Human missions to Mars will require a substantial launch vehicle to ascend from Mars to rendezvous with a waiting Earth return vehicle in Mars orbit. For an ascending crew of 6, the current best estimate of oxygen propellants required for ascent is about 30 metric tons. Producing oxygen for ascent propellants and possibly life support from the indigenous CO2 on Mars, rather than bringing oxygen to Mars from Earth, is of significant benefit.
Click here for original story, Scientists propose adapting a Mars ISRU system to the changing Mars environment
Source: Phys.org