Greetings again to all Phobos and Mars aficionados!

Christian Andreas Doppler (29 November 1803 – 17 March 1853)

The closest-ever flyby of Phobos to date will be dedicated to an experimental method called 'radio sounding'. The way radio sounding works is that we place the object (think a celestial body) we want to investigate close to the trajectory of a moving vehicle (think a spacecraft) equipped with a very stable and precise radio transmitter. We also need a very sensitive receiver equipped with measurement devices to record the received signal (think ground stations). The transmitter  on the moving vehicle sends out a continuous unmodulated signal (meaning no actual data will be transmitted - just an 'empty' carrier signal). The receiver receives the signal and then sends that signal to the measurement equipment, which will record the famous Doppler shift of the received signal's frequency (access more details under the 'Full story' link below) -- Hannes.

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NASA's Deep Space Network (DSN) will play a critical role in the central science activity for the 3 March flyby.

The American space agency's giant 70m station at Robledo, Spain (DSS-63), will be enlisted to track ESA's Mars Express during Phobos flyby to record extremely precise Doppler data - which in turn will enable Mars Express scientists to obtain the best-ever measurements of Phobos gravity and hence mass (click on 'Full story' for more details). -- Daniel

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From Earth all natural celestial objects rise in the east and set in the west.  The same is not true at Mars.  Phobos goes in reverse.  

If you were to stand on the surface of the Red Planet, Phobos would rise in the west.  It would appear about one-third the apparent size of our Moon as seen from Earth’s surface, and it would cross the Martian sky against the flow of the other celestial objects before setting in the east.  What makes Phobos so different?

Simple: it orbits unusually close to Mars, at an average altitude of around 9400 km (compared with our Moon’s distance from Earth of around 385 000 km).  To maintain such a low orbit, Phobos has to move so quickly that it out-paces the planet’s rotation.  Mars rotates once ever 24 hours 37 minutes, whereas Phobos completes an orbit in just 7 hours 39 minutes.

Hence, Phobos is constantly overtaking the surface of the planet.  All other natural celestial objects, including Mars’s second moon Deimos, are moving more slowly in relation to the surface of the planet and so are brought into view as the surface turns to face them. This causes them to rise in the east and set in the west.

From Earth, only artificial space-borne objects, such as the International Space Station, are in such low orbits and travelling so fast that they appear to rise in the west.

Back on Mars, the Phobos weirdness does not stop with its backward journey through the sky.  Because the moon is in such a low orbit above the equator, it can never be seen from inside the Martian polar circles. -- Stuart

Good morning from the Mars Express Dedicated Control Room (DCR) at ESA/ESOC!

Yesterday's orbit change manoeuvre went as planned, and this morning at 05:52 UTC (06:52 CET) we passed by Phobos at a predicted altitude of 991 km, the first in our series of 12 planned flybys. This pass was used to acquire PFS spectrometer readings and to scan the moon with our MARSIS subsurface sounding radar.

As I write these lines, data from this exciting event is being downloaded from Mars Express via NASA's DSN trackign station at Goldstone, in California's Mojave dessert, and we are all anxiously awaiting the analysis by the flight dynamics experts at ESOC to show the actual, observed fly-by parameters.

Stand by for more exciting news about our visits to a moon that has so far provided us with many more questions than answers. -- Hannes

PS: Read today's full report in the ESA website:
http://www.esa.int/esaCP/SEM4Q1NEG5G_index_0.html
http://www.esa.int/SPECIALS/Mars_Express/SEM4Q1NEG5G_0.html 

Greetings from the flight deck of Mars Express!

As you may have read, we are up to something really exciting: A visit to Mars' moon Phobos! In fact, it will be the closest ever attempted. This visit will then be followed by several more encounters during the year, all at different distances and Sun illumination angles, to get the best shots from every possible vantage point. We aim to 'weigh' the moon, photograph it and scan it with spectrometers to unlock the secrets it has so far withheld from our grasp.

This blog is dedicated to these exciting events. Join us as we embark on a trip to one of the most mysterious bodies of the solar system by checking our regular blog entries as more information becomes available!

Today we generated and prepared the telecommands that will initiate the first of a series of manoeuvres that will lead to this encounter. This crucial manoeuvre will take place in the wee hours of Monday, 15 February. The command sequences, which will be uploaded to Mars Express in the coming hours, will drive the first engine burn and lock down moving parts on board the spacecraft in preparation for engine ignition.

