Earlier today, SpaceX’s Dragon cargo spacecraft plopped into the Pacific Ocean after spending a few weeks on the International Space Station (ISS).

The spacecraft is carrying 31,000 pounds worth of cargo from the ISS, NASA reports, including experiments that scientists will examine here on Earth. This round of experiments focused on how spaceflight affects aging, bone density, metabolism, muscle mass and more. The results will help NASA determine how longer space flights—say, to Mars—will affect astronauts.

The subjects, and stars, of these studies are ISS-lab-grown worms. Per NASA:

“The returning Space Aging study, for example, examines the effects of spaceflight on the aging of roundworms, widely used as a model for larger organisms. By growing millimeter-long roundworms on the space station, researchers can observe physiological changes that may affect the rate at which organisms age.”

Caenorhabditis elegan. Image via NASA

Another study also featured the roundworms. Again, NASA explains:

“Some astronauts experience weakened muscles, reduced bone density and changes in metabolism, so researchers are using the roundworms as models to try to clarify how and why these changes take place in microgravity.”

Thank you for your service, worms, we salute you.

Danielle Wiener-Bronner is a news reporter.