Answer:
The sentence from the article "Can Mars Be Made Hospitable to Humans?" that can serve as a central theme is: "A green Mars is better than a red Mars".
This basically captures the subject matter/objective as far as Mars is concerned.
Step-by-step explanation:
If Mars were made greener, it means that it would have more plants. More plants mean more oxygen. More oxygen means more ability to support a greater diversity of life.
Cheers!