Final answer:
Mars is the planet with Olympus Mons and Valley Marineris, having a thin CO2 atmosphere and no magnetic field.
Step-by-step explanation:
The planet that is the home of Olympus Mons and Valley Marineris, and is known for having no magnetic field and a very thin CO2 atmosphere, is Mars.
This red planet rotates in about 24 hours, similar to Earth, and has seasons due to its axial tilt. Unlike the lifeless planet Mercury which has no atmosphere, or Venus with its incredibly thick and hot CO2 atmosphere, Mars retains a thin atmosphere made mostly of carbon dioxide. Though Mars has temperatures generally below freezing, it once had a thicker atmosphere and possibly seas of liquid water, which could have supported life.