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A Planetary Migration?

With the Kepler launch scheduled for no earlier than Friday, I’m keeping one eye on the mission site while I develop today’s material. Kepler launches aboard a Delta II, but engineers are now having to check common hardware between that rocket and the Taurus XL launch vehicle that failed to get NASA’s Orbiting Carbon Observatory into orbit last week. Thus the March 5 launch date slips to March 6, which itself is still tentative.

Meanwhile, an unusually interesting story in Nature also has my attention, dealing not with exoplanets but with the early Solar System and what may have been a period of planet migration that caused heavy asteroidal bombardment of the inner planets. This one comes out of the University of Arizona, where scientists have been looking at the distribution of asteroids with diameters greater than fifty kilometers. UA’s David Minton and Renu Malhotra ran simulations beginning with a uniform asteroid belt to see how the present-day gaps in the belt may have arisen over time.

At issue are the so-called Kirkwood gaps, which occur in areas where gravitational effects from both Jupiter and Saturn perturb the belt and eject asteroids. The result of the simulations: Areas exist where asteroid orbits are stable but no asteroids exist. But if the effects of giant planet migration in the early system are added to the mix, the simulated belt matches up well to what we see today. Those extra areas of asteroid depletion, then, may be the signature of planetary migration. Says Malhotra:

“Our interpretation is that as Jupiter and Saturn migrated, their orbital resonances swept through the asteroid belt, ejecting many more asteroids than is possible with the planets in their current orbits. And the particular pattern of missing asteroids is characteristic of the pattern of Jupiter’s and Saturn’s migration.”

Thus we have evidence that the giant planets formed with closer spacing than in today’s Solar System, with Jupiter then moving slightly closer to the Sun, while Saturn, Uranus and Neptune moved farther from the Sun and from each other. These events would have been destabilizing enough for the asteroid belt that the possibility of linking them to early, heavy bombardment of the inner planets is worthy of further study.

Graduate student Minton and planetary sciences professor Malhotra seem to make a good team — you may also want to have a look at their recent study of the extrasolar system OGLE-2006-BLG-109L, which examines a possible system architecture that includes the two detected massive planets and has the potential for two terrestrial-class worlds which, if they exist, could create an environment that mimics our Solar System. That paper is “Prospects for the Habitability of OGLE‐2006‐BLG‐109L,” Astrophysical Journal Letters 683 (August 10, 2008), pp. L-67-70 (abstract). The asteroid paper is “A record of planet migration in the main asteroid belt,” Nature 457 (February 26, 2009), pp. 1109-1111 (abstract).

Comments on this entry are closed.

  • Didac March 2, 2009, 15:57

    A very interesting research indeed. It is evident that a description of any planetary system needs to address the question of the orbital evolution of planets. Anyhow, this method seems far more reliable than Velikovsky’s ;)

  • ljk March 13, 2009, 17:22

    Life could have survived Earth’s early pounding

    15:19 10 March 2009 by Jeff Hecht

    Microbes living deep underground could have survived the massive barrage of impacts that blasted the Earth 3.9 billion years ago, according to a new analysis.

    That means that today’s life might be descended from microbes that arose as far back as 4.4 billion years ago, when the oceans formed.

    Around 3.9 billion years ago, shifts in the orbits of the gas giant planets are thought to have disrupted other objects in the solar system, sending many hurtling into the inner planets. Geologists call that time the Hadean Eon, and thought its fiery hell of impacts would have sterilised the Earth.

    But a new study by Oleg Abramov and Steve Mojzsis of the University of Colorado in Boulder suggests hardy life-forms could have survived if they were buried underground. They will report the results on 23 March at the Lunar and Planetary Science Conference in Texas.

    Full article here:


  • ljk August 13, 2009, 10:49

    Neptune migration model with one extra planet

    Authors: Lun-Wen Yeh, Hsiang-Kuang Chang

    (Submitted on 12 Aug 2009)

    Abstract: We explore conventional Neptune migration model with one additional planet of mass at 0.1-2.0 Me. This planet inhabited in the 3:2 mean motion resonance with Neptune during planet migration epoch, and then escaped from the Kuiper belt when Jovian planets parked near the present orbits.

    Adding this extra planet and assuming the primordial disk truncated at about 45 AU in the conventional Neptune migration model, it is able to explain the complex structure of the observed Kuiper belt better than the usual Neptune migration model did in several respects.

    However, numerical experiments imply that this model is a low-probability event. In addition to the low probability, two features produced by this model may be inconsistent with the observations. They are small number of low-inclination particles in the classical belt, and the production of a remnant population with near-circular and low-inclination orbit within a = 50-52 AU.

    According to our present study, including one extra planet in the conventional Neptune migration model as the scenario we explored here may be unsuitable because of the low probability, and the two drawbacks mentioned above, although this model can explain better several features which is hard to produce by the conventional Neptune migration model.

    The issues of low-probability event and the lack of low-inclination KBOs in the classical belt are interesting and may be studied further under a more realistic consideration.

    Comments: 42 pages, 12 figures

    Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

    DOI: 10.1016/j.icarus.2009.06.008

    Cite as: arXiv:0908.1729v1 [astro-ph.EP]

    Submission history

    From: Lun-Wen Yeh [view email]

    [v1] Wed, 12 Aug 2009 15:15:33 GMT (663kb)