Mars

The most visited planet beyond Earth. As of 2024: 50 missions attempted, ~26 successful. Currently active: Curiosity rover (2012–), Perseverance rover (2021–), Ingenuity helicopter (2021–2024), MAVEN orbiter, MRO, Odyssey, Mars Express, Tianwen-1, Hope orbiter.

Notable geography

Olympus Mons — largest volcano in the solar system. 21.9 km high (2.5× Everest), 600 km across. So wide that if you stood at the summit, the edges would be beyond the horizon. Likely still volcanically active within the last few million years.

Valles Marineris — a canyon system 4,000 km long, 200 km wide, 7 km deep. If placed on Earth it would span the continental United States. Formed not by water erosion but by tectonic rifting.

Recurring slope lineae — dark streaks that appear seasonally on steep slopes. Initially thought to be briny water seeps. Current consensus leans toward dry granular flows. The question of present liquid water on Mars remains open.

Atmosphere

96% CO₂, 1.9% Argon, 1.9% N₂, trace O₂. Surface pressure: ~0.6% of Earth’s — equivalent to 35 km altitude on Earth. Too thin to support liquid water at the surface, but thick enough for dust storms that occasionally engulf the entire planet for months.

MOXIE (on Perseverance) demonstrated in-situ oxygen production from CO₂ in 2021 — a first step toward the oxygen generation a crewed mission would require.