All pure assumption! In your case, however, friend Michael, no comet whatever is necessary.

The shock that gave rise to your great 'star' may have come from the interior rather than the exterior.

A violent contraction of the lunar crust in the process of cooling may have given birth to your gigantic 'star' formation." "I accept the amendment," said Ardan, now in the best of humor and looking triumphantly at M'Nicholl.
"An English scientist," continued Barbican, "Nasmyth by name, is decidedly of your opinion, especially ever since a little experiment of his own has confirmed him in it.

He filled a glass globe with water, hermetically sealed it, and then plunged it into a hot bath.

The enclosed water, expanding at a greater rate than the glass, burst the latter, but, in doing so, it made a vast number of cracks all diverging in every direction from the focus of disruption.