Question

Within the disc of gas and dust that surrounded the protoSun there was a radial temperature gradient outwards to the edge of the disc. Describe the sequence of events that led to the beginning of planet formation (i.e. when planetary embryos were colliding). and the effect the temperature gradient had on this process. (About 150 words)

Answer 1

Answer:

The sequence of events that led to the beginning of planet formation:

Step I:From dust to planetesimals:

When a molecular cloud collapsed under its own gravity to form a star, the material formed a disk-like structure in orbit around the central object, due to the conservation of angular momentum.

Planetesimals formed due to the collective gravity of massive swarms of small particles, concentrated at some locations (local maxima of the gas density distribution or inter-vortex regions, depending on particle sizes) by the turbulence of the disk.

Step II: from planetesimals to planetary embryos

Once the proto-planetary disk contained a substantial population of planetesimals and the dynamics of accretion became dominated by the effect of the gravitational attraction between pairs of planetesimals, the second stage of planet formation started.

During this phase of accretion -- runaway growth, -- big bodies grew faster than the small ones and hence rapidly increased their relative mass difference.

Step III: from embryos to terrestrial planets

At the time of the disappearance of the gas from the proto-planetary disk, the solar system had the following structure: (i) in the inner part, a disk of planetesimals and planetary embryos with roughly equal total mass in each component; (ii) in the central part, a fully-formed system of giant planets; and (iii) beyond the orbits of the giant planets, another disk of planetesimals.

The effect the temperature gradient had on this process:

1. When the temperature in the disk decreased with distance from the Sun, a classic condensation sequence characterized by a clear radial gradient of chemical properties was obtained.

2.There are three classes of chondritic meteorites: enstatite, ordinary and carbonaceous. Their chemistry and mineralogy suggest that these three classes formed respectively at decreasing temperatures. For instance, water is essentially absent on enstatite meteorites, and quite abundant in (some subclasses of) carbonaceous chondrites, while the water-content in ordinary chondrites is intermediate between the two.

3.Radial gradient in temperature existed in the disk at the time(s) when planetesimals formed. In particular, planetesimals in the inner disk (in the inner asteroid belt region and presumably also in the terrestrial planet region) were dry and volatile poor.

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