The horst and graben landscape of Ascuris Planum

These images show a landscape deformed by strong tectonic activity in the area north of Labeatis Fossae in the Tempe Terra region of Mars. They were acquired by the High Resolution Stereo Camera (HRSC), operated by the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt; DLR), on board ESA's Mars Express spacecraft. Here, the results of the enormous forces that once affected the Martian crust as large magma pockets rose from below can be seen. These pockets lifted the crust upwards and triggered volcanic and tectonic activity. HRSC has been mapping the Red Planet since 2004, as part of ESA's Mars Express mission. It was developed and is operated by DLR. The area depicted is located northeast of the large volcanic region of Tharsis, where there are many other similar geological structures. The Tharsis region has a diameter of several thousand kilometres, making it almost as large as Europe. Tharsis is a magmatic bulge, approximately five kilometres tall, and was formed over the course of several billion years. During the gradual upwelling and stressing of the lithosphere by volcanic and plutonic rocks, enormous tensile stresses occurred in the Martian crust, transforming large regions into 'horst and graben' landscapes. Tempe Terra is the northernmost highland region on Mars. The landscape is characterised by numerous tectonic expansion structures, shield volcanoes and solidified lava flows. The fracture structures shown here are in the south-western foothills of the Tempe Fossae troughs, which are over 1000 kilometres long and whose characteristics can be compared to that of the Kenya Rift on Earth, which is a part of the East African Rift.

How do horst and graben structures develop?
The region shown in these HRSC images is a textbook example of horst and graben tectonics. If a rigid, brittle rock crust is stretched, for example when the ground below it is raised, the surface experiences tension. If the tensile stress rises above the tolerable limit for the rock, the crust breaks up along somewhat steeply sloping fracture surfaces and a 'fault zone' is created.

If the crust continues to expand, large blocks of rock slide down along the fracture surfaces for hundreds of metres, and even up to 1000 or 2000 metres in places. Over many millions of years, tectonic grabens develop. The regions left standing on both sides now tower above the landscape and form the corresponding horsts. The word pair 'horst and graben' have their origins in early medieval miners' German and were incorporated into many languages following geology's establishment as an 'Earth science'.

A change in the stress regime
Tempe Terra is a part of the Martian crust that must have experienced high tectonic stress over a very long period of Martian history. The grabens run mostly parallel from northeast to southwest. However, there are also grabens that cut across this primary direction. This indicates a change in the orientation of the stress field. Particularly in the south (to the left of Image 1), some fractures run almost perpendicular to the prevailing direction of the faults.

Varied landscape
In the north (to the right of image 1), the landscape has a much smoother profile. The grabens are partly filled by debris-covered glaciers, which are characteristic of all steeper slopes at these latitudes. What are referred to as 'wrinkle ridges' can be seen at the top of the image. These were formed in the Tempe Terra region by compressive stress and form a concentric ring around the entirety of Tharsis.

Erosion processes have also shaped this northern part of the region. The ejected material of a small crater (on the right of Image 1 and the upper right of the perspective view) rises like a platform above the surrounding landscape. These types of crater are formed whenever the ejecta are significantly more resistant to erosion processes than the surface rock. They form an erosion-resistant layer which, after the surrounding material has been removed, creates a plateau around the crater.

Image processing
The images were acquired by the High Resolution Stereo Camera (HRSC) on 30 September 2019 during Mars Express orbit 19,913. The image resolution is approximately 15 metres per pixel. The image centre is located at 279 degrees east and 36 degrees north. The perpendicular colour view was generated from the data acquired by the HRSC nadir channel, which is directed perpendicular to the Martian surface, and the colour channels.

The oblique perspective view was computed using a Digital Terrain Model (DTM) and data from the nadir and colour channels of HRSC. The anaglyph image, which gives a three-dimensional impression of the landscape when viewed with red-blue or red-green glasses, was derived from data acquired by the nadir channel and the stereo channels. The colour-coded image map is based on a DTM of the region, from which the topography of the landscape can be derived. The reference body for the HRSC DTM is an equipotential surface of Mars (areoid).

HRSC was developed and is operated by the German Aerospace Center (DLR). The systematic processing of the camera data was performed at the DLR Institute of Planetary Research in Berlin-Adlershof. Personnel at the Department of Planetary Sciences and Remote Sensing at Freie Universitat Berlin used these data to create the image products shown here.

