China is getting ready to participate in its first interplanetary enterprise, teaming up with Russia, in a daring attempt to retrieve samples from the Martian moon Phobos. The Phobos-Grunt mission--grunt is the Russian word for soil--is scheduled to launch in October 2009, with the samples set to arrive on Earth in 2012 [see photo, "Mock-up"]. If Phobos turns out to have been formed from Mars, the mission will provide a shortcut to obtaining ancient Martian soil. In any case, Phobos-Grunt is Russia's only scheduled planetary mission for the next 10 years, and it is the first sample-return effort since Apollo, more than 30 years ago.
The China National Space Administration and the Russian Federal Space Agency (Roscosmos) signed a formal agreement in March that will allow China to send a small satellite called the CDP-1 to Martian orbit, piggybacking on the Phobos-Grunt orbiter. According to Alexander Zakharov of the Space Research Institute in Moscow, project scientist for the Phobos-Grunt mission, the CDP-1 would test a deep-space tracking system, measure the various constituents of the Martian atmosphere, and study the plasma field around Mars during a one-year period. The Chinese are also contributing a thermal differential analyzer for the gas-chromatograph system, to be used in analyzing the elements contained in soil samples taken from Phobos before they are brought back to Earth. The instrument is being built by the Hong Kong Polytechnic Institute.
The Lavochkin Space Association, in the Moscow area, is the manufacturer of the Phobos-Grunt spacecraft, which is to be launched on a Russian Soyuz-2b rocket and take eight to nine months to reach Mars. Once in orbit, the spacecraft will separate into three individual vehicles: the Chinese Mars satellite, the Russian Phobos orbiter, and the Phobos-Grunt lander [see photo, "Destination"].
DESTINATION: A photograph of the Mars moon Phobos, as seen from NASA's Mars Global Surveyor spacecraft.
Much of the Phobos-Grunt's work will focus on Mars and its atmosphere, but the moon itself has plenty to offer. Phobos and its fellow moon Deimos are named for the sons of Ares, the Greek counterpart of the Roman god Mars (phobos means fear; deimos, terror). Although the moons were discovered in 1877, Jonathan Swift already had a premonition of their existence, astonishingly, in his Gulliver's Travels (1726). Orbiting 5989 kilometers above Mars's surface, Phobos has a period of just 7 hours 39 minutes and is gradually being drawn into the planet--it will crash in about 50 million years.
Because Phobos orbits at roughly twice the rate of Mars's rotation, Phobos-Grunt will undergo a series of complex maneuvers to first enter Martian orbit, where it will stay and perform remote observations of the Martian atmosphere and surface. Then the orbiter will launch the lander to the surface of Phobos a month or two later. The lander will spend several months collecting samples with the aid of a robotic arm that can dig down to a depth of 1 meter.
Using a cache of scientific instruments, it will study the physical, chemical, and structural properties of Phobos's surface and inner structure and send the data back to Earth. After that has been accomplished, a sample-return canister mounted on top of a small rocket (called an Earth-return vehicle) located on the Phobos lander will be filled with 1 kilogram of soil, dust, and rock. ”Because Phobos has no atmosphere or large gravity field to contend with, launching a small rocket should be relatively simple,” Zakharov says.
If all works according to plan, the return vehicle will blast off from Phobos and head toward Earth, taking from seven to 18 months to arrive. The sample container could either be picked up in Earth orbit by a Russian spacecraft or enter Earth's atmosphere to land at some location in Siberia and be retrieved by helicopter.
The origins of the Martian moons are a mystery that Phobos-Grunt intends to illuminate. There are two contending theories: that Phobos was formed from Mars and hurled into orbit by a collision with a large asteroid or comet millions of years ago; or that Phobos is a captured asteroid from the asteroid belt, which is located between Mars and Jupiter.
If Phobos was once part of Mars, it may contain ancient subsurface water ice or even ancient microfossils from a time when Mars was warmer and wetter.
Thomas C. Duxbury, NASA's Stardust project manager and a coinvestigator on the Soviet Phobos-2 mission in 1988 that ended prematurely because of a computer glitch, says he believes Phobos and Deimos were blasted off the surface of Mars by an impact event. If that turns out to be the case, ”then we have a much simpler Mars sample-return mission,” he points out.
Alternatively, if Phobos was an asteroid, then its soil can provide planetary scientists with a sample of the raw material from which the planets were formed. In January 2006, NASA's Stardust space vehicle was the first to successfully bring back samples of a comet to Earth. They are believed to contain material that existed before the solar system came about. Material in the asteroid belt, on the other hand, is thought to be the debris left over from the formation of the planets.
Given that NASA has now put its own Mars Sample Return project on hold until 2020 or later, could Phobos-Grunt also be a dress rehearsal for an eventual Mars sample-return mission? Mikhail Marov of the Keldysh Institute of Applied Mathematics in Moscow, principal investigator on the Phobos-Grunt mission, explains: ”The experience gained from Phobos-Grunt will be extremely valuable for the follow-up Mars missions that are now in the Russian Science Academy's [planetary exploration] blueprint.”