SpaceX gets a lot of press for its rocket ship launches and landings. We’ve seen the Falcon 9 explode in extraordinary spectacles. We’ve seen a rocket overcome intimidating odds. We don’t, however, hear about SpaceX’s spacecraft, the Dragon, nearly as often. While the Falcon 9 rocket ships perform quick missions to deliver payload into orbit, Dragon cargo spacecraft take long journeys into space and take some time to return to Earth.

Well, the Dragon did return to Earth on Wednesday and brought with it “critical NASA science,” according to the space agency. The 3,000 pound commercial resupply spacecraft made a splash in the Pacific Ocean just before 3 p.m. EDT packed with 3,700 pounds of valuable scientific data transported from the International Space Station.

Space provides scientists an environment where they can perform experiments not possible on Earth. The space station’s microgravity, for example, can offer unique insight into how particles, bodies, and organisms behave in space. NASA describes one nanotechnology study to test how microparticles interact when not burdened by the standard force of Earth’s gravity.

But sometimes these experiments study the effects of a microgravity environment on astronauts themselves. Identical-twin astronauts Scott and Mark Kelly engaged in a nearly yearlong study to test how the human body adapts to microgravity environments.

While Mark spent a year on Earth, Scott spent a year in space. When Scott returned to Earth in February 2016, he left behind human research samples at the International Space Station. When the Dragon returned home yesterday, part of its cargo included Kelly’s leftover data, which NASA hopes to analyze and apply to the agency’s Journey to Mars in the 2030s.

SpaceX, meanwhile, may not have the twin experiment scientific data, but has planned its own trip to Mars, with an ambitious deadline of 2018.