The HRSC experiment on Mars Express
The High Resolution Stereo Camera (HRSC) was developed by the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt; DLR) and built in collaboration with partners in industry (EADS Astrium, Lewicki Microelectronic GmbH and Jena-Optronik GmbH). The science team, which is headed by Principal Investigator (PI) Ralf Jaumann, consists of 50 co-investigators from 35 institutions in 11 countries. The camera is operated by the DLR Institute of Planetary Research in Berlin-Adlershof.

Shaping the surface of Mars with water, wind and ice

ESA's Mars Express has imaged an intriguing part of the Red Planet's surface: a rocky, fragmented, furrowed escarpment lying at the boundary of the northern and southern hemisphere. This region is an impressive example of past activity on the planet and shows signs of where flowing wind, water and ice once moved material from place to place, carving out distinctive patterns and landforms as it did so. Mars is a planet of two halves. In places, the northern hemisphere of the planet sits a full few kilometres lower than the southern; this clear topographic split is known as the martian dichotomy, and is an especially distinctive feature on the Red Planet's surface. Northern Mars also displays large areas of smooth land, whereas the planet's southern regions are heavily pockmarked and scattered with craters. This is thought to be the result of past volcanic activity, which has resurfaced parts of Mars to create smooth plains in the north - and left other regions ancient and untouched. The star of this Mars Express image, a furrowed, rock-filled escarpment known as Nili Fossae, sits at the boundary of this north-south divide. This region is filled with rocky valleys, small hills, and clusters of flat-topped landforms (known as mesas in geological terms), with some chunks of crustal rock appearing to be depressed down into the surface creating a number of ditch-like features known as graben.

As with much of the surrounding environment, and despite Mars' reputation as a dry, arid world today, water is believed to have played a key role in sculpting Nili Fossae via ongoing erosion. In addition to visual cues, signs of past interaction with water have been spotted in the western (upper) part of this image - instruments such as Mars Express' OMEGA spectrometer have spotted clay minerals here, which are key indicators that water was once present.

The elevation of Nili Fossae and surroundings, shown in the topographic view above, is somewhat varied; regions to the left and lower left (south) sit higher than those to the other side of the frame (north), illustrating the aforementioned dichotomy. This higher-altitude terrain appears to consist mostly of rocky plateaus, while lower terrain comprises smaller rocks, mesas, hills, and more, with the two sections roughly separated by erosion channels and valleys.

This split is thought to be the result of material moving around on Mars hundreds of millions of years ago. Similar to glaciers on Earth, flows of water and ice cut through the martian terrain and slowly sculpted and eroded it over time, also carrying material along with them. In the case of Nili Fossae, this was carried from higher areas to lower ones, with chunks of resistant rock and hardy material remaining largely intact but shifting downslope to form the mesas and landforms seen today.

The shapes and structures scattered throughout this image are thought to have been shaped over time by flows of not only water and ice, but also wind. Examples can be seen in this image in patches of the surface that appear to be notably dark against the ochre background, as if smudged with charcoal or ink.

These are areas of darker volcanic sand, which have been transported and deposited by present-day martian winds. Wind moves sand and dust around often on Mars' surface, creating rippling dune fields across the planet and forming multi-coloured, patchy terrain like Nili Fossae.

The data comprising this image were gathered by Mars Express' High Resolution Stereo Camera (HRSC) on 26 February 2018.

ESA's Mars Express was launched in 2003. As well as producing striking views of the martian surface such as this, the mission has shed light on many of the planet's biggest mysteries - and helped to build the picture of Mars as a planet that was once warmer, wetter and potentially habitable. Read more about the past 15 years of Mars Express, and what the mission has discovered so far, here.

Mars Express keeps an eye on curious cloud

Since 13 September, ESA's Mars Express has been observing the evolution of an elongated cloud formation hovering in the vicinity of the 20 km-high Arsia Mons volcano, close to the planet's equator. In spite of its location, this atmospheric feature is not linked to volcanic activity but is rather a water ice cloud driven by the influence of the volcano's leeward slope on the air flow - something that scientists call an orographic or lee cloud - and a regular phenomenon in this region. The cloud can be seen in this view taken on 10 October by the Visual Monitoring Camera (VMC) on Mars Express - which has imaged it hundreds of times over the past few weeks - as the white, elongated feature extending 1500 km westward of Arsia Mons. As a comparison, the cone-shaped volcano has a diameter of about 250 km; a view of the region with labels is provided here. Mars just experienced its northern hemisphere winter solstice on 16 October. In the months leading up to the solstice, most cloud activity disappears over big volcanoes like Arsia Mons; its summit is covered with clouds throughout the rest of the martian year. However, a seasonally recurrent water ice cloud, like the one shown in this image, is known to form along the southwest flank of this volcano - it was previously observed by Mars Express and other missions in 2009, 2012 and 2015. The cloud's appearance varies throughout the martian day, growing in length during local morning downwind of the volcano, almost parallel to the equator, and reaching such an impressive size that could make it visible even to telescopes on Earth.

