Is there really a giant canyon on Mars?

Yes, Mars has the largest canyon in the entire Solar System. It is called Valles Marineris which means Valley of the Mariners (Mariner is another word for sailor or navigator). It is about 2,500 miles (4,000 km) long, 125 miles (200 km) wide, and about 4 miles (7 km) deep. Valles Marineris is about as long as the United States and it covers about 1/5 the distance around Mars. The canyon runs along the Martian equator and is thought to have formed from a giant crack that expanded as Mars cooled after its formation.