Mars shares Earth's polar ice caps, four seasons, and a 24.6-hour day. But beneath these familiar rhythms lies a freezing world where the air is lethal and gravity is weak.
If you stood on the Martian surface, the mechanics of these similarities would feel remarkably familiar. While a standard solar day on Earth is exactly 24 hours, a Martian day (called a sol) is only slightly longer at 24.6597 hours. The shared seasonal cycles exist because the Martian axis is tilted at 25.19 degrees, incredibly close to Earth's 23.44-degree tilt. Both terrestrial planets also feature dynamic geography with deep canyons, towering mountains, and ancient, dried riverbeds.
The similarities end when comparing the physical scale of the two planets. Mars is surprisingly small. It has an equatorial diameter of about 6,779 km, which is just 53% of Earth's size, and it holds roughly 11% of Earth's mass. Because of this smaller mass, the Martian surface exerts a gravitational pull of only 3.73 m/s²—roughly 38% of what is felt on Earth.
The most extreme divergence between the two worlds is their habitability. Earth maintains a dense, nitrogen- and oxygen-rich atmosphere with an average surface pressure of 1,014 millibars. This thick blanket traps heat and supports liquid water, keeping the global average temperature at a comfortable 15°C (59°F). In contrast, the Martian atmosphere is 95% carbon dioxide and has a surface pressure of just 6.36 millibars—more than 100 times thinner than Earth’s. This thin air cannot hold much heat, resulting in a freezing global average of −59°C (−74°F).