Mars actually has two moons: Phobos and Deimos. They might more properly be called satellites, however, because they are extremely small, only a few kilometers in diameter. In fact, some scientists think Phobos and Deimos could be asteroids that somehow ended up orbiting Mars instead of crashing into the planet, or they could be leftovers from the time of planetary formation. Another option is that the moons are fragments of Mars, blasted off the planet’s surface by a large asteroid or comet impact.
Whatever their origins, in terms of space missions the moons have been overshadowed by the planet they orbit. If a spacecraft is sent on a 6-month journey of many millions of miles, it seems anti-climatic to have it plop down on a tiny asteroid-like body when Mars itself is so close, beckoning with its many different regions to explore and a complex history to unravel. Russian scientists, however, have been trying to send a spacecraft to Phobos, the larger of the two Mars moons, for many years.
|Artist rendering Phobos-1|
Phobos 1 and Phobos 2 were launched within 5 days of each other in July 1988. Phobos 1 lost communications due to a software glitch that September, but Phobos 2 had better luck and made it all the way to Mars orbit. Before the spacecraft could send its two probes to Phobos, however, the spacecraft’s signal was lost due to a computer malfunction.
The Russian Federal Space Agency proposed sending a new mission to Phobos in 1999. Called Phobos-Grunt (“grunt” being the Russian word for “soil”), this mission aims to gather a sample of soil from the moon’s surface and send it back to Earth for analysis. Although an unmanned sample return mission sounds complicated, the Russian space program has succeeded many times in conducting similar missions closer to home.
The director of the Institute, Erik Galimov, thinks samples from Phobos could help answer many mysteries about the martian moon’s origin and composition. He says that we have been able to learn some details about Phobos by gazing at the moon with telescopes, or by quick flybys of Mars orbiters such as ESA’s Mars Express. These glimpses have shown that Phobos is made of dark material that does not reflect much light. This makes scientists suspect it has a chemical composition similar to that of carbonaceous chondrite asteroids.
But other aspects of the moon can’t be learned simply by staring. For one thing, Galimov says that remote instruments can’t tell us the absolute age of Phobos, while a sample would allow us to measure that precisely. A sample also would allow scientists to measure the chemical isotopes, which could then be compared to the isotopic signatures of martian meteorites that have landed on Earth to see how similar Phobos is to the planet it orbits. Similar studies were conducted on lunar samples, and they indicate that the Earth and our Moon formed from the same kind of source material.
Above: The final architecture of the Phobos-Grunt spacecraft. Credit: NPO Lavochkin
A closer examination of Phobos might reveal if it is one large hunk of rock, or a gravitationally-bound rubble pile as many scientists now suspect. The question of whether Phobos contains water ice, a potential resource for future Mars explorers, also could be answered.
“I think it will be a very positive contribution, because we would have in our hand samples from the Mars area,” says Galimov.
One attraction Phobos holds over Mars is that it costs much less money to go there. Phobos has no atmosphere to contend with, and much lower gravity. Even so, the latest estimated cost for the entire Phobos-Grunt mission is 2.4 billion rubles (about 72 million US dollars). Adding to the complications are the number of instruments that have been added the design plan over the years (the current count is 11 instruments – most NASA spacecraft have 3 or 4 instruments onboard).
One of the planned Phobos-Grunt experiments is the Living Interplanetary Flight Experiment, or LIFE, provided by the U.S.-based Planetary Society. This experiment would carry various microorganisms, as well as a soil colony from the Arctic permafrost, to see how well they endure space travel.
The experiment is controversial because of planetary protection issues – scientists hope to find evidence for life on Mars someday, and are careful to sterilize spacecraft so we don’t inadvertently carry life there. If Phobos-Grunt should accidentally crash on Phobos or Mars, the life contained in the spacecraft probably would not survive for long in the harsh environment, but most scientists don’t want to risk contamination regardless.
One who opposed fiercely was Barry E. DiGregorio, the director of the International Committee Against Mars Sample Return, who criticised the LIFE experiment on the Fobos-Grunt mission as a violation of the Outer Space Treaty of 1967 due to its risk of contaminating Phobos or Mars with the microbial spores and live bacteria it contains. While the mission lands and returns from Phobos, a moon of Mars, the risk to Mars itself is from the possibility of Fobos-Grunt losing control and crash landing on the planet.
The launch of Phobos-Grunt is scheduled to be launched by the end of this year. Whenever the mission does launch, it will take 3 years for the lander to reach the small moon, touch down on the surface, and then return its sample to Earth.
Piggybacked on Phobos-Grunt
Yinghuo-1 will be China's first planetary mission. It will be a very small orbiter that will hitch a ride to Mars with Phobos-Grunt. It will perform studies of Mars from an elliptical, equatorial orbit.
The main scientific objectives include: detailed investigation of the plasma environment and magnetic field; study of Martian ion escape processes and possible mechanisms; ionosphere occultation measurements between Yinghou 1 and Phobos-Grunt, focusing on the sub-solar and midnight regions; and observation of sand storms.
The scientific payload consists of a five-instrument payload including a plasma package (consisting of an electron analyzer and an ion analyzer and mass spectrometer), fluxgate magnetometer, radio-occultation sounder and an optical imager camera with 200 m resolution at best to take pictures of Mars.