DEEP FIELDan atlas of the observable universe

M·01 · The red planet

Mars — the world next door

Half Earth's size, a third of its gravity, and close enough that we have thrown more machines at it than at any world besides our own. Mars is the only planet we know of inhabited entirely by robots — and the only one where the footprints, when they come, will be the first. The globe below is live: hover the markers to read the terrain.

— hover a marker —
Diameter6,779 km (0.53 × Earth)
Gravity0.38 g
Day (sol)24 h 37 m
Year687 Earth days
Distance from Earth54.6 – 401 million km
Moons2 — Phobos & Deimos

M·02 · The terrain

A world of records

Mars does not do things by halves. It holds the largest volcano in the solar system, a canyon that would stretch from New York to Los Angeles, and a planet-wide split personality that scientists still argue about.

Olympus Mons

A shield volcano 21.9 km high — roughly two and a half Everests stacked — and about 600 km across at the base. If you stood at its summit you could not see its edges: they curve over the horizon. Its slopes average only about 5°; you could walk up it, if you had a few weeks and a spacesuit. It grew so large because Mars has no plate tectonics — the crust never slid off the hotspot, so the volcano just kept stacking lava in one place for a billion years or more.

Valles Marineris

A canyon system roughly 4,000 km long, up to 200 km wide, and as much as 7 km deep — the Grand Canyon would fit inside one of its side channels. It is probably not a river canyon at all but a tectonic crack: a place where the crust pulled apart as the neighboring Tharsis volcanic bulge loaded the planet's shell, later widened by landslides, ice, and outflow floods.

The two-faced planet

Mars's deepest mystery is visible from orbit: the southern hemisphere is old, high, and battered with craters; the northern third of the planet is young, low, and smooth — as if something planed it flat. The leading explanations are a giant impact early in Mars's history or ancient internal overturn. Either way, the northern lowlands are exactly where an early ocean would have pooled.

Lava flows on the flanks of Olympus Mons imaged from orbit

Olympus Mons lava flows — NASA/JPL

M·03 · The water story

The planet that dried out

Four billion years ago Mars had rivers, lakes, and possibly a northern ocean. The evidence is carved into the surface: dried deltas, meandering channel beds, shorelines, and minerals that only form in standing water. Drag the slider to run the clock.

4.1 billion years ago — Noachian

What the water left behind

Jezero crater — where Perseverance now drives — was a lake. Its western rim carries a textbook river delta, the kind that only builds when flowing water hits standing water and drops its sediment for centuries. Curiosity, in Gale crater, drilled mudstones laid down in a lake that persisted for millions of years. Orbiters have mapped clays and sulfates across the ancient south: minerals that are, in effect, fossilized chemistry of wet environments.

Where the water went

Some of it escaped to space — more on that in the next section. But a great deal is still there: locked in the polar caps, bound inside minerals, and frozen as buried ice sheets. Radar surveys and the SWIM ice-mapping effort have found accessible subsurface ice down to mid-latitudes — close enough to the equator to matter for future crews, who will want to mine drinking water and rocket propellant rather than haul it from Earth.

The river delta in Jezero crater imaged by Perseverance

The Jezero delta — the reason Perseverance landed where it did. NASA/JPL-Caltech

M·04 · The thin air

An atmosphere lost

Martian air is 95% carbon dioxide at less than 1% of Earth's surface pressure — thin enough that liquid water boils at body temperature, thick enough to carry planet-swallowing dust.

The stripping

Mars's core cooled early and its global magnetic field died with it, roughly four billion years ago. Without that shield, the solar wind has been sandblasting the upper atmosphere ever since. NASA's MAVEN orbiter watched it happen in real time: ions torn off the top of the sky at rates that surge during solar storms. Run that loss backward over eons and you get the answer to where much of the early, thicker atmosphere went — carried off into space, an ounce at a time.

The dust

What air remains can still organize itself into weather of planetary scale. Local dust storms merge into regional ones; every few Mars years, one goes global. The 2018 event wrapped the entire planet in a sky so dark that the solar-powered Opportunity rover — fourteen years into a ninety-day mission — fell silent beneath it and never woke. Dust, not distance, is the quiet enemy of everything we send there.

