A Swiss Camera Goes to Mars1

Home , Giotto (spacecraft), Talking About Life

INTERNATIONAL SPACE SCIENCE INSTITUTE SPATIUM Published by the Association Pro ISSI No. 40, November 2017

173449_Spatium_40_2017_(001_016).indd 1 31.10.17 11:40 Editorial

When I am in Rome, a visit to Could our home planet eventually Campo dei Fiori is one of my pri- take the same route as Mars? The Impressum orities. The place is a charming search for life on Mars helps un- venue today where farmers offer derstand its history and no less that fragrant flowers, vegetables and the of our home planet. like, while some 400 years ago, one ISSN 2297–5888 (Print) of humankind’s most courageous The current issue of Spatium pays ISSN 2297–590X (Online) thinkers payed for intellectual free- homage to one of the teams rush- dom with his life. ing after some of the elusive signs of Martian life that research could Spatium On a cold winter day in February get hold of so far. It was merely a Published by the 1600, a handful of menials pile little trace gas in its atmosphere. Association Pro ISSI firewood on Campo dei Fiori. Yet, it convinced the European They prepare the stake for a hag- Space Agency to implement a gard Dominican priest, who has dedicated mission to Mars and the passed the last seven years in near- scientists at the University of Bern by Castel Sant’Angelo’s muggy to bring forward a cutting-edge Association Pro ISSI prisons. His misdoing is to fancy camera to find out where the trace Hallerstrasse 6, CH-3012 Bern there could be an infinite Universe gas comes from. We are proud to Phone +41 (0)31 631 48 96 and uncountable civilizations out present our readers herewith the see there. To the Roman inquisition, summary of Professor Nicolas www.issibern.ch/pro-issi.html this is a clear case of heresy. The Thomas’ fascinating report for the for the whole Spatium series next day, on 17 February, Giordano Pro ISSI audience on 8 June 2016. Bruno dies in the flames. His brav- Meanwhile, their camera has made President ery, however, grants him immor- the first fly-by around Mars con- Prof. Adrian Jäggi, tality in humanity’s history. firming the anxiously waiting University of Bern team in Bern its perfect function- Times have changed a little bit: ality to start the scientific mission Layout and Publisher those, who dream of extra-terres- in March 2018. If there is any life Dr. Hansjörg Schlaepfer trial life and participate in its dis- there, they should find it! CH-6614 Brissago covery, enjoy the great public’s ad- miration today. Hansjörg Schlaepfer Printing Brissago, October 2017 Stämpf li AG When it comes to the search for CH-3001 Bern alien life, Mars plays a prominent role. The current view is that this planet was very life-friendly in its early days, and that life may have emerged there more or less simul- taneously, as it did here on Earth. Unfortunately, however, the Red Planet took another way in its evolution than our Blue Planet: Mars became cold and dry, hostile to any life on its surface, while on Earth, every corner brims over with ani- mate beings. Why that difference?

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173449_Spatium_40_2017_(001_016).indd 2 31.10.17 11:40 CaSSIS: A Swiss Camera Goes To Mars1

By Professor Nicolas Thomas, University of Bern

When it comes to searching for ther direct research to these spe- Introduction present or extinct life, the first step cific parts of the planetary surface. is the detailed mapping of the plan- This is exactly the mission ob jective etary surface. This applies not only of the European Space Agency’s This issue of Spatium is devoted to to the topography, but also to the Trace Gas Orbiter, of which one Mars, Fig. 1. The careful reader detection and location of any pos- of the instruments is the Colour might remark to his surprise that sible traces of life, such as for in- and Stereo Surface Imaging Sys- it is not the first time that Spatium stance waste products. To this end, tem, CaSSIS. is about the Red Planet2. Yet, there one looks for the outcome of the are valuable reasons for doing so: terrestrial organisms’ metabolism Much progress has been made in firstly, amongst all cosmic objects, in the hope that in an alien world the last few years; so it is no won- Mars stands out as being the near- similar forms of life would produce der that Spatium addresses Mars est planet to Earth. This facilitates similar waste products. Here, trace again. The reader will gladly no- its exploration; it may even allow gases come into play; these are gas- tice that there are many further exploration by humans in the near eous components of the atmos- good reasons to do so, be it only future. Secondly, its surface condi- phere in minute concentrations. If the fact that Swiss scientists and en- tions are the most similar to those such gases of potentially biologic gineers are proudly contributing on our home planet and they may origin can be found, the next step systems that are currently investi- have been even more so in the dis- is to pinpoint their sources to fur- gating the Red Planet … tant past. Last but perhaps most importantly, Mars is also the nearest celestial body that might harbour Fig. 1: Earth and Mars compared: The Red Planet is roughly half the size of our some forms of life3 (or may have home planet with a mass of about 12% of the Earth’s. It circles the Sun on an orbit about 50% larger, which translates into a solar irradiation of some 43% as compared done so in the past). to Earth. The Red Planet has practically no atmosphere; the iron oxide on its surface provides it a tawny tint. In contrast, Earth has a relatively dense atmosphere Other hot spots in the solar system and oceans giving a bluish shading. (Credit: NASA, Jet Propulsion Laboratory) that might offer suitable conditions for life are in the oceans under the thick ice sheet on Jupiter’s moon Europa, or even more speculatively, under the ice cover of Enceladus, a Saturnian satellite. Much, much farther out, some of the innumer- able planets circling stars other than the Sun might equally be capable of harbouring life. Yet, the exploration of those distant worlds poses technical challenges that are far greater than exploring the Red Planet.

