As humanity turns its gaze toward the Moon and Mars, a quiet but consequential question has shadowed every mission plan: can the heart endure the weightlessness that weakens bone and muscle? Researchers from the University of Chicago and University of Nebraska, studying cardiac tissue from mice that spent 38.5 days aboard the International Space Station, found that the heart's contractile machinery remained as strong as that of Earth-bound counterparts. It is a finding that does not resolve every uncertainty, but it offers something rare in the calculus of deep-space exploration — a reason for