This just sent in yesterday evening by ESA's Olivier Witasse, the Mars Express Project Scientist, with details on PFS results from the Phobos flyby.

Credits: ESA/ASI/INAF-IFSI/PFS team 

The figure above (click for large size) shows the spectrum of Phobos acquired by the PFS instrument during the flyby on 9 January 2011 (Mars Express orbit 8974).

The x-axis represents the wave number, in other words the wavelength, in the infrared. The y-axis represents the radiance, a physical quantity proportional to the brightness. The data are in black (note the uncertainty is also shown), while the red curve is an interpolation to the data.

PFS on Mars Express detects Phobos!

The Planetary Fourier Spectrometer (PFS) on board Mars Express successfully observed Phobos during the close flyby performed on 9 January 2011. The instrument collected data in thermal and near infrared wavelengths, with a spectral resolution of ~1.3 cm-1. Phobos was well illuminated during the flyby, ensuring good quality data.

The figure shows a preliminary calibration of the spectrum of Phobos acquired during the flyby. The spectrum shows a clear absorption feature around the wave number 600 cm-1 (corresponding to a wavelength of 17 µm), which was already visible during previous flybys. This feature (and other less-pronounced absorption bands visible in the spectrum) will help investigations into the surface composition of Phobos.

The general shape of the spectrum allows scientists to deduce the surface temperature; a preliminary estimate for this observation indicates a surface temperature of ~ -57 Celsius.

Further analysis is required to improve the calibration and the calculation of the geometry for these new observations. Subsequent surface temperature and composition analysis will be carried out.

We received late yesterday the processed images from the High Resolution Stereo Camera (HRSC) science team and they are fabulous! The HRSC team have provided an excellent set of images and captions showing a 3D view of the moon and the proposed landing site of the Phobos-Grunt mission.

-- Stuart & Daniel

Note: Each of the images below links through to a high-resolution (TIFF) file.

The first image shows the geometrical relationships between Mars, Phobos, and Mars Express at the time of the sequence. Copyright ESA/DLR/FU Berlin (G. Neukum).
 

Stereo-1 channel image of Phobos: his image has been photometrically enhanced to illuminate darker areas. Resolution: 4.1 meters per pixel. Image: Copyright ESA/DLR/FU Berlin (G. Neukum).

3D Image (red-cyan anaglyph): The HRSC camera recorded images of Phobos on 9 January 2011 at a distance of 100 km with a resolution of 8.1 m/pixel. Due to the stereo viewing geometry during the flyby, a small part of the moon’s edge is only visible for the right eye resulting in an odd 3D-perception in this area. This part has been slightly adjusted for better viewing. Also, for the left eye at the left edge of the image four small data gaps have been interpolated. Image: Copyright ESA/DLR/FU Berlin (G. Neukum).

SRC Images: Superimposed on the HRSC nadir image are 7 SRC images with a resolution of about 3 m/pixel. The Super Resolution Channel images show more details of the surface of Phobos. Image: Copyright ESA/DLR/FU Berlin (G. Neukum).

Sequence of 5 HRSC-channels, orbit 8974: (left to right) stereo S1 (4.1 m/pixel), photometric P1 (8.1 m/pixel), nadir ND (3.9 m/pixel), photometric p2 (8.2 m/pixel), stereo S2 (4.3 m/pixel). Image: Copyright ESA/DLR/FU Berlin (G. Neukum).

Planned landing site of the Russian Phobos-Grunt mission: Image of Phobos with a resolution of 8.2 m/pixel in orbit 8974. The ellipses marked the previously planned (red) and currently considered (blue) landing sites for the Russian Phobos-Grunt mission. Image: Copyright ESA/DLR/FU Berlin (G. Neukum).

