Right now, a moon is falling toward Mars: about six feet every hundred years, by NASA's count. It is called Phobos. It is 27 kilometers long, it circles the planet three times a day, and nobody can say where it came from.

In this episode, the moon step by step. The size of it and its orbit, 5,989 kilometers above the surface. The fall: the measured rate, the projected end in about 50 million years, and why we do not multiply one number by the other. The crater Stickney, which NASA says takes up about half the moon's surface, and the 85-meter boulder some people call an "object". Then Beyond the Obvious: how ESA's Mars Express weighed Phobos from 45 kilometers away and found less than half the density of Mars, which means a rubble pile with 25 to 35 percent empty space, not a hollow shell. The two origin stories, captured asteroid or debris from a giant impact, with the evidence for and against each. And the Japanese mission MMX, due to launch on October 20, 2026, to land twice on Phobos, collect at least 10 grams, and bring them back to Earth in 2031, after every previous landing attempt at this moon failed.

Every figure comes from NASA, ESA, JAXA and CNES pages, linked in the video description on YouTube. Where the sources disagree or don't know, we say so.

Watch the video edition: https://www.youtube.com/watch?v=9STlqNdY6lU

Narration: synthetic voice. Research, writing and editing: human work. Echoes of the Void.