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	General dictionary - Planetesimal (Site not responding. Last check: 2007-10-20)
		Planetesimals are objects of some Km of diameters that are thought to have formed during the solar system's formation.
		These planetseimals have a composition that depends on the region where they have formed (we find rocky planetesimals in the inner parts and ices in the outer parts) and are the "bricks" of the following formation of the planets.
		Asteroids and comets are leftover planetesimals that have not been incorporated into a planet during this period.
	www.ecology.com /archived-links/planetesimals/index.html (110 words)

	Planetesimal
		In cosmogony, planetesimals are objects thought to exist within solar nebulae.
		Planetesimals are thought to form from the coalescing (due to gravity) of particles, orbiting within the accretion disc of the solar nebula; an accumulation of planetesimals leads to the formation of a protoplanetary disc, which in turn coalesce into protoplanets/planets.
		It is generally argued that by about 3.8 billion years ago most of the planetesimals, within Sol's system, had either left orbit or coalesced into larger objects.
	www.ebroadcast.com.au /lookup/encyclopedia/pl/Planetesimal.html (128 words)

	Zoe Malka Leinhardt
		However, planetesimals, which are large enough to decouple from the gaseous nebula, are dominated by self-gravity not material strength.
		The planetesimals are modeled as rubble piles which are gravitational aggregates of indestructible particles bound together purely by gravity.
		I then incorporated the planetesimal collision model into global planet formation simulations with varying initial conditions to determine the range of terrestrial planets that are formed.
	www.people.fas.harvard.edu /~zmleinh/research/planet.html (704 words)

	Planetesimal - Wikipedia, the free encyclopedia
		Planetesimals are solid objects thought to exist in protoplanetary disks and in debris disks.
		A few planetesimals may have been captured as moons, such as Phobos and Deimos (the moons of Mars), and many of the small high-inclination moons of the Jovian planets.
		A planetesimal is a solid object arising during the accumulation of planets whose internal strength is dominated by self-gravity and whose orbital dynamics is not significantly affected by gas drag.
	en.wikipedia.org /wiki/Planetesimal (572 words)

	Stellar Flybys and Icy Formation
		Planetesimals with sizes of 1-10 km probably shatter at velocities of 200 m/sec.
		The planetesimals and most of the dust lie in a thin layer at the midplane of the disk.
		In a planetesimal disk, the grains are so numerous that their reflected light can be observed on Earth, as a disk of dusty debris around a nearby star.
	cfa-www.harvard.edu /~kenyon/pf/dd/flyby.html (1060 words)

	The Evolution of the Stars and the Formation of the Earth - HYPOTHESIS
		The planetesimal hypothesis attributes this equatorial acceleration to the falling back into the Sun of the materials which had been lifted out to a short distance by the disturbing body, and to the forward-rushing tide raised in the equatorial regions by the disturbing body.
		The point is not necessarily in opposition to the planetesimal hypothesis; but whatever the explanation, it ought to apply to the planet as well as to the Sun.
		To this extent the planetesimal hypothesis does not furnish a good explanation of the origin of comets, unless we assume that a small amount of matter was widely scattered in all directions around the parent spiral; and this conception leads to some apparent difficulties.
	www.worldwideschool.org /library/books/sci/astronomy/TheEvolutionOfTheStarsAndTheFormationOfTheEarth/chap2.html (2199 words)

	Dusty Rings and Icy Planet Formation
		In the planetesimal theory, planets grow from collisions and mergers of smaller bodies, planetesimals, embedded in the disk.
		Because a few of the largest planetesimals grow much faster than any of their neighbors, this phase is often called runaway growth.
		Planetesimals begin to grow at the inner edge of the disk; the inner disk becomes fainter at t = 3 Myr.
	cfa-www.harvard.edu /~kenyon/pf/dd (1159 words)

	THE ANIMATE AND THE INANIMATE, Chapter 13
		The Planetesimal Hypothesis thus tends to assume that the universe always was somewhat as it is now, but that stars come and go in generations, as it were.
		In the case of the earth, for instance, it is supposed that the earth was rotating with extreme rapidity, the centrifugal force finally elongating it into a sort of pear-shape, the elongation continuing until the centrifugal force at the end of the earth at the smaller end of the "pear" separated and became the moon.
		This is hardly in accord with either the Nebular or Planetesimal Hypothesis, for, on the first, light would not be a sudden development, and, on the second, both light and nebula originate at the same time, the light reaching outside points long before the nebula.
	www.sidis.net /ANIM13.htm (2628 words)

	chapter 13
		When planetesimals are accreting prior to runaway accretion their size distribution will no doubt be a continuous function, probably of the kind we find among the asteroids.
		Before and during the runaway phase, however, the embryo accretes planetesimals, some of which are of a size comparable to that of the embryo.
		Hence, a random spin vector due to the statistical arrival of large planetesimals is superimposed upon the spin vector which in the Giuli case is perpendicular to the orbital plane.
	history.nasa.gov /SP-345/ch13.htm (3282 words)

