Skimming Phobos

Inputs from today's blog post were provided by Thomas Duxbury, an interdisciplinary scientist on MEX for the Mars moons and Mars geodesy/cartography (and also a co-investigator on the HRSC scene team), Dmitri Titov, ESA's Mars Express project scientist, and Simon Wood, from the MEX mission operations team at ESOC, ESA's European Space Operations Centre, Darmstadt, Germany.

On Thursday, 14 January, ESA’s Mars Express spacecraft will make an unusually close flyby of the largest Martian moon, Phobos, passing the surface at just 53 km at closet approach at 16:00:21 UTC (17:00 CET) on orbit 15260.

The event will mark the spacecraft’s closest flyby of the moon in 2016, and, as a point of comparison, most of the other almost-60 Phobos flybys this year will occur between several hundred up to almost 2000 km. So it’s a real skimmer!

Phobos flyby 14012016

Predicted view from MEX for the 14 Jan 2016 Phobos flyby. The centre image is the predicted perspective view of Phobos at closest approach. This shows the view along Phobos’ shorter axes and it appears smaller than the other two images, which show the view along Phobos’ longest axis. Credit: T. Duxbury

The flyby will enable Mars Express instruments, especially the HRSC – the High Resolution Stereo Camera – to see points of the moon’s surface that have not previously been observed from such a close range.

“This flyby will provide very good viewing, within 1,000 km, of an area previously not seen well,” Dmitri Titov, ESA's Mars Express project scientist. “HRSC will be taking images; the MARSIS radar and the ASPERA-3 particle instrument will operate as well to sound the subsurface and plasma environment of the moon.”

+ marks the spot

The “+” in the predicted images (see above) indicates a possible landing site for the future Russian Phobos Grunt sample return mission.

“This flyby is important as it will allow us to finally view this area on Phobos that has yet to be seen at high resolution and excellent lighting,” says Thomas Duxbury, professor in planetary science at George Mason University, USA.

In the past, Mars Express has made closer flybys, but not by much. On 29 December 2013, Mars Express flew by at just 45 km, close enough that the moon’s gravity pulled the spacecraft slightly off its course, enabling new estimates of the Phobos mass and density.

Phobos 2010

Phobos as seen by the HRSC nadir channel during Mars Express Orbit 7926 in 2010. Credit: ESA/DLR/FU Berlin (G. Neukum)

The flyby is an operational challenge as well as a scientific opportunity, as the positions of the moon and Mars Express must be known very, very precisely in order to safely make the ‘skim-by’.

Commands on board

Commands to trigger the instruments’ observations were uploaded  Thursday, 7 January, following last-minute optimisation of the expected position of Phobos relative to the spacecraft provided by the flight dynamics team at ESOC , Darmstadt.

“This is needed due to the high level of precision required to target Phobos with the instruments at such a close distance,” says Mars Express Spacecraft Operations Engineer Simon Wood.

“The activity will then take place fully automated and without intervention by the operations team at ESOC, who will be closely monitoring the flyby.”

Deciphering Phobos

Flybys such as this help generate evidence to understand how the moon was formed.

The mass of Phobos is estimated as 1.0603 x 10^16 kg (uncertainty less than 0.5 %) and the density is 1862 kg/m3 (uncertainty less than 2%). For comparison, the density of Mars is about 3930 kg/m3, and Earth has a density of around 5520 kg/m3.

The low density of Phobos is consistent with the moon having a high porosity with an uneven mass distribution; in other words, it is essentially a rubble pile with large empty spaces between the rocky blocks that make up the moon’s interior.

This favours the formation scenario in which Phobos was born in orbit around Mars from a disc of debris and is not a captured asteroid – one of the other leading theories for how Phobos and its sibling Deimos came into existence.

Mars Express in orbit around Mars. Credit: ESA/AOES Medialab

Mars Express in orbit around Mars. Credit: ESA/AOES Medialab

The debris disc could have resulted from a large impact on the surface of Mars, or perhaps Phobos (and maybe Deimos) formed from left-over debris from the formation of Mars itself.

Data from such flybys will also prove valuable in planning future robotic or even human missions to land on the moon, and ideal location from which to observe Mars.

It is expected that the initial results from this flyby will be available in the coming weeks.


Editor's comment: It is interesting to note that, because the polar orbit of Mars Express intersects the equatorial orbit of Phobos, at some point in the future – long after Mars Express has depleted its fuel and has been shut down – the spacecraft is likely to impact the moon.