Further information:

Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Email: markus.bauer@esa.int
Tel: +31 71 565 6799
Mob: +31 61 594 3 954

Olivier Witasse
ESA Mars Express project scientist
ESTEC, The Netherlands
Tel: +31 71 565 8015
Email:  owitasse@rssd.esa.int

Univ.-Prof. Dr. Gerhard Neukum
Freie Universitaet Berlin
Fachbereich Geowissenschaften
Fachrichtung Planetologie und Fernerkundung
Mobile: +49 171-7647177
Telefon: +49 30 838 70579; +49 30 838 70575 (Sekr.)
Email:  gneukum@zedat.fu-berlin.de

Prof. Dr. Ralf Jaumann
Deutsches Zentrum für Luft- und Raumfahrt (DLR)
Institut für Planetenforschung, Planetengeologie
Tel.: +49 30 67055-400
Fax: +49 30 67055-402
Email:  ralf.jaumann@dlr.de
 

This note and images were just sent in from the MARSIS Team - it appears they did in fact receive some nice returns during Sunday's Phobos flyby. The instrument's 40-metre long antenna is usually used to send low-frequency radio waves towards Mars, which are then reflected from any surface they encounter.

The team wrote:

The multi-frequency sounding radar MARSIS successfully observed Phobos during the latest Mars Express science campaign on 9 January 2011.

MARSIS collected two segments of data containing 6000 individual echoes, acquired in 50 sec of operation. The distance from Mars Express to Phobos was in the range 180 to 230 km, using a frequency of 4 MHz.

The ground track covered new areas not explored by previous flybys. From a first analysis of the topography and based on previous experience, the layered appearance of the image, also called 'clutter' is caused by delayed radar reflections from the surrounding Phobos surface shape.

Fig. 1 (scroll down) shows the radargram of the first segment of the flyby. The top white line is the surface signature of Phobos, while the clutter or sub-surface contributions are the bottom ones.

Ground processing of the data for one single frame, is shown in Fig. 2 with a Signal-to-Noise Ratio (SNR) of about 18 dB. The first peak represents the Phobos surface, while the second one could be either clutter or subsurface returns. The distance between the two main peaks in time is about 5.7µs (microseconds).

Further and more accurate analysis will now be done to improve the signal to noise level and the range resolution, allowing a better science interpretation.

- The Marsis team

Figure 1

 Figure 2

A quick update from the Mars Express team here at ESOC: based on telemetry and information downloaded after the 9 January Phobos flyby, the spacecraft completed the flyby according to plan. Mars Express is healthy and the team are now waiting for science data to be downloaded over the next ten days.

The data will be passed to the various instrument teams for analysis, and, according the ESA's Mars Express Project Scientist Olivier Witasse, we expect to have the high-resolution images later in the week of 17 January. -- Daniel

Our sincere apologies to all who tried to follow the progress of Mars Express on 9 January - our system went down and was only restored this morning. :-(

To see the real-time updates from yesterday, access the ESA page in Facebook - which served as a handy if somewhat unplanned back-up platform! We will check with the Mars Express team here at ESOC later today and get an update out to you here in the blog. -- Daniel

• The final pre-flyby orbit determination was concluded earlier this week; this precise calculation of the Mars Express orbit was used to generate the commands for the flyby
• These commands include all necessary pointing and instrument instructions so that the flyby and science observations can be conducted automatically
• They were uploaded to the spacecraft this morning during a ground station pass at 07:00 UT (08:00 CET)
• Mars Express is now in an orbit with respect to Mars ranging from approximately 400 km to 10 000 km; it will pass by the centre of Phobos on Sunday at just 111 km
• On Sunday, 9 January, Mars Express will automatically slew to point instruments toward the expected direction of Phobos starting at 13:55 UT (14:55 CET) - it will stay in this pointing mode for 5 minutes and 46 seconds
• Closest approach occurs at 14:06:30.016 UT (15:06:30.016 CET)
• A few minutes later, after closest approach, it will slew back to Earth pointing and the next ground station pass, via ESA's 35m DSA-2 deep space station at Cebreros, Spain, will begin at 14:57 UT (15:57 CET). Data will be downloaded progressively over the following days(see "When can we expect first images" below)

"The simple fact that this flyby is being done automatically and with little human activity on the days around and during closest approach hides the large amount of work done by the operations team, the flight dynamics team, the mission scientists and the principle investigators to get ready. We are looking forward to a smooth flyby and some very interesting results."

