Mars was once an Earth-like world. ... Combined with a thick atmosphere, a magnetic field to shield against radiation, and a variety of organic molecules, Mars had favorable conditions to form and support life as we know it. Mars probably didn't remain habitable for very long, though.

Can we live on Mars?

However, the surface is not hospitable to humans or most known life forms due to the radiation, greatly reduced air pressure, and an atmosphere with only 0.16% oxygen. ... Human survival on Mars would require living in artificial Mars habitats with complex life-support systems.

Why is Mars not currently habitable?

Hazards and difficulties include low gravity, low light levels relative to Earth's, and the lack of a magnetic field. Disagreement exists about whether current technology could render the planet habitable.