The first feature humans ever mapped on another planet.
Syrtis Major Planum is a dark, low-relief volcanic shield that stands out sharply against Mars's brighter deserts. In 1659 Christiaan Huygens sketched it and used its motion to measure the Martian day — making it the first surface feature ever identified on another planet.
Claim your plot here →Syrtis Major is a broad, gently sloping shield volcano whose dark tone comes from basaltic and olivine-rich sand kept exposed by strong winds. Because it contrasts so strongly with the surrounding pale dust, Huygens could track it in 1659 as Mars rotated and deduce a day length remarkably close to the true 24.6 hours.
Modern spacecraft revealed the shield's two summit calderas and its wind-swept mineral deposits, which record ancient volcanic activity and interaction with water. Bordering the great Isidis basin, Syrtis Major remains a scientifically rich region and a landmark in the history of planetary astronomy.