[meteorite-list] Comet Crystals Found in a Nearby Planetary System

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 3 Oct 2012 11:55:09 -0700 (PDT)
Message-ID: <201210031855.q93It95p009905_at_zagami.jpl.nasa.gov>

http://www.esa.int/esaSC/SEMSLRERI7H_index_0.html

Comet crystals found in a nearby planetary system
European Space Agency
3 October 2012

Pristine material that matches comets in our own Solar System have been
found in a dust belt around the young star Beta Pictoris by ESA's
Herschel space observatory.
 
Twelve-million-year-old Beta Pictoris resides just 63 light-years from
Earth and hosts a gas giant planet along with a dusty debris disc that
could, in time, evolve into a torus of icy bodies much like the Kuiper
Belt found outside the orbit of Neptune in our Solar System.

Thanks to the unique observing capabilities of Herschel, the composition
of the dust in the cold outskirts of the Beta Pictoris system has been
determined for the first time.

Of particular interest was the mineral olivine, which crystallises out
of the protoplanetary disc material close to newborn stars and is
eventually incorporated into asteroids, comets and planets.

"As far as olivine is concerned, it comes in different 'flavours',"
explains Ben de Vries from KU Leuven and lead author of the study
reported in Nature.

"A magnesium-rich variety is found in small and primitive icy bodies
like comets, whereas iron-rich olivine is typically found in large
asteroids that have undergone more heating, or 'processing'."
 
Herschel detected the pristine magnesium-rich variety in the Beta
Pictoris system at 15-45 astronomical units (AUs) from the star, where
temperatures are around -190??C.

For comparison, Earth lies at 1 AU from our Sun and the Solar System's
Kuiper Belt extends from the orbit of Neptune at about 30 AU out to 50
AU from the Sun.

The Herschel observations allowed astronomers to calculate that the
olivine crystals make up around 4% of the total mass of the dust found
in this region.

In turn, this finding led them to conclude that the olivine was
originally bound up inside comets and released into space by collisions
between the icy objects.

"The 4% value is strikingly similar to that of Solar System comets
17P/Holmes and 73P/Schwassmann-Wachmann 3, which contain 2-10%
magnesium-rich olivine," says Dr de Vries.

"Since olivine can only crystallise within about 10 AU of the central
star, finding it in a cold debris disc means that it must have been
transported from the inner region of the system to the outskirts."

The "radial mixing" transport mechanism is known from models of the
evolution of swirling protoplanetary discs as they condense around new
stars.

The mixing is stimulated in varying amounts by winds and heat from the
central star pushing materials away, along with temperature differences
and turbulent motion created in the disc during planet formation.

"Our findings are an indication that the efficiency of these transport
processes must have been similar between the young Solar System and
within the Beta Pictoris system, and that these processes are likely
independent of the detailed properties of the system," says Dr de Vries.

Indeed, Beta Pictoris is over one and a half times the mass of our Sun,
eight times as bright, and its planetary system architecture is
different to our own Solar System today.

"Thanks to Herschel, we were able to measure the properties of pristine
material left over from the initial planet-building process in another
solar system with a precision that is comparable to what we could
achieve in the laboratory if we had the material here on Earth," says
ESA's Herschel project scientist G??ran Pilbratt.
 
 
Notes for Editors <http://www.esa.int/esaSC/SEMKMRERI7H_index_0.html>
 
Received on Wed 03 Oct 2012 02:55:09 PM PDT