From RealClearScience:
The pebble accretion model, as the idea is called, suggests that tiny objects first coalesce together due to drag then gravitationally collapse and form larger objects one hundred to one thousand kilometers in size. These larger objects, now referred to as planetesimals, than draw in all the remaining pebbles and become the cores of larger planets.
Simulations completed last year cast doubt on this interesting theory. They suggested that — in the context of our solar system — too many planetesimals would form — as many as one hundred objects the size of Earth! Since our Solar System only contains eight planets and five recognized dwarf planets, this theory was mostly ruled out.
However, a new simulation carried out primarily by researchers at the Southwest Research Institute and published to the journal Nature suggests that if these pebbles form slowly enough, fewer large planetesimals will emerge. More.
Well, if such contradictory theories (gas vs. pebbles) are both in play, it sure isn’t a time for dogma.
See also: “Behold, countless Earths sail the galaxies … that is, if you would only believe …”
Don’t let Mars fool you. Those exoplanets teem with life!
and
How do we grapple with the idea that ET might not be out there?
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