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Topic: Protoplanetary disc

	Protoplanetary disc - Biocrawler (Site not responding. Last check: 2007-10-16)
		A protoplanetary disc (also protoplanetary disk, proplyd) is an accretion disc surrounding a T Tauri star.
		Disc accretion continues for another 10 million years, before the disc disappears, which means that it is either really gone or just does not emit radiation any more because accretion has ceased.
		Protoplanetary discs are thought to be the progenitors of planetary systems.
	www.biocrawler.com /encyclopedia/Proplyd (257 words)

	CONK! Encyclopedia: Protoplanetary_disc (Site not responding. Last check: 2007-10-16)
		A protoplanetary disc (also protoplanetary disk, proplyd) is an accretion disc surrounding a T Tauri star.
		Disc accretion continues for another 10 million years, before the disc disappears, which means that it is either really gone or just does not emit radiation any more because accretion has ceased.
		Protoplanetary discs are thought to be the progenitors of planetary systems.
	www.conk.com /search/encyclopedia.cgi?q=Protoplanetary_disc (251 words)

	Disk - Wikipedia, the free encyclopedia
		In biology, an intervertebral disc is a cartilaginous joint between vertebrae in the spine of vertebrate animals.
		In astrophysics, an accretion disc or disk is a structure formed by material falling into a gravitational source.
		Disc came into the English language in the mid-17th century, from the Latin discus, and like already-existing words like whisc or risc, it was spelled with c; disk arose some time later, and was based on the original Greek root diskus.
	en.wikipedia.org /wiki/Disk_or_disc (517 words)

	Dynamos in the protoplanetary accretion disc (Site not responding. Last check: 2007-10-16)
		Furthermore, the low temperature in the extensive parts of a protoplanetary disc translates into the low ionisation regime, which is maintained by nonthermal ionisation processes (Umebayashi and Nakano 1988 [24], Stepinski 1992 [22]).
		The opacity law, needed to determine the structure of the steady-state disc, is taken from Ruden and Pollack (1991) [18].
		On the smaller scale, the structure of the poloidal field in protoplanetary and standard discs differs because of the existence of the magnetic gap region in the former.
	www.lpi.usra.edu /science/tom/mn/node5.html (1355 words)

	ESO - 2004
		Accordingly, the dust in the disc regions that are closest to the star is soon transformed from "pristine" (small and amorphous) to "processed" (larger and crystalline) grains.
		The general broadening of the spectral "mountain" in the inner discs is a sign of larger grains and the spectral peak at wavelength 11.3 µm indicates the presence of crystalline silicates, cf.
		Earlier observations of discs around young stars have shown a mixture of pristine and processed material to be present, but it was so far impossible to tell where the different grains resided in the disc.
	www.eso.org /outreach/press-rel/pr-2004/pr-27-04.html (1645 words)

	CEA - English portal - News list - Anatomy of a protoplanetary disc
		Astrophysicists from CEA/Dapnia and the University of Paris 7, in collaboration with the Grenoble Astrophysics Laboratory, the Orsay Space Astrophysics Institute and the University of Groeningen in the Netherlands, have succeeded in mapping the disc surrounding the star HD 97048.
		The geometry of this disc is unusual in that it is not flat, but widens out as the distance from the star increases, reaching an eventual thickness of 360 astronomical units.
		In the coming months, this disc will be the target of a number of observation programmes, with the particular aim of zooming in on internal denser regions of the disc where embryonic planets may already have formed.
	www.cea.fr /english_portal/news_list/anatomy_of_a_protoplanetary_disc (705 words)

	Protoplanetary disc (Site not responding. Last check: 2007-10-16)
		A protoplanetary disc (also protoplanetary disk, proplyd) is a disc of dust and gas which orbit s a protostar, within a solar nebula.
		Disc Jam London, England event comprised of competitions in disc golf, ultimate frisbee, goaltimate, double disc court and freestyle.
		Disc Golf at ISU Information about the ISU (Idaho State University) Disc Golf Course and disc golf club.
	www.serebella.com /encyclopedia/article-Protoplanetary_disc.html (470 words)

