The Moons of Mars
On 20 October 2026 (Japan time) JAXA launched MMX, a spacecraft that is to land on Mars's moon Phobos and bring a sample back to Earth in 2031. This film explains what it is going to: the two small moons Asaph Hall found in 1877, how a spacecraft gets to Mars on a Hohmann transfer and why launch windows come about every 26 months, why Phobos orbits inside Mars's synchronous orbit and is slowly spiralling inward while Deimos drifts away, what the Roche limit is and why Phobos is expected to break into a ring tens of millions of years from now, and the two competing ideas for where the moons came from: captured asteroids, or debris from a giant impact. Launch at the right and wrong moment, watch the tides at work, change the Roche limit, break up Phobos, compare the origin stories and land the rover.
Fear and Dread
A spacecraft sets off for the moons of Mars.
Two faint points of light
How Mars’s moons were found.
Lumpy, dark and close
Two moons unlike ours.
Launch windows
Half an ellipse, and a moving target.
Inside the line
Why one moon falls and the other drifts away.
Too close to hold together
Where a planet’s tides win.
A ringed Mars
What may happen tens of millions of years from now.
Captured asteroids?
They look like asteroids. Their orbits do not.
Pieces of Mars?
A collision, a disk, and a dozen moons that fell.
Circling a moon that cannot be circled
A quasi-satellite orbit and a rover.
Ten grams of a moon
Touch down, grab, go home.
A question in a capsule
What the grains could tell us.
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