I found this question on Quora.
Here’s my answer:
A human child born in any place not within the Earth’s atmosphere would correctly be classified as an extraterrestrial. It would still be a human.
Extra means “outside” and terrestrial means “of Earth”.
If there were a word for beings that did not originate on Mars, that word would also apply to them.
The word “alien” would apply in both cases.
No amount of words would change the fact that the baby was born from the combination of human DNA in the usual fashion. (Unless of course, it wasn’t formed that way. You didn’t specify that in your question.)
Words are just words.