	Accretion Disc (Site not responding. Last check: 2007-10-16)
		This is the first solid observational evidence for star formation in an accretion disc around a fl hole, and it implies that the inner parsecs of galaxies...
		An accretion disk (or accretion disc) is a structure formed by material falling into a gravitational source.
		Protoplanetary discs are referred to as accretion disks when viewed as material falling into the central protostar.
	www.wikiverse.org /accretion-disc (358 words)

	Protoplanetary disc -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-10-16)
		A protoplanetary disc (also protoplanetary disk, proplyd) is an (Click link for more info and facts about accretion disc) accretion disc surrounding a (Click link for more info and facts about T Tauri star) T Tauri star.
		Protoplantary discs have radii up to 1000 (A unit of length used for distances within the solar system; equal to the mean distance between the Earth and the Sun (approximately 93 million miles or 150 million kilometers)) astronomical units and are rather cool.
		Gravitational interactions may cause the dust and gas in the disk to condense into (One of many small solid celestial bodies thought to have existed at an early stage in the development of the solar system) planetesimals.
	www.absoluteastronomy.com /encyclopedia/p/pr/protoplanetary_disc.htm (473 words)

	[No title] (Site not responding. Last check: 2007-10-16)
		Protoplanetary cores, the building blocks of planet formation, condense from the interstellar dust grains that are initially suspended in the gaseous envelope of the disc.
		The body (a protoplanetary core or later stage planet) is embedded in the circumstellar gas disc, and is coupled to it via gravitational interactions.
		The tidal torques exerted by the planet on the disc are known to be localised at a distance comparable to the disc thickness away from the near circular planetary orbit.
	www.maths.qmw.ac.uk /~jdl/ORIGINS/intro.html (939 words)

	Large scale numerical modeling project
		In \cite{Gleaves} the protoplanetary disc is considered as a catalytic chemical reactor for synthesis of primary organic compounds.
		The dynamics of the dust component of protoplanetary disc is described by the Vlasov-Liouville kinetic equation.
		In the full description of the protoplanetary disc these equations are complemented with the equations for chemical reactions in gas phase and the equations for simulation of coagulation processes in the dust component.
	www.invest.sscc.ru /projectsinfo/large_scale.htm (2059 words)

	Encyclopedia: Disc (Site not responding. Last check: 2007-10-16)
		A disk or disc is anything that resembles a flattened cylinder in shape.
		In the 19th century, disc became the conventional spelling for audio recordings made on a flat plate, such as the gramophone record; this usage gave rise to the modern term disc jockey.
		In 1979 the European company Philips, along with Sony, developed the compact disc medium; here, the c-spelling was chosen, possibly because of the predominating British spelling, or because the compact disc was seen as a successor to the analogue disc record.
	www.nationmaster.com /encyclopedia/Disc (438 words)

	Global $\vec{m} = \mathsf{1}$ modes and migration of protoplanetary cores in eccentric protoplanetary discs
		We consider the motion of a protoplanet in the earth mass range embedded in an eccentric disc and determine the equilibrium orbits which maintain fixed apsidal alignment with respect to the disc gas orbits.
		Results are found to deviate from the case of axisymmetric disc with near circular protoplanet orbit once eccentricities of protoplanet and disc orbits become comparable to the disc aspect ratio in magnitude.
		Thus the existence of global non circular motions in discs with radial excursions comparable to the semi-thickness may have important consequences for the migration and survival of protoplanetary cores in the earth mass range.
	www.edpsciences.org /articles/aa/abs/2002/23/aa2149/aa2149.html (332 words)

	Asteroids, Asteroid, Asteroid Belt at SPACE.com
		During the formation of our solar system, hundreds of thousands of particles were pulled by Jupiter’s gravity rather than being spread out through space.
		These minor planets, or asteroids, are the products of the protoplanetary disc — dense rings of gas surrounding a newly formed star.
		Most asteroids orbit within an area between Jupiter and Mars known as the asteroid belt.
	www.space.com /asteroids (423 words)

