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science
27 milestones, in chronological order.
- c. 4.56 billion years agoFormation
Mars accretes fast, then stops growing
Hafnium–tungsten dating puts Mars at half its present size within two million years of the solar system's birth. Then it quit growing, at a tenth of Earth's mass.
- c. 4.55 billion years agoFormation
Iron sinks and a dynamo switches on
Molten iron drained to the centre in a few million years, building a core roughly half the planet's radius — how much has been re-argued twice since 2021 — and its churning gave Mars a magnetic field.
- c. 652 – 60 BCEAncient Eyes
Babylon turns Mars into arithmetic
Babylonian scribes logged Mars beside barley prices for six centuries, then used a 79-year repeat to predict where it would be — with no model of why.
- c. 150 CEAncient Eyes
Ptolemy's equant makes Mars predictable
To fit Mars, Ptolemy let it sweep its circle at a steady rate around a point that was not the centre — a cheat that broke Greek doctrine and worked for 1,400 years.
- 499 CEAncient Eyes
Aryabhata fixes Mars's year to within half an hour
The Aryabhatiya assigns Mars 2,296,824 orbits per 4,320,000-year cycle. Work it through with his own day count and the period is 686.9997 days; the modern value is 686.98.
- 877–1375 CEAncient Eyes
Islamic astronomers take the equant apart
Al-Battani re-measured every planetary motion, Ibn al-Haytham argued the equant was physically impossible, and Ibn al-Shatir built the models Copernicus would mirror.
- 1543Ancient Eyes
Copernicus explains Mars's backwards loop
De revolutionibus turned Mars's retrograde loop into a trick of perspective — Earth overtaking it on the inside. The predictions were no better than Ptolemy's.
- 23 May 1576The Telescope Era
Tycho Brahe builds Uraniborg and measures Mars by eye
Tycho fixed Mars to about an arcminute with sighting instruments alone, cross-checking with duplicate observers and correcting for refraction — and the logbooks went to Kepler.
- 1609The Telescope Era
Eight arcminutes of Mars break the perfect circle
A stubborn eight-arcminute gap between Tycho's Mars positions and every possible circular orbit forced Kepler to the ellipse, and rebuilt astronomy around it.
- 1672The Telescope Era
Mars gives up the size of the solar system
Observing the same Mars opposition from Paris and Cayenne gave the first sound distance to the Sun: about 140 million km, seven per cent short of the true value.
- 20 September 1909Canals and Dreamers
Antoniadi dissolves the canals at Meudon
Four nights before opposition, the 83-centimetre Meudon refractor showed Antoniadi a Mars crowded with irregular detail and not one straight line.
- 1947Canals and Dreamers
Kuiper finds carbon dioxide, and no water
A lead-sulphide cell on the 82-inch at McDonald Observatory found the first molecule ever confirmed in the air of Mars: carbon dioxide. Water vapour stayed hidden until 1963.
- July – September 1976First Contact
The Viking biology results that never settled
One of Viking's three biology experiments came back positive at both landing sites. The gas chromatograph found no organic molecules at all, and the argument has never closed.
- 12 August 1983The Rover Decades
Trapped gas proves a meteorite came from Mars
Gas sealed in shock glass inside a 7.9 kg Antarctic stone matched the air Viking had measured in 1976. Terrestrial laboratories suddenly held free samples of Mars.
- 18 February 1993The Rover Decades
Mars's tilt turns out to be chaotic
Two 1993 calculations showed the Martian axis wanders chaotically — one integration ran it from 11 to 49 degrees over 80 million years. The present 25.19 degrees is a low value, not a constant.
- 7 August 1996The Rover Decades
A Martian meteorite is said to hold fossils
Bill Clinton stood in front of the cameras for a 1.9 kg rock from Antarctica. Within five years every line of evidence for Martian microbes had a non-biological answer.
- 28 May 2002The Rover Decades
Odyssey counts neutrons and finds buried ice
Neutron counts fell away over both poles. Odyssey read that as ice within a metre of the surface — by one estimate enough to fill Lake Michigan twice, and a target for landers.
- 10 March 2006The Rover Decades
Mars Reconnaissance Orbiter becomes the eye and the relay
The sharpest camera ever sent to another planet resolves 30 centimetres per pixel from 300 km up, and the same spacecraft relays much of what the rovers below it send home.
- 3 June 2010 – 4 November 2011The Rover Decades
Six men spend 520 days sealed in a Moscow mock-up
Mars-500 ran a Mars mission at full length with nobody leaving the building. Four of the six crew came out with a sleep or behavioural disorder.
- 31 May – 9 December 2013Follow the Water
Curiosity measures the radiation dose of a Mars trip
The rover's dosimeter logged 1.8 millisieverts a day in transit and 0.67 on the floor of Gale Crater — a round trip comes to roughly one sievert, two thirds past NASA's career ceiling.
- 21 September 2014Follow the Water
MAVEN starts weighing the air Mars loses
The first orbiter built for the upper atmosphere measured Mars shedding roughly 100 grams of gas per second to the solar wind — and about ten times that during solar storms.
- 28 September 2015 – November 2017Follow the Water
The streaks that turned back into sand
NASA announced briny water seeping down warm slopes. Two years later the same streaks were shown to stop exactly where dry sand stops, and the claim collapsed.
- 12 January 2018Follow the Water
Ice cliffs expose clean water in the mid-latitudes
Eight eroding scarps at 55 to 58 degrees latitude cut open water ice more than 100 metres thick, its top just 1 to 2 metres down — and visibly banded.
- 26 November 2018Follow the Water
InSight listens to the inside of Mars
The first seismometer set directly on another planet's surface logged 1,300 marsquakes and sized a liquid core. Its heat probe never managed to bury itself.
- 20 April 2021 – 7 August 2023The Present Push
MOXIE makes oxygen out of Martian air
Perseverance carried a toaster-sized box that heated Martian carbon dioxide to 800°C and made 5.4 grams of oxygen — the first time a spacecraft manufactured a consumable on another planet.
- July 2024The Present Push
Leopard spots in a Martian mudstone
Perseverance drilled a rock ringed with vivianite and greigite. On Earth microbes make those minerals; on Mars nobody has yet found a plain chemical route that fits.
- Every 779.9 days — windows in 2026, 2028–29 and 2031The Road AheadPlanned
The 26-month clock that governs everything
Earth and Mars line up for a cheap transfer once every 779.9 days. A six-week hardware delay does not cost six weeks; it costs more than two years.