Marchis
Principal Investigator, SETI Institute, UC Berkeley
posted: 02 October 2008
06:57 am ET

A team of astronomers led by F. Marchis, PI, at the SETI Institute and at
UC-Berkeley, and P. Descamps from Paris Observatory announced recently the
discovery of two moons around an intriguing asteroid. The main-belt asteroid 216
Kleopatra has two companions.

When Marchis observed this asteroid for the first time in October 1999 with the
3.6m telescope at ESO-La Silla in Chile, he did not know that he was starting a
lengthy quest. The first data recorded with an adaptive optics system, which
improves the angular resolution of the image on ground-based telescopes, reveal
that the asteroid was made of two components. One year later, Steve Ostro,
astronomer at the Jet Propulsion Laboratory, published an article in Science
that summarized the analysis of radar observations that revealed that the
mysterious shape of this M-type, main-belt asteroid. Since then, Kleopatra has
been called the "dog-bone" asteroid. Its weird shape is probably the outcome of
an impact event. The two lobes could be fragments resulting from the disruption
of a parent asteroid that later gently collided to form a dumbbell-shaped body
with overall dimension of 135 miles by 58 miles by 43 miles (217 km by 94 km by
81 km).

To reexamine this interesting scenario and better determine the size and shape
of this fascinating asteroid, Marchis led a team that obtained telescope time to
observe the asteroid in September 2008. The observing schedule allowed the team
to take advantage of the asteroid's position when it was close to Earth at 1.2
AU. They used the Keck-II telescope, the largest optical telescope in the world
located on the top of Mauna Kea, in Hawaii. The Keck Adaptive Optics system was
recently improved and its large 10-m aperture produces images with an
incomparable quality in sharpness (resolution up to 0.035"). Using the time-zone
difference, Marchis' collaborator, Pascal Descamps, located in Paris, France,
participated remotely in the observations. Shortly after the first images were
recorded and processed, they realized that the dog-bone shape model obtained by
radar inversion agreed with the direct images recorded at the telescope.
Descamps also pointed out that a tiny 3.1 mile- (5 km-) sized moon was seen on
the first images of Kleopatra. Additional data taken during this eventful night
revealed a second fainter satellite (2.9 mile- or 3 km-sized) that was closer to
the primary.

Because of its elongated and bilobated shape, the team expected to detect
companions around 216 Kleopatra. They predicted that the rubble-pile structure
of the primary, linked with its fast rotation (~5 h), could result in ejection
of fragments from the primary after an oblique impact that formed satellites. It
is also possible that these moons are remnant of the catastrophic disruption of
the parent asteroid, which were subsequently captured.

In 2005 the same team discovered in the asteroid belt the first triple system
composed of two moons around 87 Sylvia. Two years later, a second triple system
(45 Eugenia) was discovered in the main-belt also using an adaptive optics
system. These three systems are strikingly similar since all of them are
composed of a large primary (diameter larger than 54 miles or 100 km) and their
km-sized moons orbit very close to the primary. Without the improvement in image
quality provided by the adaptive optics systems installed on Keck's telescopes,
these multiple asteroid systems would have remained unnoticed.

The team announced its discovery in an IAU circular 8980 on September 24. If
more data are collected over the next few weeks, it will be possible to estimate
the mutual orbits of the satellites and then infer the bulk density of this
interesting M-type asteroid.
Received on Fri 03 Oct 2008 08:14:26 PM PDT