	Our Research
		At the same time there is a planetesimal an order of magnitude further away from Jupiter and he is bopping along with no interactions with other planetesimals, taking 5000 steps per orbit.
		It does this by considering "how much" the planetesimal is interacting with its surroundings; the surroundings being Jupiter and the other, sometimes larger, planetesimals and then assigns a certain timestep to each planetesimal based on that interaction.
		As we began to examine other aspects of joviangrav, we confronted two problems, one was a numerical problem that was solved by adjusting the parameter eta, and one was a fundamental problem that comes along with the non-symplectic nature of the multistepping process.
	www-hpcc.astro.washington.edu /faculty/trq/galmoons/research.html (2749 words)

	Accelerated planetesimal growth in self-gravitating protoplanetary discs
		The drag force between the disc gas and the embedded planetesimals generally causes the planetesimals to drift inwards through the disc at a rate that depends on the particle size.
		In a marginally stable, self-gravitating disc, however, the planetesimals are significantly influenced by the non-axisymmetric spiral structures resulting from the growth of the gravitational instability.
		Although at the end of the simulation only 25 per cent of the planetesimal particles lie in regions of enhanced density, during the course of the simulation at least 75 per cent of the planetesimal particles have at some stage been in a such a region.
	repositories.cdlib.org /postprints/55 (412 words)

	[23.02] Planetesimal clustering in protoplanetary disks (Site not responding. Last check: 2007-10-20)
		The usual approach to the study of planetary accretion always considers homogeneous distributions of planetesimals and isotropic velocity dispersions.
		Nevertheless, if small planetesimals (in the 1 cm - 1 m range) were affected by the turbulent gas disk motion, several studies have suggested that the properties of homogeneity could be easily lost (see e.g.
		An appropriate rescaling of these results toward planetesimals of smaller sizes shows that cluster survival is relevant in affecting their dynamics, collisional properties and growth rate.
	www.aas.org /publications/baas/v33n3/dps2001/439.htm (272 words)

	The Barrel of Fire
		A planetesimal falling almost vertically to the surface at 20 kilometres a second would take less than 2 seconds to pass through the denser region of the atmosphere.
		The planetesimal, descending vertically, would have produced pressure waves that would have begun to arrive, as a sustained roar, immediately after the impact and would have continued to arrive for as many seconds as the body had taken in its journey through the atmosphere.
		The planetesimal, then, would have encountered water that was not warned of its approach and so behaved in a somewhat solid manner, and then to compound the body's misfortunes it would have belly flopped into it.
	www.newearth.demon.co.uk /misc/barrel.htm (5891 words)

	Is Eros An Ancient Planetesimal From Sol's Birth
		Is Eros An Ancient Planetesimal From Sol's Birth
		Planetesimals came to be when the solar system was just a swirling interstellar cloud, slowly collapsing to form the Sun and planets.
		These were planetesimals -- the fundamental building blocks of the planets.
	www.spacedaily.com /news/early-sol-01b.html (1099 words)

	Zoe Malka Leinhardt (Site not responding. Last check: 2007-10-20)
		The largest gap in our understanding of planet formation is planetesimal formation: the method by which small cm-sized particles grow into km-sized objects.
		In general it is believed that planetesimals serve as the planetary building blocks for planets.
		In an attempt to determine the dominant method of planetesimal formation I am conducting a series of direct numerical simulations to parameterize the growth of dust grains into planetesimals as a function of strength, material properties, and physical structure of dust aggregates.
	www.people.fas.harvard.edu /~zmleinh/research/planetesimal.html (165 words)

	Anupadaka: 1 of 2 (87 of 103)
		Full consideration is given to the planetesimal hypothesis of Chamberlin and Moulton and to the modifications of that hypothesis which have been proposed by Jeffreys and Jeans.
		It applies, however, only to an earth constructed according to the planetesimal program; it is utterly ineffective in an earth which has solidified from a molten state.
		Under the planetesimal theory, he explains, this is accounted for by selective ingathering, transportation, and deposition of different sorts of meteoric materials.
	www.wisdomworld.org /additional/ScienceAndTheSecretDoctrine/SeriesNumber87-of-103.html (2262 words)

	World Almanac for Kids
		Before the modern age of space exploration, scientists had three major theories for the origin of the moon: fission from the earth; formation in earth orbit; and formation far from earth.
		The modern version of this theory proposes that the moon was spun off from the earth when the earth was young and rotating rapidly on its axis.
		The catastrophic impact blasted portions of the earth and the planetesimal into earth orbit, where debris from the impact eventually coalesced to form the moon.
	www.worldalmanacforkids.com /explore/space/moon.html (1886 words)