	Triggered planet formation in massive protoplanetary discs
		The fact that extrasolar planets are common came as no surprise, since the protoplanetary discs of gas and dust that form planets are observed around most young stars.
		These surprising properties have led theorists to believe that interactions between giant planets, and between planets and the protoplanetary disc, are of crucial importance in determining the final structure of planetary systems.
		Discs and planetary formation, a technical review article by John Papaloizou and collaborators for the EU Summer School on 'Astrophysical Discs'.
	www.mpa-garching.mpg.de /HIGHLIGHT/2000/highlight0002_e.html (379 words)

	Radial mixing in protoplanetary accretion disks
		The interplay between radial mixing process in protoplanetary accretion discs with processes leading to destruction or modification of the extinction properties of abundant dust species has significant consequences for the properties of the disk.
		Radial mixing of the freshly produced crystalline silicate dust into outer disc regions reduces the opacity of the disc material also in cold disc regions where annealing is not possible.
		It is shown that turbulent mixing processes in the protoplanetary accretion disc of a Solar System like system during its evolution prior to the onset of the formation of planetary bodies carry material from inner disc regions r< 1 AU outwards to at least 10...20 AU.
	www.edpsciences.org /articles/aa/abs/2001/40/aah2627/aah2627.html (381 words)

	Animations (Site not responding. Last check: 2007-10-16)
		Evolution of a protoplanetary accretion disc in which the cooling time is sufficiently small for fragmentation to occur.
		The evolution of a protoplanetary disc with a mass equal to that of the central star.
		The evolution of a self-gravitating disc undergoing a co-planar encounter with an object with a mass equal to that of the disc and that is in a parabolic orbit.
	faculty.ucr.edu /~krice/animations.html (176 words)

	Sports Fresh : Article 'Protoplanetary disc' (Site not responding. Last check: 2007-10-16)
		It shows an excess of infrared emission compared to normal stars of its class, and detailed observations reveal a large circumstellar disc, often considered to be a protoplanetary disc.
		In the modified version, the mass of the original protoplanet was assumed to be larger, and the angular momentum discrepancy was attributed to magnetic forces.
		In cosmogony, a protoplanet is a quasi-planetoid which is slightly larger than a planetesimal and orbits within a solar nebula's protoplanetary discs.
	www.sports-fresh.net /DisplayArticle214741.html (899 words)

	Accretion disc -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-10-16)
		An accretion disc (or accretion disk) is a structure formed by material falling into a (Movement downward resulting from gravitational attraction) gravitational source.
		Conservation of (The product of the momentum of a rotating body and its distance from the axis of rotation) angular momentum requires that, as a large cloud of material collapses inward, any small rotation it may have will increase.
		(Click link for more info and facts about Protoplanetary disc) Protoplanetary discs are referred to as accretion disks when viewed as material falling into the central (Click link for more info and facts about protostar) protostar.
	www.absoluteastronomy.com /encyclopedia/a/ac/accretion_disc.htm (244 words)

	Bild des Monats (Site not responding. Last check: 2007-10-16)
		Planets are believed to form in protoplanetary discs through the sticking of microscopic dust grains to larger and larger bodies.
		The lengths are given in units of H, is the scale height of the disc, which in a disc with H/r = 0.02 is around 0.1 AU at the location of Jupiter.
		The times are given in units of 1/Omega, which is one rotation period of the disc.
	mpia-hd.mpg.de /Public/Aktuelles/Bild_des_Monats/index_en.html (269 words)

	News in Science - Planet formation may be more commonplace - 13/12/2002
		Young stars with no visible disc of dust and gas, long dismissed as ever likely to develop planets, may still be breeding them - it's just that their planet-forming dust is hard to see, according to two American astronomers.
		Normally, T Tauri stars less than 3 million years old are surrounded by a thick disc of dust and gas, known as a protoplanetary disc because it is a breeding ground for planet formation.
		But most older T Tauri stars show no sign of a disc and, because they are not old enough for planets to form, astronomers have long assumed that these stars had lost their discs before planets could form.
	www.abc.net.au /science/news/stories/s746352.htm (493 words)

