"This is very intriguing as it implies the interaction of silicate materials with liquid water on the parent body prior to incorporation into Phobos," Marco Giuranna, with Istituto Nazionale di Astrofisica in Rome, said in a statement.
The mineral could have formed on Phobos, but that would mean the moon had enough heat to keep liquid water stable, he added.
The scientists also found other minerals on Phobos that appear to match the types of minerals found on Mars. And, they determined that Phobos, which orbits about 3,700 miles from the planet's surface, is rather spongy, unlike denser material from meteorites that are associated with asteroids. A porous asteroid probably wouldn't have survived getting captured by Mars, the astronomers point out.
The research was presented this week at the European Planetary Science Congress in Rome.
Phobos is the target of a joint Russian-European sample return mission scheduled for launch next year.
(Image: Phobos, a chip off the home world? Credit: NASA/JPL/University of Arizona.)