NASA says a crew member on the International Space Station is unwell. The agency canceled a planned spacewalk for Thursday and is taking the rare step of ending the Crew-11 mission early.

The International Space Station (ISS) is a closed ecosystem, and the biology inside it — including its microbial residents — don't necessarily behave the same way on our home planet.

All four Crew 11 fliers looked healthy and in good spirits on a space-to-ground television broadcast of the change of command ceremony with no indication of which astronaut may have experienced the undisclosed medical issue that triggered Crew 11's early departure.

Four astronauts are set to depart the International Space Station Wednesday amid a health concern. The unprecedented early departure will leave behind a skeleton crew.

In a new study, terrestrial bacteria-infecting viruses were still able to infect their E. coli hosts in near-weightless "microgravity" conditions aboard the International Space Station, but the dynamics of virus-bacteria interactions differed from those observed on Earth.

SpaceX launched its third mission of the year from the Space Coast on Monday afternoon while preparing for the early return later this week of Crew-11 from the International Space Station.

ISS research over 25 years shows how humans adapt biologically, medically, and technologically to space, informing future missions and scientific understanding of life beyond Earth.