So buckle up and hold on to your hats. Phobos, the moon of "Fear", is coming near!-- Hannes

No that’s not a typo; it's a message Galileo sent to the brilliant German astronomer Johannes Kepler. And it led to the enduring belief that Mars possessed two moons, centuries before they were actually discovered.

Galileo was an observer, using his newly built telescope to sweep the skies and look at things no human had seen before. He saw the mountains on the Moon, the phases of Venus and the stars of the Milky Way. Kepler was a theoretician, gifted in mathematics. He had already performed a feat nobody had ever done by describing planetary motion in mathematical terms. At a stroke he had proved that the heavens were not the mysterious, unknowable realm of God that many believed.

When Kepler received the string of letters from Galileo, he knew at once that it was a coded discovery and he set about unscrambling the anagram.  Galileo had already announced the discovery of four moons at Jupiter, and Kepler’s analytical mind had formed a hypothesis. If Earth had one moon and Jupiter had four, then Mars should have two moons based upon the geometrical progress where you double the previous number to gain a series (1, 2, 4, 8 etc.).

Johannes Kepler

Kepler wrestled with the anagram until he squeezed out "Salve umbistineum geminatum Martia proles." He called it a barbaric verse, and it was a letter different from the original but it served his conviction that Mars had two moons. Kepler's translation reads: "Be greeted, double knob, children of Mars." Imagine reading that in a scientific journal today!

In fact, Kepler was wrong. Galileo had caught a blurry glimpse of the rings of Saturn and had written: "Altissimum planetam tergeminum observavi" meaning "I have observed the highest of the planets three-formed."

Nevertheless, the conviction that Mars had two moons persisted for centuries. In 1726, English satirist Jonathan Swift wrote about them in Gulliver's Travels. But it wasn’t until 1877 that Asaph Hall discovered Phobos and Deimos, the two moons of Mars, from the United States Naval Observatory in Washington DC. -- Stuart

Although emphasis is being placed on 3 March, when the closest Phobos flyby ever performed will take place, it is not the only time Mars Express will be drawing near to the mysterious moon of Mars.  The 3 March flyby is simply the high point (or should that be low point?) of a six-week campaign to study Phobos in closer detail than ever before.  It all begins on 16 February, next week, when Mars Express flies past Phobos at an altitude of 991 km.

There will be three more flybys during the fortnight after that, each drawing closer than the last, until the unprecedented 50 km flyby on 3 March.  Afterwards, a further seven flybys will be performed, each at slightly higher altitudes as the spacecraft’s orbit carries it further away from Phobos. Two of them will be used to image the proposed Phobos-Grunt landing site.  The final flyby of this campaign takes place on March 26 at an altitude of 1304 km.

During each flyby, a variety of science instruments will be used to study Phobos from different scientific viewpoints.  One of the highlights will be to measure the gravity field of Phobos, which will allow scientists to understand more about the structure of the moon.

The origin of Phobos is a mystery, in fact three scenarios are considered possible.  The first is that the moon is a captured asteroid; the second is that it formed in-situ as Mars formed below it, and the third is that Phobos formed later than Mars, from debris flung into martian orbit when a large meteorite struck the Red Planet. Among other objectives, the Phobos flybys are designed to provide clues towards answering this question. -- Stuart

This is how Phobos looked on 28 July 2008 to the HRSC camera on Mars Express.  Then, the spacecraft was 351 km from Phobos.  HRSC will take new images during this new sequence of flybys. Credits: ESA/ DLR/ FU Berlin (G. Neukum)

The news is out!

On 26 January, Mars Express completed its 7777th orbit around the Red Planet, an auspicious milestone as the satellite is readied for Phobos flyby.

ESA's Mars orbiter will perform the closest-ever flyby of Phobos on 3 March 2010 (Wednesday), with closest approach (CA) at 20:55 UT (21:55 CET). The flyby, at a planned altitude of just 50 km, will collect very precise radio Doppler data to help determine the moon's gravity field more accurately than ever (click for full article in ESA website). -- Daniel

An image of Phobos acquired by the High-Resolution Stereo Camera on board Mars Express on 22 January 2007. The larger and inner of the two martian moons is seen here floating just above the martian limb. The image has been enhanced slightly to bring out the detail on the moon. Credits: ESA/ DLR/ FU Berlin (G. Neukum)

Welcome to the Mars Express Blog!

This blog is operated by ESA - the European Space Agency - as an unofficial and in-depth source of information for the general public. Click on 'Full story' for important information and disclaimer.
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We asked the team working on the Mars Express Blog to introduce themselves.

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