Pinti, Michel Viso. Contents Search. Planetary Migration. Authors Authors and affiliations Avi M. How to cite. This is a preview of subscription content, log in to check access. The relevant coefficient of diffusion would determine the rate of the movement of ink in the water.
Chaos in this context refers to the irregular behavior in the orbital evolution of objects asteroids, comets, and interplanetary dust in the Solar System [2]. Chaotic diffusion causes dispersion of Trojan asteroids — asteroids orbiting our Sun from the same distance as Jupiter [3]. According to the diffusion coefficient I obtained, it takes about , years for an average low-mass object to diffuse approximately 60 astronomical units AU , where 1 AU is the distance between Earth and the Sun.
In this time a low-mass object can grow larger by accreting matter. This way once planets are born, they can move away and evolve. Therefore, solar systems evolve and change! Having a better understanding of the diffusion of objects during the early evolution of a planetary system helps us to understand the architecture of planetary systems, the diversity of exoplanets, and the nature of the universe in which we live. Edited by Guillaume J.
Dury and Kerri Donohue. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Are you a graduate student at IUB? Such cosmochemistry evidence is becoming increasingly important, and provides a growing number of constraints on the formation of the early Solar System. Planets typically acquire mass from a range of distances within a protoplanetary disk, although the mixture is different for each object, leading to a unique chemical composition.
It is likely that Earth acquired most of its water and other volatile materials from relatively cold regions of the Sun's protoplanetary disk such as the asteroid belt. Simulations of terrestrial-planet formation are able to reproduce the basic architecture a small number of terrestrial planets with low-eccentricity orbits of the inner Solar System from plausible initial conditions. The stochastic nature of planetary accretion, however, means that a precision comparison between the Solar System and theoretical models in not possible.
The number and masses of terrestrial planets are predicted to vary from one planetary system to another due to differences in the amount of solid material available and the presence or absence of giant planets, as well as the highly stochastic nature of planet formation.
The presence of a giant planet probably frustrates terrestrial-planet formation in neighboring regions of the disk, leading to the absence of terrestrial planets in these regions or the formation of an asteroid belt.
These predictions will be tested by ongoing and future space missions designed to search for extrasolar terrestrial planets, such as COROT and Kepler.
Giant planets are qualitatively distinct from terrestrial planets in that they possess significant gaseous envelopes. In the Solar System, the gas giants Jupiter and Saturn are predominantly composed of hydrogen and helium gas, although these planets are enriched in elements heavier than helium compared to the Sun. The ice giants Uranus and Neptune have lesser, but still substantial several Earth masses gas envelopes. The existence of these envelopes provides a critical constraint: giant planets must form relatively quickly, before the gas in the protoplanetary disk is dissipated.
Observations of protoplanetary disks around stars in young clusters pin the gas-disk lifetime in the million year range. The standard theory for the formation of gas giants, core accretion , is a two-stage process whose first stage closely resembles the formation of terrestrial planets.
A core with a mass of the order of 10 Earth masses forms in the disk by numerous collisions between planetesimals. Typically, there is not enough solid material to form bodies this massive in the inner region of a protoplanetary disk. At larger orbital radii, beyond the snow line , the temperature is low enough that ices as well as rocky materials can condense. This extra solid material, together with the reduced gravity of the central star, allows large solid cores to form in the outer regions of a disk.
Initially a core is surrounded by a low-mass atmosphere, which grows steadily more massive as the gas cools and contracts onto the core. Eventually the core exceeds a "critical core mass", beyond which a hydrostatic envelope cannot be maintained. Determining an accurate time scale for reaching the critical core mass is very difficult, in part because the rate at which the gas cools depends upon how transparent the envelope is.
The transparency varies dramatically with the amount of dust present, which is extremely uncertain. Once the core mass is exceeded, gas begins to flow onto the core. It is slow at first but increases rapidly as the planet becomes more massive. Growth ceases when the supply of gas is terminated, either because the planet opens a gap in the disk or because the disk gas dissipates.
A second theory for gas-giant formation, gravitational disk instability , also remains under study. If, additionally, the disk is able to cool on an orbital timescale, then the instability leads to fragmentation of the disk into bound objects.
In protoplanetary disks, these objects would have masses comparable to giant planets. A key feature of this mechanism for forming giant planets is that it works extremely rapidly. Unlike core accretion, solids play no direct role in the process. Core accretion is generally considered to be a more plausible model for giant-planet formation than gravitational instability for several reasons.
First, theoretical calculations suggest that although young protoplanetary disks may be massive enough to be unstable, they are unlikely to cool rapidly enough to fragment except perhaps at very large radius. Secondly, the core-accretion model naturally explains the existence of ice-giant planets like Neptune although the time scale for formation of the ice giants is worryingly long if they formed at their present locations.
This reordering is referred to by scientists as planetary migration. Artist impression of an accretion disk. There are three ways in which planetary migration is understood to occur: the first describes a gas driven process in which the planetary disk effectively pushes or pulls the planet to a new position; the second arises as a result of gravitational interactions between neighbouring bodies, where a large object can scatter a smaller one and thereby create an equal and opposite resulting force back onto itself; and the third is due to another gravitational effect, tidal forces, which mainly occur between the star and the planet and tend to result in more circular orbits.
Surprising as it may seem to some, it is widely accepted that planetary migration has shaped and influenced the architecture of the Solar System quite dramatically.
In fact, its dynamic past actually explains the existence and properties of several Solar System entities, and shows that our planetary system might not be as unique as once thought. So how have the planets moved since their birth? It all began with the inward migration of the largest planet in the Solar System, Jupiter. The gas giant, weighing more than all the other planets combined, is believed to have travelled right up to the orbit of Mars, 1. Luckily for Mars this occurred some million years into the birth of the Solar System around 4 billion years ago before any of the terrestrial planets had formed and only four gas giants ruled the skies.
At this time, Jupiter, Saturn, Uranus and Neptune possessed much more compact orbits and were surrounded by a dense disk of small icy objects. Artist impression of planetary system. Jupiter was drawn towards the Sun by the first type of planetary migration, gas driven, whose effects work differently depending on the mass of the planet.
If angular momentum is lost the planet migrates inwards, and if it is gained it travels outwards. This is known as Type I migration and occurs on a short timescale relative to the lifetime of the accretion disk. In the case of high mass planets, like Jupiter, their strong gravitational pull clears a sizeable gap in the disk which ends Type I migration and allows Type II to take over.
Here the material enters the gap and in turn moves the planet and gap inwards over the accretion timescale of the disk. This migration mechanism is thought to explain why hot Jupiters are found in such close proximity to their stars in other planetary systems.
The third type of gas driven migration is sometimes referred to as runaway migration, where large-scale vortices in the disk rapidly draw the planet in towards the star in a few tens of orbits.
The three types of disk migration. This model suggests that at the inner edge of the icy disk, some 35 AU from the Sun, the outermost planet began interacting with icy planetesimals, influencing the second sort of migration to occur: gravitational scattering. Comets were slingshotted from one planet to the next, which gradually caused Uranus, Neptune, Saturn and the belt to migrate outwards. This resulted in the stunted growth of Mars and a material-rich region from which the Earth and Venus formed, explaining their respective sizes.
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