Researchers are testing how life on the International Space Station affects the microbiome.

When astronauts on the International Space Station need to go number two, they direct their poo through a narrow hole into a carefully sealed toilet. Eventually, their waste bursts into flames when jettisoned into Earth’s atmosphere.

The fate of the feces of 20 mice tagging along on the ISS this year won’t be quite as flashy, but it’s just as dramatic. The rodents, who shot into space on June 29, made a voyage to the station to provide scientists data on the effects of microgravity on their bodies and internal rhythms—part of which will be captured in their poop.

This mouse madness has a laundry list of questions to answer. Led by principal investigators Fred Turek and Martha Vitaterna of Northwestern University at Evanston, Illinois, researchers at multiple institutions will examine how microgravity affects (or disrupts) the animals’ gut microbiome, gastrointestinal function, immune function, metabolism, and sleep and circadian rhythms.