1 The text constitutes a free interpretation of Prof. Thomas’ lecture for the Pro ISSI audience on 8 June 2016. It was drafted by Dr. Hansjörg Schlaepfer and revised by Prof. Thomas. 2 See for instance Spatium no. 5: Earth, Moon and Mars by Johannes Geiss, June 2000. 3 When talking about life in the present context, we have complex organisms in mind that are similar to what we find on Earth in that their cells contain water as the key solvent. This definition is by far not conclusive; indeed, nothing is trickier than the definition of life including possible extra-terrestrial forms (see also Spatium no. 16: Astrobiology by Oliver Botta, July 2006).

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173449_Spatium_40_2017_(001_016).indd 3 31.10.17 11:40 lution as compared to Earth’s. The To summarize, Mars has passed A Brief History planets formed by collisions with through different evolutionary of Mars and incorporation of increasingly phases: some areas show strong larger chunks of material. This pockmarks by impact craters, process caused the emerging plan- while others are smooth and plane. ets to absorb much kinetic energy, Since the estimation of the age of In order to understand the scientific which as heat energy made them a surface usually takes into account rationale for assuming present or melt. Later, when the bombard- the density of impacts on a particu- extinct life on Mars, one has to look ment ceased, the bodies began lar area, the diversity in crater den- back at the planet’s early history. cooling down. Mars, due to its sity suggests different ages of the Like all the planets in the solar sys- smaller mass, cooled faster than various parts of the planetary sur- tem, Mars evolved 4.6 billion years Earth. Therefore, from a geologic face. Consequently, Martian his- ago from a huge disk of dust and point of view, Mars is probably a tory can be divided into four dis- gas4 from which, in its very centre, dead planet today: there are no tinct epochs as described below: the young Sun emerged. This huge plate tectonics and even the solar central body acquired some 98% of system’s largest volcano, Olympus the disk’s mass while leaving the re- Mons, ceased erupting millions of The Pre-Noachian6 maining debris to the emerging years ago. This is an essential as- (4.6–4.1 billion years ago) planets and all the other bodies pect as tectonic activity with its making up the solar system. The volcanism and the consequent at- Mars emerged from the protosolar Sun acquired sufficient mass to pro- mosphere appears to be an indis- nebula 4.6 billion years ago. It con- duce a gravity field strong enough pensable requisite for the evolution tinued acquiring mass as a result of to ignite nuclear fusion processes in and subsistence of life on a planet5. impacts with bodies crossing its or- its core, in which, initially, two The CO₂ atmosphere of Mars is bit during the first ~500 million hydrogen nuclei combine to one relatively low pressure (around years. Even at this time, Mars prob- helium nucleus thereby releasing 1/150th of the Earth’s atmospheric ably began developing an atmos- tremendous amounts of energy. pressure) and consequently wide phere by impact-related outgassing This made the Sun shine. surface temperature swings from from the planet’s mantle. As im- –133 °C lows up to 25 °C highs are pact rates decreased, the tempera- While Earth circles the Sun at a evident precluding water-based life ture fell, allowing atmospheric wa- distance of 150 million km, the on its surface most of the time. ter vapour to condensate and rain Red Planet’s orbit is some 50% out to form vast oceans. With fur- larger than Earth’s. This greater In contrast, in its early days, when ther cooling, a first window opened orbit leads to lower solar irradia- Mars still had enough heat energy, for the possible emergence of life tion and a climate generally colder it must have possessed a denser at- in the Martian oceans around 4.4 than Earth’s. Mars is about half the mosphere allowing liquid water to to 4.3 billion years ago. diameter of the Earth, which trans- exist on its surface, probably in lates into a mass ratio of about 1:8. great quantities as some topologic This smaller mass of Mars is a key features (river beds, gullies, etc.) to understanding its dissimilar evo- suggest.

4 See Spatium no. 6: From Dust to Planets by Willy Benz, October 2000. 5 See Spatium no. 30: Planets and Life by Tilman Spohn, October 2012. 6 The name Noachian stems from Noachis Terra (lit. “Land of Noah”), a heavily cratered highland region west of the Hellas basin.

