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Posted on 09/19/2009 8:11:04 AM PDT by SunkenCiv
...In most models, it's a three-step process: (1) dust settles into a flattened disk and collects into countless planetesimals a mile or so (1 to 10 km) across; (2) the planetesimals collide and form Moon- to Mars-size planetary embryos; and (3) the embryos smash into one another until basically all that remains are a handful of rocky inner planets and a second handful of rocky "super-Earth" cores that eventually become the giant outer planets. In other words, the solar system's building blocks grew smoothly and systematically from small bodies to large ones.
But recent studies have (forgive me) punched huge holes in this traditional thinking. For one thing, there's no obvious way for Mother Nature to have assembled objects larger than about 1 meter across within the disk -- the forces at play would have caused such bodies to smash themselves to bits or to spiral rapidly into the Sun. Fortunately, work in 2007 and 2008 by theorists Anders Johansen and Jeffrey Cuzzi (and their respective teams) suggests that really big planetesimals could have formed directly from pebble-size particles, bypassing the need for intermediate sizes and neatly sidestepping the "meter-size barrier."
Now a quartet of well-known dynamicists led by Alessandro Morbidelli (Côte d'Azur Observatory, France) has concluded that the Johansen and Cuzzi teams probably got it right. In particular, they find, the asteroid belt wouldn't have the assortment of big and small objects we see today (known as its size-frequency distribution, or SFD) if it initially teemed with smallish planetesimals. Instead, they argue, most of the original inhabitants would have been closer to the size of Ceres, the modern-day belt's undisputed king.
(Excerpt) Read more at skyandtelescope.com ...
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ML/NJ
Sure, but back then miles were longer. ;’)
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