We can also use might, may and could for talking about what we think was possible in the past. NASA says it may/might/could have been suitable for life in the past. We use the modal verbs must and ...

Modal verbs: Might, may, could, must and can’t Meaning and use We can use the modal verbs might, may, could, must and can’t for talking about what we think is possible ... Might, may, could ...