Phobos, the moon of Mars, is slowly falling toward the planet, and scientists still don't know where it came from.
Japan's MMX mission to Phobos aims to bring back samples to test the two theories: a captured asteroid, or debris from a giant impact on Mars.
0:00 A moon crossing the Sun
0:50 Closer than any other moon
1:58 Why Phobos is falling
3:20 The grooves: stretch marks or boulder tracks?
4:26 Where did Phobos come from?
5:33 MMX: going to get a piece
7:18 What the sample could say
8:48 The question
What this film does and does not claim: Phobos is spiralling inward by about 1.8 to 2 metres per century (NASA). Models forecast it will be pulled apart, or crash into Mars, in about 30 to 50 million years; that is a model forecast, not a countdown. The grooves on Phobos are sometimes interpreted as tidal "stretch marks", but rival explanations exist, including boulders rolling out of Stickney crater. As of 12 October 2026, JAXA scheduled MMX's launch for 19 October 2026 (UTC), with a window to 7 November; arrival at Mars, the Idefix rover, sampling and the 2031 return are plans. Drawn diagrams are illustrations, not to scale. No JAXA imagery is used; the mission graphics are original.
Sources
- JAXA, MMX launch announcement (H3 No. 10, Tanegashima) and MMX mission pages
- DLR, "Off to the moons of Mars: MMX mission and Idefix rover ready for launch" (2026)
- NASA Science, Phobos overview; NASA Goddard, "Mars' moon Phobos is slowly falling apart" (2015)
- NASA/JPL, Perseverance Phobos eclipse (PIA25179, 2 Apr 2022)
- Brown University (2018), boulder-track explanation of Phobos' grooves
- Usui et al. (2020), Space Science Reviews: MMX sample analysis and the origin of the Martian moons
Visuals: NASA/JPL-Caltech/ASU/MSSS/SSI (Perseverance Mastcam-Z eclipse video), NASA/JPL-Caltech/University of Arizona (HiRISE PIA10368, PIA10369, enhanced colour), NASA/JPL-Caltech/MSSS (Curiosity PIA26362), NASA, ESA, Z. Levay (STScI) (Hubble PIA21837), NASA/JPL (PIA00078), ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO (Mars Express HRSC), NASA, ESA, CSA, STScI (Webb backdrop). Diagrams and data cards are original.
Narration is a synthetic voice. Independent production, not affiliated with or endorsed by NASA, JAXA, ESA or DLR.
Captured asteroid, or a moon built from impact debris? What do you think the samples will show? Tell us in the comments.