Overall, it's a quiet but nonetheless exciting phase of the mission that promises to provide some excellent and valuable Phobos images and data from close up! We'll update you on Monday as soon as we hear any word from the team at ESOC.  -- Daniel

On Sunday, 9 January, Mars Express will make its closest approach to Phobos, with the spacecraft passing just 111 km above the moon's centre at 14:09 UT (15:09 CET). Of course, we all know that science is about a lot more than pretty pictures; but we can’t help ourselves can we? The first question any of us ask when we hear about a new flyby is, "When do we get the images?" We want to see Phobos, and we want to see it now!

While closest approach takes place this coming Sunday, Olivier Witasse, ESA Project Scientist for Mars Express, explains below that all things come to those who wait. I asked him when we can expect the first image? Olivier replied:

We will have to be patient! The whole Phobos data set will be downloaded to Earth by Tuesday, 18 January. The HRSC team will then process the data, and we can expect a release of images (including a 3D view) on Friday, 21 January.

The reason is that besides this Phobos event, there are other camera observations of Mars and many observations by the other Mars Express instruments. Software plans and optimises the data downlink to make sure that no instruments lose any data, and it uses the biggest data storage on board (the one for the camera) to act as a buffer when downlink capabilities are scarce. This avoids overwriting valuable data! Once the other data are safely on the ground, then Mars Express sends the camera files.

An interesting aspect of this story is that starting on 19 January, contact with Mars Express will be much reduced for five weeks. We will even loose contact for some days due to the solar conjunction, when the Sun will block our view of Mars and Mars Express. During this period, the spacecraft will be fully autonomous but perform no observations. Luckily, the Phobos close encounter occurs more than a week before and its images will be on the ground just in time! -- Stuart

Note: To help pass the time, enjoy are a pair of recent images captured in March 2010 by the HRSC.

 A coloured view of Phobos made from images taken from two different
flybys in March 2010. Credit: ESA/ DLR/FU Berlin (G. Neukum).

I caught up with Olivier Witasse, ESA Project Scientist for Mars Express, to ask him about the Phobos flybys currently taking place and specifically what science the team are chasing (the first few answers are below and full text is available after the jump). -- Stuart

How many fly-bys this time?
Every flyby campaign is different. This time, Mars Express flies within 1400 km of Phobos eight times between 20 December 2010 and 16 January 2011. However, only one flyby is very close, and that occurs on Sunday, 9 January 2011, at a distance of 111 km from the centre of the moon. This is the third closest flyby Mars Express has performed. The flyby speed will be about 3 km/s.

What is the prime objective of this fly-by?
The prime objective is to obtain high-resolution data from all remote sensing instruments, and especially to acquire what we hope will be spectacular images using the High Resoultion Stereo Camera (HRSC).

What do the camera team hope to achieve?
The HRSC camera will cover the southern hemisphere, which has not been well imaged during previous encounters. It should achieve a ground resolution of about a few metres per pixel. The emphasis will be on stereo imaging. These new data will improve the Phobos elevation model. This time, no colour data will be taken.

 Full story »

Our long-time colleague Emily Lakdawalla over at the Planetary Society blog sent in a Twitter query last night: "Would love to see a blog entry explaining more details of how the MEX orbit shifts with time."

Her question, while general, is directly related to this week's Phobos fly-by activity as precise knowledge of the spacecraft's orbit is vital for planning observations (Mars Express will zip by tiny Phobos is just a few seconds - see my earlier post below).

I passed her query to the Mars Express operations team here at ESOC, and received the following reply from Spacecraft Operations Engineer Hannes Griebel. His colleague Thomas Ormston, who also works on the Mars Webcam Blog, additionally took some time to generate a fantastic animation showing how the Mars Express orbit changes over time. First, from Hannes:

Mars Express is on a highly eccentric, polar orbit around Mars. This means that our spacecraft flies over the poles during each orbit, as can be seen in this full-orbit movie captured in May 2010.

