Mars Express is currently working through its series of Phobos flybys, heading for its closest approach on 3 March 2010.  Different instruments are used on different flybys to gain different information about the mysterious moon.

ASPERA is studying the interaction between the sleet of electrically charged particles given out by the Sun, called the solar wind, and the surface of Phobos. HRSC will produce high resolution images of surface, paying particular attention to the Phobos-Grunt landing site.

MaRS will determine the Phobos gravity field allowing the internal distribution of mass to be determined. MARSIS is studying the sub-surface of Phobos, seeking indications of structure and internal composition. SPICAM, PFS, OMEGA are characterising the surface of the moon, with PFS aiming to measure the day and night side temperature. 

Digital terrain model of Phobos derived from HRSC data. Published in M. Wählisch et al., "A new topographic image atlas of Phobos", Earth Planet. Sci. Lett. (2009), doi:10.1016/j.epsl. 2009.11.003 Credits: ESA/ DLR/ FU Berlin (G. Neukum)

The full list of flybys, altitudes and instruments is as follows:

Date Altitude (km) * Instruments used during flyby

16 February 991 PFS, SPICAM, ASPERA

22 February 574 PFS, SPICAM, ASPERA

25 February 398 PFS, MARSIS

28 February 226 PFS, MARSIS

03 March 50 MaRS, ASPERA

07 March 107 HRSC, OMEGA, MARSIS, SPICAM, ASPERA

10 March 286 HRSC, OMEGA, MARSIS, ASPERA

13 March 476 HRSC, SPICAM, PFS, ASPERA

16 March 662 HRSC, SPICAM, PFS, ASPERA

19 March 848 HRSC, SPICAM, PFS, ASPERA

23 March 1341 Not used

26 March 1304 HRSC, SPICAM, PFS, ASPERA

 * Distance from the surface of Phobos

You can read a detailed rundown of the flyby campaign here. -- Stuart

Phobos observed by the HRSC. Credits: ESA/ DLR/ FU Berlin (G. Neukum) 

New webpages went online today allowing anyone to download data from the digital terrain model of Phobos created by the EuroPlanet project, hosted by the German Aerospace Center.  Images and data from the High Resolution Stereo Camera (HRSC) and the Super Resolution Channel (SRC) aboard Mars Express were used to create the three-dimensional representation of the moon. -- Stuart

More information is available here.

Hello once again from the Mars Express flight deck!

OMEGA Visible and Infrared Mineralogical Mapping Spectrometer on board Mars Express - Credits: ESA

The first of the two radio-sounding proficiency tests (see my earlier blog entry on the critical radio science experiments) was completed in the night from 22/23 Feb, and went very well. The second test is scheduled for tonight (24.02), and if no problems are encountered, then Mars Express is all set for probing the moon's gravity field with unprecedented accuracy.

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Phobos is doomed. It is gradually spiralling towards Mars and eventually could slam into the planet’s surface, leaving a large crater as its parting gift. Believe it or not, this discovery led to speculation that Phobos could be a space station launched by an advanced Martian civilization.

For the atmosphere to be responsible, Phobos would have to be hollow, like an Easter Egg. If the moon were solid rock, the atmosphere would have little effect. A hollow moon would be susceptible because it contained so much less mass. But if the moon were hollow, it could not be a natural object. 

That's no moon, it's a... no wait, it is a moon.

Credits: ESA/ DLR/ FU Berlin (G. Neukum) 

Writing in the Irish Astronomical Journal in 1964, Estonian astronomer Ernst Öpik noted that there were in fact three possible reasons for Phobos’s orbit. The first was that the observations were in error and Phobos was not spiralling inwards. The second was as Shklovsky suggested – and Öpik agreed that if it were hollow then Phobos was artificial. The third suggestion was that Mars’s gravity acted across the moon producing a so-called tidal force, which could rob the moon of energy.

Dr S. Fred Singer, an American physicist, joined forces with Öpik to investigate. Singer doubted the decay rate was as large as 5 cm per year. He was right. Sadly for the UFO enthusiasts, Phobos was found to be decaying at just 1.8 cm per year and this allowed Singer and Öpik to show that the third case is the correct one. Tidal forces are responsible for the moon slowly spiralling downwards. Star Wars fans will remember the classic line from the first movie, “That’s no moon, it’s a space station.”  For a while in the 1960s, some astronomers actually thought this might be true about Phobos. -- Stuart

"The Mars Express radio science investigators are hoping that the close approach will provide not only much better estimates of Phobos' mass but also how the mass is distributed within the moon. That is, there appear to be pockets of slightly denser material scattered through Phobos; by passing within 50 km, Mars Express may respond to those differences and the Doppler measurements will reveal where the denser material hides. There is a Mars express radio science group working on Phobos: The radio science PI (Principle Investigator) Martin Paetzold, in Cologne, and Tom Andert in Munich and Pascal Rosenblatt in Brussels who work on the data analysis and interpretation."

I thought his note was interesting in that it shows that (a) planetary radar and radio science can provide exquisitely detailed information on the internal structure of bodies in the Solar System, and (b) it shows the international character of such investigations. Yes, it's an ESA mission doing the closest-ever Phobos flyby and it's a European PI team that primarily conducts radio science (the MaRS team under Martin Pätzold at Köln University), but it's an international set of researchers who follow and keenly support this science.

The interesting thing is, understanding more about Phobos composition and theories of formation is not simply an arcane academic exercise. Phobos may, in fact, play a key role in future human exploration of the Solar System (more details after the jump). -- Daniel

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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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