Filed under
geology
15 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. 4.5 billion years agoFormation
The Borealis impact splits Mars in two
The northern lowlands sit 5 km below the southern highlands. The boundary traces an ellipse 10,600 km across — plausibly the largest impact scar in the solar system.
- c. 4.1 billion years agoFormation
The dynamo dies and the air starts leaving
Mars Global Surveyor found the oldest crust magnetised and the great impact basins blank — read as a dynamo dead inside the first half-billion years, though MAVEN data since has reopened the date.
- c. 3.8 billion years agoFormation
Rivers run, and an ocean nobody can prove
Thousands of branching valleys and a delta in Jezero crater show water flowed for a long time. Whether it ever pooled into a northern ocean is still argued.
- c. 3.7 billion years agoFormation
Tharsis rises and tips the planet over
Three hundred million cubic kilometres of magma built a bulge across a quarter of Mars, raised Olympus Mons some 22 km, and probably tipped the spin axis about 20 degrees.
- 31 July and 5 August 1969First Contact
Mariner 6 and 7 find more craters
Two flybys returned 201 pictures and pinned the atmosphere at 6 to 7 millibars, but both happened to cross the oldest, dullest terrain on Mars.
- 14 November 1971First Contact
Mariner 9 arrives into a planet-wide dust storm
The first spacecraft ever to orbit another planet reached Mars to find the surface hidden by dust. It waited, then mapped volcanoes, a 4,000 km canyon and dry riverbeds.
- 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.
- 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.
- 12 September 1997The Rover Decades
Mars Global Surveyor maps the planet Mars Observer lost
Mars Observer died three days short of orbit in 1993. Its instruments were rebuilt as Global Surveyor, which found fossil crustal magnetism and geologically fresh gullies.
- 12 March 2013Follow the Water
Gale Crater held a lake you could have drunk from
Curiosity's first drill hole, 6.4 cm into a mudstone called John Klein, produced clay, sulfur and nitrogen — and an ancient lake of fresh, neutral water.
- 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.