The Perseverance rover has successfully converted carbon dioxide from the Red Planet's atmosphere into oxygen. Eventually, the technology inside the toaster-size Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) unit in Perseverance's belly could support human visits and perhaps even settlements on Mars. From NASA:
While the technology demonstration is just getting started, it could pave the way for science fiction to become science fact – isolating and storing oxygen on Mars to help power rockets that could lift astronauts off the planet's surface. Such devices also might one day provide breathable air for astronauts themselves
To burn its fuel, a rocket must have more oxygen by weight. To get four astronauts off the Martian surface on a future mission would require approximately 15,000 pounds (7 metric tons) of rocket fuel and 55,000 pounds (25 metric tons) of oxygen. In contrast, astronauts living and working on Mars would require far less oxygen to breathe. "The astronauts who spend a year on the surface will maybe use one metric ton between them," Hecht said.
Hauling 25 metric tons of oxygen from Earth to Mars would be an arduous task. Transporting a one-ton oxygen converter – a larger, more powerful descendant of MOXIE that could produce those 25 tons – would be far more economical and practical.
Mars' atmosphere is 96% carbon dioxide. MOXIE works by separating oxygen atoms from carbon dioxide molecules, which are made up of one carbon atom and two oxygen atoms. A waste product, carbon monoxide, is emitted into the Martian atmosphere.
image/caption credit NASA/JPL-Caltech: "Technicians in the clean room are carefully lowering the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) instrument into the belly of the Perseverance rover. The rover has been inverted so that the interior is more accessible. MOXIE will "breathe in" the CO2-rich atmosphere and "breathe out" a small amount of oxygen, to demonstrate a technology that could be critical for future human missions to Mars."