The formation of water ice clouds is sensitive to the amount of dust present in the atmosphere. These images, obtained after the major dust storm that engulfed the entire planet in June and July, will provide important information on the effect of dust on the cloud development and on its variability throughout the year.

The elongated cloud hovering near Arsia Mons this year was also observed with the visible and near-infrared mapping spectrometer, OMEGA, and the High Resolution Stereo Camera (HRSC) on Mars Express, providing scientists with a variety of different data to study this phenomenon.

Mars Express Detects Liquid Water Hidden Under Planet's South Pole

Evidence for the Red Planet's watery past is prevalent across its surface in the form of vast dried-out river valley networks and gigantic outflow channels clearly imaged by orbiting spacecraft. Orbiters, together with landers and rovers exploring the Martian surface, also discovered minerals that can only form in the presence of liquid water. But the climate has changed significantly over the course of the planet's 4.6-billion-year history and liquid water cannot exist on the surface today, so scientists are looking underground. Early results from the 15-year-old Mars Express spacecraft already found that water ice exists at the planet's poles and is also buried in layers interspersed with dust. The presence of liquid water at the base of the polar ice caps has long been suspected; after all, from studies on Earth, it is well known that the melting point of water decreases under the pressure of an overlying glacier. Moreover, the presence of salts on Mars could further reduce the melting point of water and keep the water liquid even at below-freezing temperatures. But until now evidence from the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument, MARSIS, the first radar sounder ever to orbit another planet, remained inconclusive. It has taken the persistence of scientists working with this subsurface-probing instrument to develop new techniques in order to collect as much high-resolution data as possible to confirm their exciting conclusion.

Ground-penetrating radar uses the method of sending radar pulses towards the surface and timing how long it takes for them to be reflected back to the spacecraft, and with what strength. The properties of the material that lies between influences the returned signal, which can be used to map the subsurface topography.

The radar investigation shows that south polar region of Mars is made of many layers of ice and dust down to a depth of about 1.5 km in the 200-km-wide area analyzed in this study. A particularly bright radar reflection underneath the layered deposits is identified within a 20-km-wide zone.

Analyzing the properties of the reflected radar signals and considering the composition of the layered deposits and expected temperature profile below the surface, the scientists interpret the bright feature as an interface between the ice and a stable body of liquid water, which could be laden with salty, saturated sediments. For MARSIS to be able to detect such a patch of water, it would need to be at least several tens of centimeters thick.

"This subsurface anomaly on Mars has radar properties matching water or water-rich sediments," says Roberto Orosei, principal investigator of the MARSIS experiment and lead author of the paper published in the journal Science.

"This is just one small study area; it is an exciting prospect to think there could be more of these underground pockets of water elsewhere, yet to be discovered."

"We'd seen hints of interesting subsurface features for years but we couldn't reproduce the result from orbit to orbit, because the sampling rates and resolution of our data was previously too low," adds Andrea Cicchetti, MARSIS operations manager and a co-author on the new paper.

"We had to come up with a new operating mode to bypass some onboard processing and trigger a higher sampling rate and thus improve the resolution of the footprint of our dataset: now we see things that simply were not possible before."

The finding is somewhat reminiscent of Lake Vostok, discovered some 4 km below the ice in Antarctica on Earth. Some forms of microbial life are known to thrive in Earth's subglacial environments, but could underground pockets of salty, sediment-rich liquid water on Mars also provide a suitable habitat, either now or in the past? Whether life has ever existed on Mars remains an open question, and is one that Mars missions, including the current European-Russian ExoMars orbiter and future rover, will continue to explore.

"The long duration of Mars Express, and the exhausting effort made by the radar team to overcome many analytical challenges, enabled this much-awaited result, demonstrating that the mission and its payload still have a great science potential," says Dmitri Titov, ESA's Mars Express project scientist.

"This thrilling discovery is a highlight for planetary science and will contribute to our understanding of the evolution of Mars, the history of water on our neighbor planet and its habitability."

Mars Express launched 2 June 2003 and celebrates 15 years in orbit on 25 December this year.