	The Moon (Site not responding. Last check: 2007-10-20)
		As mentioned during the lecture on the origins of the Solar System, toward the end of the collision period the sizes of the planetesimals were large enough to cause some pretty big impacts (knocking Uranus and Pluto on their side, flipping Venus upside down).
		In the Collisional Ejection Theory, during this period the Earth was struck by a Mars-sized planetesimal (Mars is 9 times the mass of the Moon, 1/9th the mass of the Earth) having a rocky mantle over an iron core.
		Computer simulations suggest that the iron core of the planetesimal sank to the center of the Earth while the rocky mantle of the planetesimal was ejected into space, where it accreted and cooled to form the Moon.
	www-astronomy.mps.ohio-state.edu /~monier/Ast161/Unit4/moon.html (808 words)

	[9.10] Stochastic Migration in Planetesimal Disks (Site not responding. Last check: 2007-10-20)
		A residual planetesimal disk of mass \sim10--100 M_\oplus likely remained in the outer solar system following the formation of the giant planets, as suggested by the existence of the Oort cloud, formation requirements for Pluto, and inefficiencies in planet formation.
		The degree of stochasticity depends not only on the number densities of planetesimals, but also on how their orbital semi-major axes and eccentricities are distributed.
		To maintain the viability of resonance capture, planetesimals must be sufficiently small; we apply our theory to estimate the maximum planetesimal size compatible with resonance capture by a migrating Neptune.
	www.aas.org /publications/baas/v37n4/aas207/1909.htm (187 words)

	[No title]
		Chondrule formation in planetesimal bow shocks: Physical processes in the near vicinity of the planetesimal.
		Gravitational instability and clustering in a disk of planetesimals.
		Dust to planetesimals: Settling and coagulation in the solar nebula.
	www.psi.edu /staff/sjw05.pubs (1338 words)

	chapter 12
		) indicate that the planetesimal model is useful for the explanation of the rotation of planets.
		One of these is that, if planets are accreting by capturing grains moving in elliptic orbits in their neighborhood, one can calculate how long a time is needed before most of the grains are accreted to a planet or satellite.
		The change in the proportion of dense materials from that in the accreting planetesimals is thus mainly a secondary effect of the displacement of the light component.
	history.nasa.gov /SP-345/ch12.htm (4445 words)

	Planetesimal
		Planetesimals are thought to form from the coalescing (due to collisional sticking and gravity) of particles, orbiting within the accretion disc of the solar nebula; an accumulation of planetesimals leads to the formation of a protoplanetary disc, which in turn coalesce into protoplanets/planets.
		It is generally argued that by about 3.8 billion years ago most of the planetesimals, within the solar system had either left orbit or coalesced into larger objects.
		The giant impact theory proposes that Earth's Moon formed from a colossal impact of a planetesimal named Theia with Earth early in the solar system's history.
	www.askfactmaster.com /Planetesimal (168 words)

	Quasi-Satellites
		On the left is a sun-centered reference frame rotating with the mean motion of the protoplanet.
		The protoplanet and planetesimal are on eccentric orbits and move faster than the mean motion when nearer to the sun and slower than the mean motion when farther from the sun.
		This gas drag allowed the planetesimal to become trapped in 1:1 mean-motion resonance with the protoplanet --- the planet and the planetesimal both orbit the sun with the same period.
	www.psi.edu /~kortenka/quasi_satellites/quasi_satellites.html (521 words)

	PSR Discoveries: Lessons from the Moon (Site not responding. Last check: 2007-10-20)
		This frame from a computer simulation captures a moment in time when a wandering planetesimal the size of Mars struck the young Earth (shown as the large circle of colorful dots) to form the Moon.
		In this hypothesis, both the planetesimal and Earth already had formed cores (shown in blue-green).
		Computer simulations of such an impact indicate that the core of the planetesimal is added to Earth's iron core and much of the rocky mantles (orange and gold) of the two bodies melts or vaporizes, and some ends up in orbit around the Earth.
	www.psrd.hawaii.edu /Jan97/MoonLessons.html (280 words)

	Notes: THE MOON
		During the last stages of planet formation, planetesimals had grown to be quite large, and their collisions with planets were not gentle.
		During the collision, vast amounts of energy were released, melting both the Earth and the colliding planetesimal.
		The iron core of the colliding planetesimal sank to the center of the Earth and merged with the Earth's core.
	users.zoominternet.net /~matto/M.C.A.S/notes_the_moon.htm (1235 words)

	Chamberlin-Moulton planetesimal hypothesis
		The outer parts expanded and cooled into a huge swarm of solid particles spread out in a disk rotating about the Sun in a plane determined by the motion of the passing star.
		The cores gradually grew into planets by gathering in the planetesimals, most of the growth taking place in the outer parts of the Solar System where material was more plentiful.
		Eventually it became clear that, like other variants of the encounter idea, not enough angular momentum could be conveyed to the ejected material to explain the state of the Solar System as it exists today.
	www.daviddarling.info /encyclopedia/C/CMplanhypoth.html (273 words)

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