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Jupiter and Saturn - Back and Forth in the Early Solar System?

  1. Oct 16, 2012 #1
    The Extrasolar Planets Encyclopaedia
    Exoplanet Orbit Database | Exoplanet Data Explorer
    Numerous planets outside the Solar System have been discovered, and for some curious reason, a large number of them are around Jupiter's mass, but much closer in than one would expect. The usual theory nowadays is that they formed at a larger distance, then spiraled in as a result of their interaction with the still-remaining protoplanetary nebula.

    But what happens to the inner planets? Would they still form?
    [1004.0971] The Compositional Diversity of Extrasolar Terrestrial Planets: I. In-Situ Simulations -- no migration
    [1209.5125] The Compositional Diversity of Extrasolar Terrestrial Planets: II. Migration Simulations

    Apparently, they can, at least if not too close to one of these wandering giants. However, their composition tends to be more mixed, because of the giants' mixing up the protoplanetary nebula, and Earthlike planets can get much more water than the Earth has, making much deeper oceans.

    But if wandering giant planets are so common, then why is it that the Solar System's ones did not migrate? Or did they?

    Some planetary scientists are proposing that Jupiter and Saturn spiraled in, then spiraled out again.

    Full text here
    How Did Jupiter Shape Our Solar System?
    NASA - Jupiter's Youthful Travels Redefined Solar System
    Here's a nice presentation: The Grand Tack Hypothesis, after a sailing maneuver

    In it, Jupiter starts out at 3.5 AU, Saturn at 4.5 AU, Uranus at 6 AU, and Neptune at 8 AU. Jupiter spirals in to about 1.5 AU in 100 thousand years (kyr), Saturn quickly follows at about 100 kyr, while Uranus and Neptune don't move very much.

    Along with the giant planets are lots of planetesimals, small asteroid-like objects that condensed out of the solar nebula. From 0.3 to 3 AU are S-type (stony) ones, and from 3.5 to 13 AU are C-type (carbonaceous-chondrite) ones. The C-type ones contain water, from where they formed.

    Jupiter and Saturn push the S-type objects together, while mixing up S-type and C-type ones as they go. Some S-type ones end up in the outer Solar System, while some C-type ones end up in the inner Solar System.

    Then Jupiter and Saturn get locked in a 3:2 resonance, with Jupiter at 1.5 AU and Saturn at 2 AU, and their interactions with the protoplanetary disk push them outward. As they go outward, they push Uranus and Neptune outward as those planets get into resonances with them. They also leave behind the asteroid belt as they go.

    Inside 3.5 AU, it's mostly S-type asteroids, while outside 3.5 AU, it's mostly C-type asteroids.

    Mars ends up relatively small, since it does not have as much starting material as the Earth.

    The C-type planetesimals supply water to the inner planets, making the Earth's oceans.

    It's also a good setup for the Nice model of outer-planet migration. Saturn, Uranus, and Neptune keep going further out, and they scatter lots of planetesimals outward to form the Kuiper Belt. The Nice here is not the English word, but Nice, France, where the model was developed.

    The origin of the giant planets is still not very well understood, it must be said.

    For some somewhat technical background on planetary-system formation, check out Scott Tremaine's home page
    Last edited by a moderator: May 6, 2017
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  3. Oct 16, 2012 #2

    D H

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    There's a problem with this jumpin' Jupiter hypothesis: When simulated, one of the outer gas giants tend to get expelled. A recent competing hypothesis that claims to overcome this problem is that a gas giant was expelled: A fifth gas giant.

    David Nesvorný, "Young Solar System's Fifth Giant Planet?", 2011 ApJ 742 doi:10.1088/2041-8205/742/2/L22
  4. Oct 16, 2012 #3
    That's interesting. Close encounters could also explain the sizable number of exoplanets in very eccentric orbits.

    Using the data in exoplanets.org, about 1/3 of all known exoplanets have orbit eccentricities > 0.2, and 1/2 with e's > 0.1.

    The very close ones tend to have nearly circular orbits, however. It's those with a major axis of 1 - 3 AU's that often have large eccentricities.
  5. Oct 16, 2012 #4


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    Well, statistics based on known exoplanets are tricky - you always have selection effects. For the same major axis, a larger eccentricity leads to larger differences in the radial velocity of the star, for example. I would expect that it increases the transit probability, too. The effects might be of second order (?), but they are there. And most exoplanets were found with those two methods.
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