Physical Profile

Mars is the fourth planet from the Sun and the outermost terrestrial world. It orbits at more than 200 million km from the Sun, coming within about 60 million km of Earth at its closest approach. The planet is roughly half Earth’s diameter, giving it about 15 % of Earth’s volume. Surface temperatures average around –60 °C, and the iconic red hue comes from iron‑rich dust that oxidizes into rust and coats basaltic rock.

Surface Geography and Geology

The planet displays a stark hemispheric dichotomy: the northern plains are smooth and lie several kilometers lower than the heavily cratered southern highlands. A massive uplift called the Tharsis bulge dominates the western equatorial region and supports the solar system’s largest volcano, Olympus Mons. Adjacent to Tharsis, the Valles Marineris canyon stretches 4,000 km long, 200 km wide, and 7 km deep, likely forming as a radial crack when the bulge rose.

Atmosphere and Weather

Mars possesses a thin atmosphere with surface pressure less than 1 % of Earth’s, composed mainly of carbon dioxide. Seasonal cycles cause up to one‑third of the atmospheric mass to freeze onto the polar caps during winter. Weather includes seasonal winds, dust devils, and spring avalanches triggered by thawing carbon dioxide. The thin air offers little shielding, leaving the surface heavily cratered.

Moons

Mars has two small moons, Phobos (≈ 25 km across) and Deimos (≈ 15 km across), thought to be captured asteroids from the nearby belt. Phobos orbits faster than Mars rotates, spiraling inward due to tidal forces and is expected to collide with the planet in a few million years. Deimos follows a more distant, stable orbit.

Water and Habitability

Today, water exists as ice at the poles and in mid‑latitude deposits, with no confirmed liquid on the surface. Geological evidence—ancient river channels, lakebeds, sedimentary layers, and possible oceans—indicates a warmer, wetter past. Atmospheric loss likely resulted from the shutdown of Mars’s internal dynamo, eliminating its magnetic field and allowing solar wind to strip the atmosphere. Curiosity has detected simple organic molecules and episodic methane spikes, suggesting that life could have arisen early in Mars’s history.

Future Exploration

Robotic missions have mapped the planet and sampled its chemistry, but human presence faces challenges such as radiation, vacuum, and life‑support logistics. One proposed strategy for a permanent base involves using lava tubes accessed through surface “skylights” to shield occupants from radiation and dust storms. Continued exploration aims to assess habitability, resource utilization, and the feasibility of long‑term colonization.