[meteorite-list] RE: First Triple Asteroid System Found

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Aug 11 01:57:36 2005
Message-ID: <42FAE8A7.769FC926_at_bhil.com>

Hi,

    Besides being delightful in itself, the first thing I
thought of was that low-eccentricity, co-planar satellite
orbits have long been regarded as a "proof" of "formation
in place," as in the Gallilean satellites of Jupiter, which I,
in contrast, believe are captured Plutonian planets,
just to keep riding my newest hobby-horse.

    Well, it's hardly likely that Old Sylvie is the center
of her own little "solar system"! So, such orbits don't
"prove" very much as to how they were formed, it seems.

    The second thought was: do you suppose that, in
addition to a satellite system, Sylvie the Asteroid has
an Asteroid Zone of her own? This falls into the "really
confusing" category right next to "Why does Pluto, an
anthropormorphized cartoon dog, have another, less-
human cartoon dog as a pet?"

    Only partly in humor, but semi-seriously, too,
I suggest a sensitive infra-red image search could
reveal a ring of smaller bodies or particles around
87 Sylvia, orbiting in that same plane...

    Seriously, the low-eccentricity, co-planar satellite
orbits argue a lack of perturbations and a long residence
for these satellites.

Sterling
-----------------------------------------------



> >
> > Rubble-Pile Minor Planet Sylvia and Her Twins
> > VLT NACO Instrument Helps Discover First Triple Asteroid
> >
> > One of the thousands of minor planets orbiting the Sun has been found
> > to have its own mini planetary system. Astronomer Franck Marchis
> > (University of California, Berkeley, USA) and his colleagues at the
> > Observatoire de Paris (France) [1] have discovered the first triple
> > asteroid system - two small asteroids orbiting a larger one known since
> > 1866 as 87 Sylvia [2].
> >
> > "Since double asteroids seem to be common, people have been looking for
> > multiple asteroid systems for a long time," said Marchis. "I couldn't
> > believe we found one."
> >
> > The discovery was made with Yepun, one of ESO's 8.2-m telescopes of the
> > Very Large Telescope Array at Cerro Paranal (Chile), using the
> > outstanding image' sharpness provided by the adaptive optics NACO
> > instrument. Via the observatory's proven "Service Observing Mode",
> > Marchis and his colleagues were able to obtain sky images of many
> > asteroids over a six-month period without actually having to travel to
> > Chile.
> >
> > One of these asteroids was 87 Sylvia, which was known to be double
> > since 2001, from observations made by Mike Brown and Jean-Luc Margot
> > with the Keck telescope. The astronomers used NACO to observe Sylvia on
> > 27 occasions, over a two-month period. On each of the images, the known
> > small companion was seen, allowing Marchis and his French colleagues to
> > precisely compute its orbit. But on 12 of the images, the astronomers
> > also found a closer and smaller companion. 87 Sylvia is thus not double
> > but triple!
> >
> > Because 87 Sylvia was named after Rhea Sylvia, the mythical mother of
> > the founders of Rome, Marchis proposed naming the twin moons after
> > those founders: Romulus and Remus. The International Astronomical Union
> > approved the names.
> >
> > Sylvia's moons are considerably smaller, orbiting in nearly circular
> > orbits and in the same plane and direction. The closest and newly
> > discovered moonlet, orbiting about 710 km from Sylvia, is Remus, a body
> > only 7 km across and circling Sylvia every 33 hours. The second,
> > Romulus, orbits at about 1360 km in 87.6 hours and measures about 18 km
> > across.
> >
> > The asteroid 87 Sylvia is one of the largest known from the asteroid
> > main belt, and is located about 3.5 times further away from the Sun
> > than the Earth, between the orbits of Mars and Jupiter. The wealth of
> > details provided by the NACO images show that 87 Sylvia is shaped like
> > a lumpy potato, measuring 380 x 260 x 230 km and spinning at a rapid
> > rate, once every 5 hours and 11 minutes.
> >
> > The observations of the moonlets' orbits allow the astronomers to
> > precisely calculate the mass and density of Sylvia. With a density only
> > 20% higher than the density of water, it is likely composed of water
> > ice and rubble from a primordial asteroid. "It could be up to 60
> > percent empty space," said co-discoverer Daniel Hestroffer
> > (Observatoire de Paris, France).
> >
> > "It is most probably a "rubble-pile" asteroid", Marchis added. These
> > asteroids are loose aggregations of rock, presumably the result of a
> > collision. Two asteroids smacked into each other and got disrupted.
> > "The new rubble-pile asteroid formed later by accumulation of large
> > fragments while the moonlets are probably debris left over from the
> > collision that were captured by the newly formed asteroid and
> > eventually settled into orbits around it. Because of the way they form,
> > we expect to see more multiple asteroid systems like this."
> >
> > Marchis and his colleagues will report their discovery in the August 11
> > issue of the journal Nature, simultaneously with an announcement that
> > day at the Asteroid Comet Meteor conference in Arma??o dos B?zios, Rio
> > de Janeiro state, Brazil.
> >
> > More information
> > Two images are available with this press release. They are available
> > from the ESO Press Office during the embargo period. When the embargo
> > is lifted they will be available, together with the full text of this
> > press release at
> > http://www.eso.org/outreach/press-rel/pr-2005/pr-21-05.html
> >
> > A computer animation in broadcast quality is also available at
> > ftp://ftp.eso.org/pub/general/hboffin/Asteroid.mov (739 MB).
> > A preview is available at
> > ftp://ftp.eso.org/pub/general/hboffin/Asteroid-low.mov (13 MB).
> >
> > Notes
> > [1] The team is composed of Franck Marchis (University of California,
> > Berkeley, USA) and Pascal Descamps, Daniel Hestroffer, and Jerome
> > Berthier (Observatoire de Paris, France).
> > [2] 87 Sylvia is the 87th minor planet discovered. It was first
> > detected from the Observatory of Madras (India) on May 16, 1866, by the
> > Government Astronomer Norman R. Pogson. It was common in the early days
> > to assign a name - mostly feminine - from the mythology to newly found
> > asteroids. Pogson selected a name from the list furnished to him by Sir
> > John Herschel.
> >
> > Contacts
> > Franck Marchis
> > University of California, Berkeley, USA
> > Phone: +1 (510) 642 3958 or +1 (510) 599 0604
> > Email: fmarchis_at_berkeley.edu
> >
> > Pascal Descamps, Daniel Hestroffer, Jerome Berthier
> > IMCCE, Observatoire de Paris, France
> > Phone: +33 1 4051 2268 or +33 1 4051 2260
> > Email: descamps_at_imcce.fr, hestroffer@imcce.fr, berthier@imcce.fr
> >
> > Henri Boffin
> > ESO Press Office
> > Public Affairs Dept.
> > Phone: +49 89 3200 6222
> > Email: hboffin_at_eso.org
Received on Thu 11 Aug 2005 01:56:55 AM PDT