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Posted by K. M. Kirby, esq. on October 7, 2007, 7:46 pm
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This group seems to be of the opinion that planetary formation only
takes place after solar ignition. Another faction believes that fully
formed planets become illuminated by a new sun, after which point most
of the protoplanetary dust disc is removed in the solar wind.
baa...@earthlink.net wrote:
> http://www.rochester.edu/news/show.php?id=2993
>
> University of Rochester
>
> MEDIA CONTACT: Jonathan Sherwood (585) 273-4726,
> jonathan.sherwood@rochester.edu
>
> October 1, 2007
>
> Sign of 'Embryonic Planets' Forming in Nearby Stellar Systems
>
> Astronomers at the University of Rochester are pointing to three
> nearby
> stars they say may hold "embryonic planets" - a missing link in
> planet-formation theories.
>
> As scientists try to piece together how our own planet came to be,
> they
> look to the forming planets of other star systems for clues. But
> astronomers have been unable to find evidence for one of the key
> stages
> of planet development, a period early in the planet's formation when
> it
> is only as large as tiny Pluto.
>
> In an attempt to reveal this hidden phase of a planet's life, Alice
> Quillen, associate professor of astronomy at the University of
> Rochester, employed new Hubble Space Telescope imagery to measure the
> thickness of the dust disks that surround forming stars, and to
> calculate the size of the planets growing within.
>
> The results help paint a picture of a planet's earliest years, and
> tell
> us how our own small planet probably began its life, says Quillen.
>
> Scientists have inferred the presence of nearly 250 planets in the
> last
> decade, but Quillen's method focuses on a unique aspect: the
> proto-planetary disk's thickness.
>
> Quillen explains that a disk of gritty dust usually surrounds forming
> stars, and provides the raw material for planet building. The cloud of
> dust thins as the system ages, but if enough dust has clumped
> together,
> the "embryonic planet," as Quillen calls it, will knock the dust and
> grit into ever-more eccentric orbits. Over time, this will cause an
> otherwise razor-thin disk to appear puffed up.
>
> "We're able to determine for the first time how large the bodies must
> be
> in a disk to scatter the dust the way we've observed," says Quillen,
> one
> of the world's leading experts on the interaction between planets and
> stellar dust disks.
>
> Using new Hubble images, Quillen measured the "puffiness" of AU
> Microscopii, Beta Pictoris, and Fomalhaut - three nearby stars with
> young
> disks positioned edge-on toward Earth. All three stars displayed a
> thicker disk than conventional models anticipated, so Quillen stepped
> beyond those models.
>
> Dust disks have a lifespan determined by a balance of how quickly the
> solar wind blows the dust away, and how quickly the largest "grit
> clumps" replenish the dust through their collisions, says Quillen.
> Based
> on this balance, the size and age of a disk reveal how large the
> clumps
> inside must be.
>
> But the conventional theory doesn't take a disk's thickness into
> account
> because until the Hubble images, astronomers had no way to measure it.
> Thus, the largest "clump" the model could predict was about a
> kilometer
> wide - a far cry from the fully grown planets that emerge from such
> disks.
>
> Armed with the new images and her own models of dust dynamics, Quillen
> estimated how much mass was required to gravitationally scatter the
> dust
> to the thicknesses she observed.
>
> "Those calculations pushed us into Pluto-sized bodies," says Quillen.
> At
> roughly 1,000 kilometers in size - and owing to Pluto's recent
> demotion
> from planethood - Quillen dubbed these new bodies, embryonic planets.
>
> Quillen is now looking for more young star systems to investigate with
> her model, but the criteria for candidates is quite strict. The
> systems
> have to be young enough to still have their protostellar disks, but
> old
> enough to be forming the embryonic planets. The systems must also
> appear
> edge-on from Earth and be near enough that Hubble can accurately
> discern
> the thickness of their disks. At the moment, the three stars Quillen
> has
> already observed appear to be the only candidates that meet all the
> standards.
>
> This research was funded in part by the National Science Foundation.
>
> About the University of Rochester
>
> The University of Rochester (www.rochester.edu) is one of the nation's
> leading private universities. Located in Rochester, N.Y., the
> University
> gives students exceptional opportunities for interdisciplinary study
> and
> close collaboration with faculty through its unique cluster-based
> curriculum. Its College of Arts, Sciences, and Engineering is
> complemented by the Eastman School of Music, Simon School of Business,
> Warner School of Education, Laboratory for Laser Energetics, Schools
> of
> Medicine and Nursing, and the Memorial Art Gallery.
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