Most Of Probe's 14 Ton Mass Is Fuel, Will Burn Up On Re-Entry

Russia's Fobos-Grunt probe (model photographed by Pavel Kolotilov) was launched November 9, headed for one of the moons of Mars. But the mission encountered communications troubles early, and the spacecraft has been stuck in Earth orbit. Now, Russia admits it will fall into the atmosphere in early January, but stresses there is not a serious risk to anyone on the ground.

The Russian space agency, Roscosmos, says between 20 and 30 pieces weighing a total of about 440 pounds or less will survive reentry. That doesn't sound like much left of a spacecraft weighing 14.6 tons, but most of that weight is the fuel it would have used getting to Mars. While highly toxic, the fuel is expected to burn off high in the atmosphere and dissipate without issue.

There is also 22 pounds of radioactive Cobalt-57 in one of the probe's instruments, but Roscosmos tells the Associated Press it will not pose a threat of contamination on Earth.

The Russians have gone a long stretch without launching an interplanetary mission. The last attempt was another unmanned probe to Mars in 1996, but that one was lost after an engine failure.

The Fobos-Grunt mission, which translates to Phobos-Ground in English, was expected to help settle the question of whether the Martian moon Phobos, with its heavily cratered surface, is an asteroid captured by Martian gravity, or a piece of the planet which broke off in a collision with another celestial body.

FMI: http://en.wikipedia.org/wiki/Fobos-Grunt