Mars’ moon seen close-up

Mars Express image of Phobos

The larger of Mars' two moons, Phobos, as seen in a newly returned image from Europe's Mars Express spacecraft. The image has been enhanced to illuminate darker areas. The resolution is 4.1 metres per pixel.

MARS EXPRESS HAS RETURNED images from its close fly-by of one of Mars’ moons, Phobos, on January 9, 2011. The European Space Agency (ESA) spacecraft zipped past the moon at a distance of only 100 kilometres.

Phobos is the larger and closer of the two moons of Mars, the other being Deimos. Both moons were discovered in 1877. With a mean radius of 11.1 km, Phobos is 7.24 times as massive as Deimos. It is named after the Greek god Phobos (which means “fear”), a son of Ares (Mars).

A small, irregularly shaped body, Phobos orbits about 9,377 km from the centre of Mars, closer to its planet than any other known planetary moon. It orbits so close to the planet that it moves around Mars faster than Mars itself rotates. As a result, from the surface of Mars it appears to rise in the west, move rapidly across the sky (in 4 h 15 min or less) and set in the east.

Phobos’ orbital radius is decreasing, and it will eventually either impact the surface of Mars or break up into a planetary ring.

Phobos is one of the least-reflective bodies in the Solar System, and features a large impact crater, Stickney crater.

Here’s a video of Phobos compiled from images taken by Mars Express and NASA’s Viking spacecraft.

Keeping an eye on Mars

Mars Express is Europe’s first planetary mission. At launch, the mission consisted of an orbiter carrying seven instruments for remote sensing observations of the planet, and a lander (Beagle 2) for on-the-spot measurements of Martian rock and soil.

While approaching Mars on 19 December 2003, Beagle 2 was released and started its 6-day journey to the planet’s surface. However, the attempts to communicate with it on 25 December 2003, the date of its expected touchdown, were not successful. The Beagle 2 mission was declared lost on 6 February 2004. In contrast, the Mars Express orbiter started science observations as planned in January 2004, and since then it has been delivering an incredible amount of scientific results.

The ‘Express’ part of the name highlights the fact that the spacecraft was built more quickly than any other comparable planetary mission. In fact, it took only five years from mission approval to launch.

In addition to global studies of the surface, subsurface and atmosphere of Mars with unprecedented spatial and spectral resolution, the unifying theme of the Mars Express mission from orbit is the search for water in its various states, everywhere on the planet by all its seven instruments using different techniques.

Artist's concept of the Fobos-Grunt mission

Artist's concept of the Russian Fobos-Grunt mission, due for launch later this year.

The mission was originally planned for one Martian year (687 days). It has already been extended three times, and is now funded for operations until the end of 2012.

Russia to try again with Mars mission

Fobos-Grunt (meaning “Phobos Ground”) is a planned unmanned Russian “sample return” mission to Phobos. (The Chinese Mars orbiter Yinghuo-1 will be piggyback with the mission.) Scheduled for launch late 2011 or early 2012, Fobos-Grunt will be the first Russian interplanetary mission since the failed Mars 96 mission.

If successful, this will be the first large extraterrestrial sample from a planetary body brought back to Earth since the last sample return mission by Luna 24 in 1976. (The Japanese Hayabusa probe has returned with a sample from 25143 Itokawa in June 2010, but the sample only consisted of some particles of dust.)

Fobos-Grunt will also study Mars from orbit, including its atmosphere and dust storms, plasma and radiation. It is currently scheduled to be launched in November 201.

The journey to Mars is scheduled to take about ten months. The spacecraft will then spend several months studying the planet and its moons from orbit, before landing on Phobos. The current timeline is for arrival in October 2012 and landing in February 2013.

Immediately after the touchdown, the lander will load a soil sample into a return rocket. In case of a breakdown of communications with mission control, it can enter an emergency mode to collect samples and still send them home in the return rocket. Normal collection could last from two days to a week.

Mars Express image of Phobos

Image of Phobos with a resolution of 8.2 metres per pixel. The ellipses mark the spots previously planned (red) and currently considered (blue) as landing sites for the Russian Fobos-Grunt mission.

The robotic arm can collect rocks up to about half an inch in diameter. It ends in a pipe-shaped tool that splits to form a claw. This encloses a piston that will push the soil sample into an artillery-shell-shaped container. A light-sensitive photo-diode in the claw will help scientists confirm that the device did scoop material. They hope also to see images of trenches the claw leaves on the surface. The manipulator should perform 15 to 20 scoops yielding a total of 85 to 160 g of soil.

The return rocket will sit atop the spacecraft, and will need to rise at 35 km/h to escape Phobos’ gravity on the return journey. To protect experiments remaining on the lander, springs will vault the rocket to a safe height, at which its engines will fire and begin manoeuvres for the eventual trip to Earth.

The lander’s experiments will continue in-situ on Phobos’ surface for a year.

Adapted from information issued by ESA / DLR / FU Berlin (G. Neukum) /

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