Talk:Pebble accretion

Aerodynamic drag forming large rocks in outer space from pebbles?

Outer space is vacuum, how exactly do pebbles clump together from aerodynamic drag when outer space is hard vacuum? Aerodynamics requires air, and air is held in place by an object with a pre-existing large gravitational field. Seems they just made this up without any thought. Trilliant (talk) 21:04, 20 November 2016 (UTC)[reply]

Because the protoplanetary disk isn't "outer space" - it's full of dust and gas and pebbles. Primefac (talk) 02:24, 20 January 2017 (UTC)[reply]

If you took all the material of all the solar system objects, broke it all up into gas and dust, the area would still be a strong vacuum given it was spread out to the orbit of any object orbiting the Sun. I do not think scientists understand what they are doing or the scale of the solar system. The space in between the objects is too vast to have formed from a single disk. This means the idea of pressure existing in any disk is bunk. There would not be any pressure at all, you would need material from thousands of Sun's to give just a tiny bit of pressure for a disk out to the orbit of Neptune. Not only that but the gas would dissipate given it could even form in a disk orientation, because there is not anything to prevent gas loss back into space. What is being proposed makes as much sense as inflating a basketball that has two holes in it. Trilliant (talk) 19:44, 6 May 2017 (UTC)[reply]

The pebbles have a long time to decelerate as they pass by objects. For example the Bondi time (roughly how much time it has to be slowed) for an object the mass of Vesta is 1.6 days. It wouldn't take a very dense medium to slow a marble-sized object enough for it to be captured and accreted. Agmartin (talk) 20:52, 21 January 2017 (UTC)[reply]