The most common and most likely answer to this crossword clue is the 10 letter word EARTHBOUND
I've seen this crossword clue in The Guardian
E
A
R
T
H
B
O
U
N
D
More clues leading to the result EARTHBOUND
Buddy explains!
The straight part
We know that "Coming to this planet/unable to leave it" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case coming to this planet/unable to leave it = earthbound.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does EARTHBOUND mean?
EARTHBOUND adjective- Confined to the Earth.
- Unimaginative or mundane.
- Heading towards Earth.