Popular Solar System Orbits

Protoplanetary Disk
Protoplanetary Disk Swept of Dust 1-2 AU from the Star
Image Credit: NASA / JPL-Caltech

Ilaria Pascucci at the University of Arizona’s Lunar and Planetary Laboratory and Richard Alexander of the University of Leicester in the United Kingdom, presented evidence at the 43rd Lunar and Planetary Science Conference in The Woodlands, Texas, that gaps in protoplanetary disks are carved out by high energy radiation from very young stars, and these gaps are barriers to planets shifting orbits during their formation.

The process discussed at the conference is photo-evaporation. Close to the star, material in the disk is held tightly by the strong gravitational pull of the star, preventing the high energy radiation from the young star from dispersing the disk. Farther out, in the range of 1 to 2 Astronomical Units (AU – the distance from the Sun to the Earth), the radiation is strong enough heat the gas in the disk, but gravity is less strong and the gas evaporates into space leaving a “desert”. Even farther out, it is too cold for the gas and dust to evaporate.

Observations of solar systems show that giant planets migrate inward during formation, drawn along by the disk material accreting into the young star. However, the new computer simulations show that the migration ceases at the void or gap in the protoplanetary disk. This leads to a pileup of planets on either side of the gap. Pasucci noted that:

The planets either stop right before or behind the gap, creating a pile-up. The local concentration of planets leaves behind regions elsewhere in the disk that are devoid of any planets. This uneven distribution is exactly what we see in many newly discovered solar systems.

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