However, due to perturbation forces, resulting chiefly from Mars' inhomogeneous gravity field as well as gravity from other celestial bodies and also from light and solar wind pressure, the orbit rotates slightly so that periapsis (point of closest approach to the planet) drifts around Mars.

This is actually a big plus, because over the course of several months, the spacecraft gets a close-up view of all regions - from the snow-covered poles over the windswept plains of the north to the heavily cratered highlands of the south. In other words, as Mars rotates beneath our 7-hour orbit, we get full close-up coverage of virtually the entire surface over time.

And, once in a while, our orbit intersects that of Phobos. The Flight Control and Flight Dynamics teams always take great care to ensure that whenever this happens, Mars Express and Phobos are never at that point of intersection at the same time (this would be sub-optimal -- Ed. :-)).

But, when the geometry is favourable and the two are going to pass close by, a carefully timed manoeuvre, provided by firing the thrusters, can bring our satellite close enough to Phobos to take pictures and other measurements of this extremely interesting moon.

More info available here: http://webservices.esa.int/blog/post/7/1084

Hi Daniel, all,

Please find attached an animation of the Mars Express orbit progression over time. The video runs from the middle of our first year at Mars, 2004, all the way through to 2011... sped up 10,000,000 times! You can see the red path of the Mars Express orbit as it swings around Mars throughout the Martian year (Earth dates are in the top right corner). Every few months this intersects with the orbit of Phobos (the inner green ring, the outer one is Deimos), giving us an opportunity for a Phobos flyby.

The lines don't always display in the correct order on this video, so sometimes it looks like we also cross the orbit of Deimos; this is just an optical illusion on the video (in reality, it orbits too far out from Mars for a close encounter with Mars Express).

Thomas, Hannes: Thanks for the excellent update!

ACCESS VIDEO

Watch the animation in your browser here, or

Download original file (AVI) here, or

Watch it in the 'Friends of ESA' page in Facebook here, or 

See it in the Planetary Society YouTube channel: 

Click for larger view

For the teams working on the Mars Express mission, one of the most important activities during the current fly-by phase is generating and refining estimates of the spacecraft's orbit, which must be as accurate as possible.

This is mandated by the fact that Phobos is really not that big - its mean radius is just 11 km - and the fly-by at closest approach happens rather quickly. It will be over in just a few moments as Mars Express zips by at around 3 km/second.

As a result, the camera and other instruments on board the spacecraft - and indeed the spacecraft itself - must be pointed in precisely the correct direction at precisely the correct time in order to get any useful results at all.

These pointings and timings, in turn, depend on knowing the spacecraft's trajectory very accurately - and estimating this is at least as much an art as it is a science.

The trajectory estimates make use of astrophysical data including the gravity of Mars and Phobos as well as data from the star trackers on board Mars Express (which provide a picture, literally, of the background star field) and radiometric data provided by the ground tracking stations that communicate with the spacecraft, currently ESA's giant 35m station at Cebreros, Spain.

Fixing the orbit is also very much a team effort involving experts from the flight dynamics team here at ESOC, the scientists who operate the instruments (including the HRSC camera and the MARSIS radar), and the flight operations team.

The next set of orbit calculations for closest approach on 9 January will be generated later today, and will be refined later in the week. -- Daniel

OK - admittedly, this has little to do with next week's Phobos flyby. But these are pretty cool! :-)

The VMC camera on board Mars Express acquired a set of images on New Year's day - 01.01.11 - which were delivered to Earth and auto-published in the Mars Webcam Blog less than 1 hour ago at 12:56 UT (13:56 CET)!

