I'm guessing maybe the earlier people has emergency shelter or helpful stuff that is hidden somewhere in the controls in case of the current underground world nearing its end of life.
@Glomoro yeah, but these are the only 2 humans trying to help earth. They wouldn't tell them to do anything risky that could cause them to die before they finish helping earth unless it was needed. So they would've been sure it was safe before telling her to take it off, not just on a whim.