	JPL.NASA.GOV: News Releases
		NASA's Spitzer Space Telescope spotted such a disc around a surprisingly low-mass brown dwarf, or "failed star." The brown dwarf is only 15 times the size of Jupiter, making it the smallest brown dwarf known to host a planet-forming, or protoplanetary disc.
		NASA's Spitzer Space Telescope has spotted a dusty disc of planet-building material around an extraordinarily low-mass brown dwarf, or "failed star." The brown dwarf, called OTS 44, is only 15 times the mass of Jupiter.
		The infrared array camera, which spotted the protoplanetary disc around OTS 44, was built by NASA Goddard Space Flight Center, Greenbelt, Md.; its development was led by Fazio.
	www.jpl.nasa.gov /news/news.cfm?release=2005-022 (746 words)

	New Scientist Breaking News - Carbon-rich planets may boast diamond interiors
		The diamond-rich planets could form from the dusty protoplanetary discs found around many stars, if they are rich in carbon and poor in oxygen, says Marc Kuchner at Princeton University, New Jersey, US.
		However, the element is 1000 times more common in chondrite meteorites, which originated in the solar system, though probably in a different region of the protoplanetary disc.
		The key factor behind the difference between carbon and silicate-based planets is the chemistry of the protoplanetary disc.
	www.newscientist.com /article.ns?id=dn6988 (529 words)

	Harvard Archives Show "Winking Star" Started Winking Only Recently (Forwarded)
		That disk, known as a protoplanetary disk, is a possible source of the = eclipses.
		That disk, known as a protoplanetary disk, is a possible source of the eclipses.
		One possibility is that this swath is actually a "ripple" in the protoplanetary disk, recently stirred up by the gravitational influence of an embedded protoplanet.
	www.science-one.com /new-3498541-4253.html (2582 words)

	IGPP-UCR people Ken Rice (Site not responding. Last check: 2007-10-16)
		I use numerical simulations to model gaseous protoplanetary discs around young solar-like stars, in particular discs that may be sufficiently massive for self-gravity to be important.
		Constraints on a planetary origin for the gap in the protoplanetary disc of GM Aurigae, W. Rice, K. Wood, P. Armitage, B. Whitney and J. Bjorkman, Mon.
		The effect of cooling on the global stability of self-gravitating protoplanetary discs, W. Rice, P. Armitage, M. Bate and I. Bonnell, Mon.
	www.igpp.ucr.edu /People_Rice.htm (522 words)

	Image ssc2004-08c
		Spectroscopy involves spreading the light from a star into a spectrum (in visible light, we are familiar with white light being spread out into a rainbow when it passes through a prism), and then measuring exactly how much light is present in each wavelength.
		Going a step further, in the third diagram we see the spectrum of a star with a circumstellar disc around it, but in this case, the inner part of the disc has been swept away, perhaps by the formation of a planet.
		This low temperature "bump" on the spectrum indicates a disc with a missing center, and may be the first clue that planets have formed inside the disc.
	www.spitzer.caltech.edu /Media/releases/ssc2004-08/ssc2004-08c.shtml (461 words)

	IAU Symposium 202 - Poster paper (Site not responding. Last check: 2007-10-16)
		Self gravity, and turbulence driven by magnetic instabilities, are the only known sources of angular momentum transport in protoplanetary discs.
		This has important implications for protoplanetary disc structure at radii of the order of 1 AU, where the disc is typically too weakly ionized to support magnetohydrodynamic turbulence, and not massive enough to be self-gravitating.
		We present time dependent models for the evolution of discs that incorporate these effects, and discuss how they differ from standard protoplanetary disc models.
	astro1.bnsc.rl.ac.uk /symp202/posters/armitage.html (88 words)

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