In 2020 a Russian space mission will launch at the Martian moon Phobos. The mission, called Phobos-Grunt 2, will collect samples from Phobos and return them to Earth for tests. But it has now been confirmed that such a mission will also return with matter from the red planet itself.
Phobos is a tiny and mysterious object orbiting Mars just 6,000km from the planet’s surface. Some believe it is an asteroid captured by Mars’ orbit; others think it could be a chunk of Mars itself, knocked off early in the planet’s history. Over millions of years impacts by projectiles have blown dust and debris from the surface of Mars onto Phobos. This means that the moon’s regolith, the name given to the surface layer of dust and rock, will contain Martian particles.
The imminence of the planned mission makes the question of how much Martian material is present on Phobos a practical rather than academic one, according to James Head at Brown University. He said: “This work shows that samples from Mars can indeed be found in the soil of Phobos, and how their concentration might change with depth. That will be critical in the design of the drills and other equipment.”
Head carried out the work in collaboration with Ken Ramsley, also at Brown, initially in preparation for the original Phobos-Grunt mission, which launched two years ago. However, an engine failure meant that this first mission was left stranded in Earth’s orbit. The Russian space agency, the Space Research Institute (IKI), is hopeful that the “improved and simplified” Phobos-Grunt 2 will be more successful.
Head and Ramsley’s research concluded, using observed orbital information and modelling techniques, that the regolith of Phobos is around 250 parts per million Martian. Ramsey also predicts that most of the Martian material should be close to the surface of the regolith: “Only recently – in the last several hundred million years or so – has Phobos orbited so close to Mars. In the distant past it orbited much higher up.”
Phobos-Grunt 2 is part of a much bigger Mars project by IKI. In 2018, two cosmonauts will spend a year on the International Space Station (ISS); they will then come back to Earth to perform simulated Martian experiments, before returning to the ISS to simulate their journey back home. A manned exploration of the planet is planned for 2035.