Martian Atmosphere Behaves as One

Understanding the Martian atmosphere is a key topic in planetary science, from its current status to its past history. Mars's atmosphere continuously leaks out to space and is a crucial factor in the planet's past, present, and future habitability - or lack of it. The planet has lost the majority of its once much denser and wetter atmosphere, causing it to evolve into the dry, arid world we see today. However, the tenuous atmosphere Mars has retained remains complex, and scientists are working to understand if and how the processes within it are connected over space and time. A new study based on 10 years of data from the radar instrument on Mars Express now offers clear evidence of a sought-after link between the upper and lower atmospheres of the planet. While best known for probing the interior of Mars via radar sounding, the instrument has also gathered observations of the Martian ionosphere since it began operating in 2005. "The lower and middle levels of Mars's atmosphere appear to be coupled to the upper levels: there's a clear link between them throughout the Martian year," says lead author Beatriz Sanchez-Cano of the University of Leicester, UK.

"We found this link by tracking the amount of electrons in the upper atmosphere - a property that has been measured by the MARSIS radar for over a decade across different seasons, areas of Mars, times of day, and more - and correlating it with the atmospheric parameters measured by other instruments on Mars Express."

The amount of charged particles in Mars's upper atmosphere - at altitudes of between 100 and 200 km - is known to change with season and local time, driven by changes in solar illumination and activity, and, crucially for this study, the varying composition and density of the atmosphere itself. But the scientists found more changes than they were expecting.

"We discovered a surprising and significant increase in the amount of charged particles in the upper atmosphere during springtime in the Northern hemisphere, which is when the mass in the lower atmosphere is growing as ice sublimates from the northern polar cap," adds Beatriz.

Mars's polar caps are made up of a mix of water ice and frozen carbon dioxide. Each winter, up to a third of the mass in Mars's atmosphere condenses to form an icy layer at each of the planet's poles. Every spring, some of the mass within these caps sublimates to rejoin the atmosphere, and the caps visibly shrink as a result.

"This sublimation process was thought to mostly only affect the lower atmosphere - we didn't expect to see its effects clearly propagating upwards to higher levels," says co-author Olivier Witasse of the European Space Agency, and former ESA Project Scientist for Mars Express.

"It's very interesting to find a connection like this."

The finding suggests that the atmosphere of Mars behaves as a single system.

This could potentially help scientists to understand how Mars's atmosphere evolves over time - not only with respect to external disturbances such as space weather and the activity of the Sun, but also with respect to Mars's own strong internal variability and surface processes.

Understanding the complex atmosphere of Mars is one of the key objectives of ESA's Mars Express mission, which has been operating in orbit around the Red Planet since 2003.

"Mars Express is still going strong, with one of its current key objectives being to explore exactly how the Martian atmosphere behaves, and how different layers of it are connected to one another," says ESA Mars Express Project Scientist Dmitri Titov.

"Having a long baseline of data is fundamental to our study of Mars - there's now over a decade of observations to work with. These data don't just cover a long time period, but also the entirety of Mars and its atmosphere.

"This wealth of comprehensive and complementary observations by different instruments on Mars Express makes studies like this one possible and, together with ESA's Trace Gas Orbiter and NASA's MAVEN mission, is helping us to unravel the secrets of the Martian atmosphere."

Mars Express to get major software update

Every so often, your smartphone or tablet receives new software to improve its functionality and extend its life. Now, ESA's Mars Express is getting a fresh install, delivered across over 150 million km of space. With nearly 15 years in orbit, Mars Express - one of the most successful interplanetary missions ever - is on track to keep gathering critical science data for many more years thanks to a fresh software installation developed by the mission teams at ESA. The new software is designed to fix a problem that anyone still using a five-year-old laptop knows well: after years of intense usage, some components simply start to wear out. The spacecraft arrived at Mars in December 2003, on what was planned to be a two-year mission. It has gone on to spend more than 14 years gathering a wealth of data from the Red Planet, taking high-resolution images of much of the surface, detecting minerals on the surface that form only in the presence of water, detecting hints of methane in the atmosphere and conducting close flybys of the enigmatic moon, Phobos. Today, Mars Express is in good shape, with only some minor degradation in performance, but its gyroscopes are close to failing.

Gyros gone bad

These six gyros measure how much Mars Express rotates about any of its three axes. Together with the spacecraft's two startrackers, they determine its orientation in space.

This is critical for pointing its large parabolic radio antenna towards Earth and to aim its instruments - like the high-resolution stereo camera - at Mars.

Startrackers are simple, point-and-shoot cameras that capture images of the background star field and, with some clever processing, are used to determine the craft's orientation in space every few seconds.

The rotation information from the gyros fills in the information between these snapshots and also when the trackers lose track of the stars - which can last for minutes or even hours.

