Mars

Mars at a glance

Property	Mars	Earth	Ratio
Diameter	6,779 km	12,742 km	0.53
Mass	6.4 × 10²³ kg	5.97 × 10²⁴ kg	0.107
Surface gravity	3.71 m/s²	9.81 m/s²	0.38
Atmospheric pressure	~600 Pa	101,325 Pa	0.006 (0.6%)
Mean surface T	-65°C	15°C	—
Day length	24h 37min	24h	1.027
Year length	687 days	365.25 days	1.881
Distance from Sun	1.52 AU	1.0 AU	1.52
Number of moons	2 (Phobos, Deimos)	1 (Moon)	—

The thin atmosphere

Component	Mars	Earth
CO₂	95%	0.04%
N₂	2.6%	78%
Argon	1.9%	0.93%
O₂	0.16%	21%
Water vapor	0.03%	0-4%

Pressure varies seasonally as polar CO₂ freezes/sublimates — cycle moves ~25% of atmosphere between solid and gaseous phases.

Major surface features

Feature	Description
Olympus Mons	22 km tall shield volcano; largest in solar system
Tharsis Bulge	Volcanic plateau; cluster of huge volcanoes
Valles Marineris	4000 km canyon; 7 km deep
Hellas Basin	2300 km diameter impact crater; 7 km deep
Polar ice caps	Water ice + frozen CO₂; seasonal variations
Northern lowlands	Smoother terrain; possibly ancient ocean basin
Southern highlands	Heavily cratered; older terrain

Exploration timeline

Mission	Year	Achievement
Mariner 4	1965	First flyby; 21 photos
Viking 1, 2	1976	First landers; soil tests
Pathfinder/Sojourner	1997	First successful rover
Spirit, Opportunity	2004	Long-duration rovers
Curiosity	2012	Nuclear-powered, still operating
InSight	2018	Marsquake measurements
Perseverance + Ingenuity	2021	Sample collection, helicopter flight
Tianwen-1 (China)	2021	Orbiter + lander + rover

JavaScript — Mars calculations

// Mars constants
const M_MARS = 6.4171e23;
const R_MARS = 3389.5e3;
const G = 6.674e-11;

// Surface gravity
const g_mars = G * M_MARS / (R_MARS * R_MARS);
console.log(`Mars g: ${g_mars.toFixed(3)} m/s²`);  // 3.71

// Weight on Mars vs Earth
function weightOnMars(earth_weight_N) {
  return earth_weight_N * 0.378;
}

console.log(`Person 700N on Earth weighs ${weightOnMars(700).toFixed(0)}N on Mars`);

// Escape velocity
const v_escape = Math.sqrt(2 * G * M_MARS / R_MARS);
console.log(`Mars escape: ${(v_escape/1000).toFixed(2)} km/s`);  // 5.03

// Solar flux at Mars vs Earth
const solar_flux_earth = 1361;  // W/m²
const solar_flux_mars = solar_flux_earth / (1.524 * 1.524);
console.log(`Solar flux at Mars: ${solar_flux_mars.toFixed(0)} W/m²`);  // ~586

// Year length from Kepler's 3rd
const T_earth = 365.25;
const T_mars = T_earth * Math.pow(1.524, 1.5);
console.log(`Mars year: ${T_mars.toFixed(0)} days`);  // 687

// Distance traveled by orbiting Mars
const orbit_radius = 1.524 * 1.496e11;
const mars_orbit_speed = Math.sqrt(G * 1.989e30 / orbit_radius);
console.log(`Mars orbital speed: ${(mars_orbit_speed/1000).toFixed(2)} km/s`);  // 24.1

Why Mars matters

• Astrobiology. Best candidate for past or current extraterrestrial life in solar system.
• Human exploration. Target for first crewed interplanetary mission (NASA Artemis-Mars, SpaceX).
• Comparative planetology. Why did Mars lose its atmosphere while Earth kept hers?
• Solar system formation. Mars provides a well-preserved record of early solar system.
• Resource utilization. Water ice, CO₂, regolith — basis for in-situ resource utilization (ISRU).
• Atmospheric science. Dust storms, CO₂ cycle inform Earth's climate science.
• Geology. Olympus Mons, Valles Marineris — unique geological structures on Mars.

Common misconceptions

• Mars looks "Earth-like in pictures." Misleading — atmosphere too thin, T too cold, radiation too high. Looks like cold desert in images, but is much more inhospitable.
• Dust storms are dangerous to rovers. Reduce solar power and visibility but rarely catastrophic. Wind force is low (thin atmosphere). Movie "The Martian" exaggerated this.
• Mars has water you can drink. Water exists as ice or trace vapor; no liquid surface water (boils at low pressure). Future colonists would extract from ice.
• Mars's red color is bright. Actually muted — like a desert plus dust haze. From space, Mars appears reddish-orange, not the saturated red sometimes shown.
• Phobos and Deimos are like Earth's Moon. They're tiny irregularly-shaped captured asteroids; not at all like our spherical Moon.
• Distance is constant. Mars's distance from Earth varies from ~55 million km (close approach) to ~400 million km (far side of Sun). Mission timing matters greatly.