In 2031, a JAXA capsule is due to land in the Australian desert carrying more than ten grams of dust collected from Phobos. Mixed into that dust may be fragments blasted off ancient Mars—material that could preserve organic chemistry, or perhaps even traces of hypothetical Martian life from billions of years ago.

In 2031, a JAXA capsule is due to land in the Australian desert carrying more than ten grams of dust collected from Phobos. Mixed into that dust may be fragments blasted off ancient Mars—material that could preserve organic chemistry, or perhaps even traces of hypothetical Martian life from billions of years ago.

If the schedule holds, a small Japanese capsule will cross the Australian sky in the 2031 fiscal year and land carrying more than 10 grams of material gathered from Phobos, the larger of Mars’s two moons. Ten grams is about two teaspoons of dry dust. Yet mixed through it may be something much more difficult to collect: fragments of Mars knocked from the planet by ancient impacts and deposited on Phobos over hundreds of millions of years. That po…