ESA Mars Express HRSC images now available under a Creative Commons licence

Editor's note: This is cross-posted from ESA's new Communication blog; the original was published earlier today by Marco Trovatello.

Following its arrival at the Red Planet in December 2003, imagery from ESA’s Mars Express mission has proved immensely popular, with the High Resolution Stereo Camera (HRSC) on board the spacecraft playing a major role.

Since January 2004, ESA and its partners at the German Aerospace Center (DLR) and the Freie Universität Berlin (FUB) have been jointly publishing colour, stereo pictures of the martian surface from orbit, both still and moving. For example, a “Mars showcase” video, comprised of HRSC images, has been viewed almost 700,000 times since it was published on ESA’s Youtube channel in 2013.

But starting today, something is different with these regular image releases: in a joint undertaking by all three partners, Mars Express HRSC images will be made available under a Creative Commons (CC) licence. The licence we will apply is the same one we recently introduced for Rosetta NAVCAM images: CC BY-SA IGO 3.0, with credit to ESA/DLR/FU Berlin. In practical terms it will look like this:

Hellas Chaos

Hellas Chaos on Mars. Image Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

And as luck would have it, we have a Mars Express HRSC movie release today which becomes the first to be covered by this Creative Commons licence:

Please read the full article on the ESA web portal here.

The licence will also be applied retroactively to all HRSC images released to date. As with Rosetta NAVCAM images, please bear with us as it will take a while to go back and change the credit lines for all of those images in our online galleries. But as a start, we have applied the new licencing to all HRSC images in our Mars Express Flickr album.

While at ESA we have only just begun releasing content under Creative Commons licences, our partners at DLR have been using CC as their standard licencing policy since 2012. Nevertheless, there is still something just a little bit special about the news today: as far as we know, it is the first time that three public organisations in Europe have teamed up in licencing a batch of joint content under Creative Commons.

For more in-depth info on ESA’s implementation of the CC BY-SA 3.0 IGO licence, please also read this blog post that I wrote with my colleague Mark McCaughrean.

Comet Siding Spring imaged by HRSC on board Mars Express

Comet Siding Spring came extraordinarily close to Mars as it whizzed by on 19 October 2014. The celestial body – a mere 500 metres in diameter – passed the Red Planet at a distance of just 137 000 kilometres, where it was observed by several spacecraft in orbit around Mars. The High Resolution Stereo Camera (HRSC), operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) on board ESA's Mars Express, also acquired a series of images with its SRC channel during Mars Express orbit 13710.

This animation combines multiple images that were acquired by the HRSC camera on board Mars Express during the comet Siding Spring flyby on 19 October 2014. Credit: ESA/DLR/FU Berlin

This animation combines multiple images that were acquired by the HRSC camera on board Mars Express during the comet Siding Spring flyby on 19 October 2014. Credit: ESA/DLR/FU Berlin

As it flew by, Siding Spring was travelling at a velocity of around 56 kilometres per second relative to Mars. Images were acquired at 17-second intervals; the spatial resolution is 17 kilometres per pixel. The images show the comet nucleus as well as the surrounding dust and gas cloud (coma).

Comet Siding Spring originates from the Oort Cloud, a comet ‘reservoir’ in the outer reaches of the Solar System. The comet was named after the Australian Observatory at which it was originally discovered back in 2013, and has the scientific designation C/2013 A1. As comets approach the Sun, one or two tails composed of gas and dust or ionised gases form on the side facing away from the Sun. As it whizzed by the planet, Siding Spring’s tail penetrated the Martian atmosphere, where it was analysed by the particle detector ASPERA-3 on board Mars Express, among others.

Scientists hope to use the data acquired, as well as the spectrometer measurements conducted at the same time, to gain an insight into the comet’s composition. It is thought that comets may contain material dating back to the formation of the Solar System.

10 years of imaging Mars

Today's post – part of a series of reports marking the MEX 10th anniversary – was submitted by the Mars Express imaging team at Freie Universität Berlin - Ed.

Who would have thought, 10 years ago, that the brave MEX spacecraft would be still alive today?

For 10 years, the High Resolution Stereo Camera (HRSC) onboard Mars Express has provided astonishing images of the surface of Mars in colour and in 3D. From the beginning on, the breathtaking colour images from Mars delighted both the public and the scientists.

For scientists, the Digital Elevation Models (DEMs) derived from the stereo images provided a major step forward in the precise analysis of the martian surface, and the wide and long image swaths give excellent overviews of the terrain and its geological context.

