https://www.lpl.arizona.edu/~renu/malhotra_preprints/1999-sciam.pdf
At distances of less than 0.5 AU from a star,there is insufficient mass in the primordial disk for solid protoplanetary coresto condense. Furthermore, it is questionable whether a protoplanet in a closeorbit could attract enough ambient gas to provide the massive envelope of aJupiter-like planet. One reason is simple geometry: an object in a tight orbittravels through a smaller volume of space than one in a large orbit does. Also,the gas disk is hotter close to the star and hence less likely to condense ontoa protoplanetary core. These considerations have argued against the formationof giant planets in very short-period orbits.
The third mechanism is the scattering of large planets that either formed in or moved into orbits too close to one another for long-term stability. In this process, the outcomes would be quite unpredictable but generally would yield very eccentric orbits for both planets. In some fortuitous cases, one of the scattered planets would move to an eccentric orbit that would come so near the star at its closest approach that tidal friction would eventually circularize its orbit; the other planet, meanwhile, would be scattered to a distant eccentric orbit. All the mechanisms accommodate a broad range of final orbital radii and orbital eccentricities for the surviving planets
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发表于 2018-6-28 19:43:42
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