Dust devil tracks crossing the Martian surface

Dust devils on the march — NASA/JPL/HiRISE

Composition95% CO₂ · 2.8% N₂ · 2% Ar
Surface pressure~610 Pa (~0.6% of Earth)
Mean temperature−63 °C
Global magnetic fieldnone — lost ~4 Gya

M·05 · Two small companions

Phobos & Deimos — moons on a deadline

Mars keeps two lumpy, dark moons, each small enough to fit inside a city's ring road. Whether they are captured asteroids or debris from an ancient impact is still an open question — their orbits argue for impact, their looks argue for capture.

Phobos

● 27 × 22 × 18 km

Orbits just 6,000 km above the surface — closer to its planet than any other moon in the solar system — and circles Mars in 7 hours 39 minutes, faster than Mars rotates. From the ground it rises in the west and sets in the east, twice a day. Tidal forces are dragging it inward by about 1.8 meters per century; within roughly 50 million years it will either smash into Mars or shred into a ring. The grooves already scoring its surface may be the first stretch marks of that end.

Deimos

● 15 × 12 × 11 km

The outer moon, small and smooth, orbiting every 30 hours. From the Martian surface it looks like a bright, slow star. Unlike its sibling it is drifting gently outward, and will one day leave Mars entirely. Japan's MMX mission intends to visit both moons and return a sample from Phobos — which may finally settle where the pair came from, and might even carry bits of Mars itself, blasted onto Phobos by ancient impacts.

Phobos, the larger and closer of Mars's two moons

Phobos — NASA/JPL

M·06 · The ground crew

The rovers — a lineage

Six wheeled machines have driven on Mars. Each one was built on the lessons of the last, and each landing site was chosen to ask a sharper question than the one before. Click a marker on the map to read each mission's story — landers included.

Select a landing site

Every marker on the map is a machine humanity landed on another planet. Tap one.

The pathfinder era

Sojourner (1997) was the proof — a microwave-oven-sized rover that drove 100 meters and showed wheels work on Mars. Spirit and Opportunity (2004) were the geologists: twin rovers sent to opposite hemispheres to hunt for water's fingerprints. Spirit lasted six years against a ninety-day plan. Opportunity drove a marathon — 45.16 km over fourteen years — and found ancient acidic lakebeds before the 2018 dust storm ended it.

The laboratory era

Curiosity (2012) changed the scale: a car-sized nuclear-powered lab lowered on a rocket sky crane. In Gale crater it drilled lakebed mudstones, found organic molecules and methane that puffs with the seasons, and is still climbing Mount Sharp today, reading the layers like pages. China's Zhurong (2021) made it a two-nation club, driving Utopia Planitia before winter dust ended its run.

The astrobiology era

Perseverance (2021) is the first rover openly hunting for signs of ancient life, caching samples in Jezero's delta for eventual return. It brought a passenger: Ingenuity, a 1.8 kg helicopter meant to fly five times as a technology demo. It flew seventy-two, over nearly three years, becoming the first aircraft on another world and scouting terrain no rover could reach — until a rotor clipped the dunes in January 2024.

Perseverance selfie with Ingenuity helicopter
Perseverance & Ingenuity, Jezero crater
Sojourner rover viewing the Pathfinder lander, 1997
Sojourner looks back at Pathfinder, 1997
Spirit rover stretching its arm
Spirit, sol 85, Gusev crater

M·07 · The fleet overhead

Orbiters — the standing watch

While rovers crawl, a small fleet circles overhead — photographing, sniffing the upper air, and relaying nearly every byte the surface machines send home. Mars has better mapping coverage than parts of Earth's ocean floor.

OrbiterAgencyOn stationClaim to fame
2001 Mars OdysseyNASA2001 –Longest-serving spacecraft at any planet beyond Earth; found buried hydrogen — the first sniff of subsurface ice
Mars ExpressESA2003 –Radar that sounded the polar caps; two decades of stereo color mapping
Mars Reconnaissance OrbiterNASA2006 –HiRISE camera resolves things the size of a desk; photographed rovers from orbit
MAVENNASA2014 –Measured the solar wind stripping the atmosphere — solved where the air went
ExoMars TGOESA/Roscosmos2016 –Hunts trace gases; put the methane mystery under a microscope — the case file →
Hope (Al-Amal)UAE2021 –First Arab interplanetary mission; watches Martian weather planet-wide
Tianwen-1CNSA2021 –China's first Mars orbiter; carried and relayed for the Zhurong rover
Artist concept of Mars Reconnaissance Orbiter over Mars

Mars Reconnaissance Orbiter — twenty years of staring. NASA/JPL

M·08 · The return ticket

Sample return — the hardest trick

No mission has ever launched from the surface of Mars. That is the entire problem — and the entire point.

