Mars is the fourth planet from the Sun. Its day is about the same length as Earth's, and it has seasons, an atmosphere, and evidence of ancient rivers.
Why it is hard
The atmosphere is 1% of Earth's, mostly carbon dioxide, and provides no protection from radiation. Getting there takes six to nine months.
Why it is tried
SpaceX is developing Starship with Mars as its stated destination. NASA's Artemis Program precedes it on the Moon.