Planetesimals /plænɪˈtɛsɪməlz/ are solid objects thought to exist in protoplanetary disks and debris disks

. Per the Chamberlin–Moulton planetesimal hypothesis, they are believed to form out of cosmic dust grains. Believed to have formed in the solar system about 4.6 billion years ago, they aid study of its formation.

What was the planetesimal era?

Oldest rock on Earth. dated back to 4.28 billion years ago. Planetesimal theory. was put forth by Viktor Safronov in 1941; the theory explained planet formation in the early solar system from accretion of small bodies, growing in size as gravity attracted more and more objects.

How was planetesimal formed?

Planetesimals formed in the solar nebula by collisional coagulation. Dust aggregates settled toward the central plane, the larger ones growing by sweeping up smaller ones.