Tideglass Studio
The eight stages

Stage 2 of 8

Pebble

Gains: Accretion

Now the field comes to you. Sweep up pebbles and grow fast.

Past the frost line, ice glues dust into pebbles, and pebbles fall onto you like a slow rain.

Frost-coated dust grains beyond the frost line of a protoplanetary disk.

Crossing the frost line

Far enough from the young star, it grew cold enough for water to freeze onto dust. Ice is sticky. Where bare grains only bounced, frosted ones clung and held. You crossed that line and began to gather frosted dust faster than ever, a snowball rolling through a snowfield that never ends.

A small rocky body sweeping up a stream of pebbles in a gaseous disk.

A rain of pebbles

The disk's gas blew a gentle, constant headwind, and it nudged a steady stream of pebbles your way. This is pebble accretion, and it is shockingly efficient. You did not have to chase anything. You simply held your place, and the universe delivered itself onto your back, one small stone at a time.

True things

  • Pebble accretion lets bodies grow millions of times faster than by catching one grain at a time.
  • The frost line is the distance from a star where it is cold enough for water ice to form.
  • Comets are leftover icy pebble-piles that never finished becoming planets.