Click on the image at left or on the link below to view the complete set... -- Daniel

http://webservices.esa.int/blog/post/6/1297

A quick look back at Phobos from an HRSC image published as NASA's Astronomy Picture of the Day (APOD) on 1 December 2010. Click on image below to view full size and scroll down for caption. -- DGS

Martian Moon Phobos from Mars Express
Credit: G. Neukum (FU Berlin) et al., Mars Express, DLR, ESA; Acknowledgement: Peter Masek

Why is Phobos so dark? Phobos, the largest and innermost of two Martian moons, is the darkest moon in the entire Solar System. Its unusual orbit and color indicate that it may be a captured asteroid composed of a mixture of ice and dark rock. The above picture of Phobos near the limb of Mars was captured last month by the robot spacecraft Mars Express currently orbiting Mars. Phobos is a heavily cratered and barren moon, with its largest crater located on the far side. From images like this, Phobos has been determined to be covered by perhaps a meter of loose dust. Phobos orbits so close to Mars that from some places it would appear to rise and set twice a day, but from other places it would not be visible at all. Phobos' orbit around Mars is continually decaying -- it will likely break up with pieces crashing to the Martian surface in about 50 million years. 

Happy New Year!

Welcome back to the Mars Express Blog and some cool news for the start of 2011! Since December 2010, ESA's Mars Express has been progressively orbiting closer to Phobos as part of a fly-by phase that will see the spacecraft make 10 close passages of the enigmatic moon.

On Sunday, 9 January, Mars Express will make closest approach (CA): the spacecraft will pass just 108 km above the moon's surface at 14:09 UT (15:09 CET).

We've re-started our Mars Express Blog and will provide regular updates for the rest of this week - we'll be in touch with the MEX operations team here at ESOC as well as some of the scientists working on the mission. We'll also get updates direct from ESA's Mars Express Project Scientist Olivier Witasse. You can also follow the campaign on Twitter via @esaoperations and @esascience. -- Daniel

As this particular Phobos flyby season comes to an end, I caught up with Michel Denis, spacecraft operations manager; Nicolas Altobelli, scientist with the science ground segment; and Olivier Witasse, project scientist, to ask how it all went and what we can look forward to in the future. -- Stuart

This has been the most ambitious Phobos flyby campaign yet attempted, how did it go?

Michel Denis: “After almost 8000 orbits which have all been a bit different from each other, and after about 10 Phobos campaigns, we had mixed feelings between the old-sailor's confidence "it will be all-right, we have mastered much more complex activities already" and the juvenile excitement of the beginners "it's so close, and we must turn the spacecraft swiftly, and what happens if...?"

 Full story »

With today's flyby at 12:17 UTC (13:17 CET), the current Phobos flyby campaign will be complete.

Given the present polar and elliptical orbit of Mars Express (meaning that it orbits over the Red Planet's North and South poles and varies in altitude from fairly close to quite far away), and the near-circular and equatorial orbit of Phobos, encounters between the bodies can be expected every five months. However, the number of flybys, the geometry and the closest distances are always different.

The current campaign was unique: It stands out with a total of 12 fly-bys (more than any campaign before) and a minimum approach distance of 77 km from the centre of the moon, which corresponds to approx. 67 km from the surface (the closest flyby of any spacecraft to date).

So, what about the next campaigns? Let's look ahead to the next two flyby 'seasons.'

The next one will come in August 2010, with nine flybys within 1200 km from Phobos. The closest approach will be about 403 km over Phobos' night side, on 24 August 2010. Then, between December 2010 and January 2011, 10 flybys are planned, with the closest one coming within 96 km of the moon's dayside, on 9 January 2011. (This is, by the way, roughly four weeks before Mars passes behind the Sun (as seen from Earth), and only a few days before Mars Express science operations will stop for approximately 6 weeks due to this so-called 'Solar conjunction'.)

Quite interesting observations can be made from such distances indeed! The powerful cameras, spectrometers and other instruments on Mars Express can glean amazing details; repeated flybys will augment coverage of the surface of Phobos, help confirm or improve previous findings, complement existing data sets, and possibly even make new discoveries.

So we hope you'll stay with us as we set out to explore this mysterious, small world even further. This month's closest-ever flyby lies behind us, but the excitement is far from over. On the contrary, it has only just begun!

- Hannes Griebel and Olivier Witassse