how do scientist think the moon was most likely formed?

Question

what is the planetesimal theory of lunar formation

Answer 1

A Planetesimal object forms from a rotating cloud of interstellar gas. So (I don't know for sure) I would assume the planetesimal theory of lunar formation is the idea that the moon formed from the same gas that the Earth was made from. This is not widely accepted.

To answer your first question, the most widely accepted theory is that an object, possibly the size of Mars, impacted the Earth during its early formation, when it was already a sphere but still... soft and mushy, made of lava. This impact separated some surface material from the Earth, from which the moon was formed.

Answer 2

The latest theory is that a mars-sized object hit the earth during its early formation and scattered debris into orbit, which coalesced into the moon.

Answer 3

There are three theories about how the moon came to be:
that the moon came out of the crust of the Earth
that the moon was captured by the Earth
that the Earth and moon formed together out of the primordial nebula