"After looking at variations in the intensity of the gyros' internal lasers, we realised last year that, with our current usage, four of the six gyros were trending towards failure," says spacecraft operations manager James Godfrey.

"Mars Express was never designed to fly without its gyros continuously available, so we could foresee a certain end to the mission sometime between January and June 2019."

Engineers knew, however, from long experience with similar gyros on previous missions, including Rosetta and ERS-2, that it might be possible to fly the mission primarily using its startrackers, with the gyros only being switched on occasionally, to extend their lives.

Hacking 15 year-old code

"Flying on startrackers with the gyros mostly switched off meant that a significant portion of the 15 year-old software on Mars Express would have to be rewritten, and this would be a major challenge," says operations engineer Simon Wood.

While the spacecraft's builder provided great assistance, it was mostly up to the teams at ESA to open the code, rewrite the software, test it and prepare it for upload as soon as possible.

"We were also helped by being able to take code flown on Rosetta and transplant it into the Mars Express guidance software," adds Simon.

A massive, multi-month effort followed, involving teams from across the Agency working to develop the new software that would enable Mars Express to keep flying. This also meant significant changes in instrument science planning.

"We didn't know if such a massive revision was possible - it hadn't been done before, especially as we would be in a race against time to complete it. But faced with the almost-certain end of mission, what began as wild speculation during a tea break one afternoon last summer has led to the full rewrite now being ready to send up."

The new software was finalised earlier this year, and has undergone meticulous testing to ensure it will work as intended.

Go/No-Go

The effort came to fruition yesterday, when the mission team met for a critical go/no-go meeting with the ESA managers to get final approval to activate the new software.

The new code was actually uploaded to an area of spare memory on Sunday, but just like when your phone or tablet gets a software upgrade, mission controllers will have to shut Mars Express down and trigger a reboot to start running the new code, a critical step set for 16 April.

If all goes as expected, the mission teams will then spend about two weeks testing and reconfiguring the spacecraft to ensure everything is working as it should before resuming normal science operations.

"Similar, but much smaller fixes, have been developed in the past for other missions with old gyros, such as Rosetta, but this is certainly the most complex and extensive software rewrite we've done in recent memory," says mission manager Patrick Martin.

"Thanks to the skill of ESA's teams, Mars Express will fly well into the 2020s, depending on fuel supply, and continue delivering excellent science for many years yet.

"I look forward to seeing continued joint science campaigns between Mars Express and other Mars missions like ESA's Trace Gas Orbiter and incoming rover missions."

Green Light for Continued Operations of ESA Science Missions

ESA's Science Programme Committee (SPC) has approved indicative extensions, up to 2019-2020, for the operation of eight scientific missions. During its meeting at ESA Headquarters in Paris, on 21-22 November, the SPC approved indicative extensions for the continued operation of five ESA-led missions: Gaia, INTEGRAL, Mars Express, SOHO, and XMM-Newton. This followed a comprehensive review of the current operational status and outlook of the missions and their expected scientific returns during the extension period. The decision will be subject to confirmation towards the end of 2018. [1] The lifetime of Gaia, ESA's billion star surveyor, was extended by eighteen months, from 25 July 2019 to 31 December 2020. This is the first time that Gaia, which was launched in 2013 and originally funded for a five-year mission, has been subject to the extension process. Mars Express, SOHO, and XMM-Newton each received extensions of two years, so their operations will continue at least until the end of 2020.

The SPC extended the operations of the high-energy observatory INTEGRAL by one year, until 31 December 2019. A proposal to extend INTEGRAL until the end of 2020, as well as a proposal concerning a two-year extension of the magnetospheric plasma mission, Cluster, will be presented to the next meeting of the SPC in February 2018.

The go-ahead was also given to continue ESA's contributions to the operations of three international collaborative missions: the Hubble Space Telescope (HST), and the Interface Region Imaging Spectrograph (IRIS), which are both led by NASA, as well as the Japanese-led mission Hinode.

[1] Every two years, all missions whose approved operations end within the following four years are subject to review by the advisory structure of the Science Directorate. Extensions are granted to missions that satisfy the established criteria for operational status and science return, subject to the level of financial resources available in the science programme. These extensions are valid for the following four years, subject to a mid-term review and confirmation after two years. Extensions for operations in the period 2017-2018 were approved by the SPC in November 2016, but the indicative extension, for 2019-2020, had been deferred until the November 2017 meeting to allow the SPC to evaluate the outcome of the ESA Ministerial Council meeting in December 2016.