Perseverance has been filling ultra-clean titanium tubes with rock cores from the Jezero delta — dozens cached so far, including a backup depot laid out on the surface like a supply drop for a future mission. These are the most carefully chosen rocks in history: lakebed sediments and delta muds, the exact material where fossilized microbial chemistry would hide if Mars ever had it.

Getting them home requires a relay no one has performed: land a rocket on Mars, load it, launch it to orbit, catch the container with a second spacecraft, and fly it back to Earth. The program has been restructured as costs grew — NASA has been weighing leaner architectures, including commercial landers — but the samples themselves are already safe in their tubes, waiting. Rocks are patient.

Six sealed Perseverance sample tubes

Sealed cores, waiting for a ride home. NASA/JPL-Caltech

Why it mattersEarth labs can run tests no rover can carry
The prizeA possible answer to "was Mars ever alive?"

M·09 · The crewed question

Getting people there

Mars and Earth line up for an efficient trip only once every 26 months. Miss the window, wait two years. The orrery below runs the actual geometry — watch the transfer arc light when the planets phase into alignment.

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The trip

A minimum-energy transfer takes roughly seven to nine months each way, plus a stay on Mars of about a year and a half waiting for the return window — a round trip near three years. Faster trajectories exist; they cost propellant, and propellant costs launches.

The hazards

Outside Earth's magnetic field, crews take cosmic radiation the whole way. Add bone and muscle loss in microgravity, dust fine enough to invade machinery and lungs, and a 4-to-24-minute one-way light delay that makes Earth's help advisory at best. Mars does not forgive improvisation.

Living off the land

The unlock is ISRU — in-situ resource use. Perseverance's MOXIE instrument already proved the first step, electrolyzing Martian CO₂ into oxygen across sixteen runs. Scale that up, add mined water ice, and a crew can make air and rocket propellant on site. NASA's Artemis-to-Mars roadmap and SpaceX's Starship architecture disagree on the vehicle, but agree on that much: you refuel on Mars, or you don't go.

M·10 · Mars on Earth

The rocks that came to us

We already own pieces of Mars. Big impacts blast rock off its surface fast enough to escape, and a few of those wanderers eventually fall to Earth — around 400 confirmed Martian meteorites so far, identified by trapped gases that match the Martian air Viking measured.

The most famous is ALH84001, plucked off the Allan Hills ice in Antarctica in 1984. In 1996 a NASA team announced it might contain fossilized Martian microbes — worm-like shapes, carbonate globules, magnetite crystals. The President announced it on the White House lawn. The claim did not survive scrutiny: each feature was shown to form without biology. But the episode built modern astrobiology, taught the field the standard of evidence "extraordinary claims" demand, and put sample return at the top of the agenda — where it has stayed ever since.

Electron microscope view of structures inside meteorite ALH84001

ALH84001 under the electron microscope — the shapes that fooled the world for a summer. NASA

M·11 · The idea of Mars

The planet in the imagination

No other world has done more work in the human mind. Mars has been a god of war, a dying civilization, an invasion fleet, and a second home — usually all at once.

It started with a translation error. In 1877 the Italian astronomer Giovanni Schiaparelli mapped fine lines on Mars and called them canali — channels. English readers heard canals, and canals need diggers. The American astronomer Percival Lowell built an observatory in Arizona largely to chart them, and wrote bestselling books describing a dying race pumping polar water across a desert planet. The canals were an optical illusion — the eye stitching random detail into lines at the edge of vision — but by the time telescopes proved it, the idea had escaped into culture. H. G. Wells inverted Lowell's sympathetic Martians into the invaders of The War of the Worlds (1898); Orson Welles's 1938 radio version panicked listeners who tuned in late. A century of fiction — Bradbury's elegies, Robinson's terraforming trilogy, The Martian's duct-tape optimism — has kept Mars as the default stage for the question underneath all of it: what happens when we arrive?