HRSC image of Valles Marineris, the Solar System's grandest canyon!
Credits: ESA/DLR/FU Berlin (G. Neukum)

The public also made use of the HRSC data, not only from our Press Archive where the best images of the returned data are presented, but for example also using HRSC data in the Google Earth-Mars interface. Bit by bit, Mars turns into HRSC colour. Very much appreciated were also the HRSC-movies, created with the Digital Elevation Models and including, for example, a fly-through of the "Grand Canyon" of Mars, Valles Marineris.

Throughout the last decade the HRSC team has recorded 95.5% of the martian surface at a resolution of 60 m/pixel or better and 66.8% with a resolution of 12.5-20 m/pixel.

Due to the elliptical orbit of Mars Express, major challenges had to be mastered concerning the processing of the data and the photogrammetry. Furthermore, much patience was required due to dust-storms and clouds in the atmosphere, which reduced the data quality. Therefore, several regions were targeted multiple times.

Comparing the first images recorded by HRSC with those acquired today, there is no question that with improved image processing techniques the quality of image and DEM products have very much improved over the past 10 years .

The success story of Mars Express continues and we look forward to fully image the Red Planet with HRSC at highest resolution.

Happy Birthday Mars Express!!

Student of Mars

Today's post – part of a series of reports marking the MEX 10th anniversary – was submitted by planetary geologist Damien Loizeau, who is on the hunt for water on Mars - Ed.

Damien Loizeau

I got involved in Mars Express when I started my PhD. Mars Express had been in orbit for a bit more than a year, the first results had just been published, and lots of new and exciting data were transmitted every week. Now I am part of two instrument teams for the mission: OMEGA, the imaging spectrometer, and HRSC, the high resolution stereo camera.

I work on the geology of the surface of Mars and these two instruments are perfect to study it. OMEGA helps us to determine the mineralogy of the surface, that is, the composition of the rocks, and we try to understand the age and the formation of the geological units with HRSC.

It was the first time that we had such a large dataset to understand the geology of Mars, and I was starting my scientific career inside this flow of new discoveries.

I could meet many of the leading European and American Mars scientists during the Mars Express instrument team meetings, where the most recent discoveries were presented and discussed. I also had the chance to work directly with the principal investigators of OMEGA and HRSC, in Orsay (France) and Berlin (Germany), respectively.

My first focus was on identifying minerals formed with liquid water. Liquid water is crucial for life on Earth, and it’s of utmost importance to evaluate if Mars was habitable, and if life had a chance to develop there. We mapped clays in different regions of Mars with OMEGA. On Earth, clay minerals mainly form over long periods by the interaction of rocks with liquid water. With the help of the orbiting high resolution cameras like HRSC, we observed that almost all the clay detections corresponded to rocks formed in the very early Martian history. This is a major sign of the drastic climate change that the Red Planet suffered more than 3 billion years ago.

I had the opportunity to make the map below for one of the Mars Express press conferences to illustrate our work, and I have been very happy to see it circulating on the web and in conferences for many years since.

Perspective view of clay-rich rocks (blue) on the old plateaus around the valley of Mawrth Vallis (left) and the crater Oyama (centre), made from a compilation of OMEGA, HRSC and MOLA (NASA Mars Global Surveyor) data. Credits : ESA/OMEGA/HRSC

Lately I had the opportunity to work for two years in one of ESA’s centres – ESTEC – in the Netherlands. I could follow more closely the missions with the scientists in charge of them, and the future projects like ExoMars. It was quite different from the academic world, with lots of new acronyms to remember!

Today, with the help of the instruments of the NASA Mars Reconnaissance Orbiter, we are discovering the diversity of environments were liquid water has been present in the past on Mars, not only at the surface, but also at kilometre depths. But there is still a lot to discover both within the datasets from the spacecraft still in orbit around Mars, and from future missions. Exciting times lie ahead!

Gale Crater in 3D

Gale Crater in 3D as seen by Mars Express! Next visitor? Curiosity!

Gale Crater in 3D Credits: ESA/DLR/FU Berlin (G. Neukum)

Gale Crater in 3D Credits:Gale Crater is 154 km wide and is located at latitude 5.4 degrees south and longitude 137.9 degrees east. This image, taken by the High Resolution Stereo Camera (HRSC) of Mars Express, has a resolution of 100 metres per pixel. It is colour-coded based on a digital terrain model derived from stereo image data. Credits: ESA/DLR/FU Berlin (G. Neukum).