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173449_Spatium_40_2017_(001_016).indd 4 31.10.17 11:40 The Noachian gases into the atmosphere includ- surface conditions continued to be (4.1–3.7 billion years ago) ing water vapour, which rained out favourable for the emergence of to erode the valley networks we life. The Noachian includes the period still can see today in many basins of the Late Heavy Bombardment and craters. The Hesperian once again with numerous asteroid (3.7–2.9 billion years ago) and comet impacts, Fig. 2. The Hel- Because the planet cooled rapidly, las, Isidis and Argyre basins, the the magnetic dynamo shut down7: The Hesperian8 period was rela- largest impact structures still visi- Mars lost its global magnetic field. tively calm with fewer impacts ble on the planet, are the result of This paved the way for a thinning compared to the Noachian. It con- these events, as well as many of the of the atmosphere by high ener- stitutes the interim phase between craters that characterize the south- getic particles from space that the humid, warm climate of the ern highlands. could now strip away atmospheric Noachian and the subsequent cold molecules. Habitable environ- and dry phase we see on Mars At the same time, large-scale vol- ments gradually became smaller today. canic eruptions poured ash and and more localized, but Noachian During the Hesperian, there was still considerable volcanism, albeit Fig. 2: Colorized relief map of Noachis Terra. Colours indicate elevation, with at a slowing pace. Volcanoes re- red highest and blue-violet lowest. The blue feature at bottom right is the north- western portion of the giant Hellas impact basin. (Credit: NASA, Arizona State leased large amounts of sulphur University) dioxide and water; the gases re- acted to make sulphuric acid, which then rained onto the surface. As a result, the Hesperian is characterized by extensive sul- phate deposits.

Valley network formation waned as the climate became colder and much of the water was probably locked up as permafrost or subsurface ice. Episodically, impacts hit the surface thereby heating the ground ice and subsurface water. This gave rise to catastrophic, yet short-lived, floods creating huge outflow channels along with the formation of so-called chaotic terrain (See Fig. 3 on the next page).

7 Like Earth, Mars is differentiated, that is, it has a dense metallic (iron) core overlain by a rocky (silicate) mantle. The spinning hot and magnetized iron core creates a magnetic dynamo. This gives rise to electrical currents within the core that generate the planet’s global magnetic field. This field deviates energetic particles from space preventing them to hit the planet’s atmosphere and surface. 8 The Hesperian period is named after Hesperia Planum, a moderately cratered highland region northeast of the Hellas basin.

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173449_Spatium_40_2017_(001_016).indd 5 31.10.17 11:40 Fig. 3: Kasei Valles. Kasei, the Japanese name for Mars, constitute the longest valleys on the Red Planet. They start in a chaotic region and divide into several arms. This system probably formed because of episodic floods with huge amounts of water masses seeking their way down to the Chryse Planitia lowlands. The waters are thought to have been released by melting subsurface processes heated by tectonic activities or asteroid impacts. (Credit: NASA, JPL-CalTech, Arizona State University)

Amazonian Late-stage volcanism included the There is increasing evidence that (2.9 billion years ago to last eruptions of Olympus Mons Mars experiences long-term cli- present) and widespread lava flows else- mate cycles that have a significant where. Meanwhile, aeolian (wind) influence on the distribution of The Amazonian9 period is charac- erosion and deposition shaped large ices. Such long-term climate cycles terized by the absence of large- areas of Mars, notably the broad may take place over thousands to scale geological and climatic plains and sand dunes near the millions of years as the axial tilt of changes. For much of the period, poles. the planet and its distance from the the planet’s surface has been dry Sun undergo cyclical changes. and cold.

9 The Amazonian period has its name from Amazonis Planitia, which has a sparse crater density over a wide area.

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173449_Spatium_40_2017_(001_016).indd 6 31.10.17 11:40 The Red Planet Martian sky a tawny reddish hue imply that it is released from dis- when seen from the surface. It crete regions. Currently, there are Today would also be noticeable to some- three such areas, of which the most one on the surface that the bright- important plume features some ness of the sky is highly non-uni- 19,000 metric tons of methane, form – unlike on the Earth where with an estimated source strength Even though Mars is very differ- a cloudless sky is uniformly blue to of 0.6 kilograms per second. ent from our world, it is neverthe- a first approximation. This high- less the planet resembling our lights a fundamental difference be- Secondly, observational data suggest Earth the most. Its present climate, tween the two planets. On Mars, that water once flowed over these however, makes it more than ques- dust scatters light in the atmos- regions, which could have sup- tionable whether there is still ac- phere whereas on Earth it is mostly ported the emergence of life there. tive life on the Martian surface. In- the gas molecules that do the deed, none of the rovers inspecting scattering. Thirdly, most challenging is the fact sites could identify any trace of that in the Martian atmosphere current life to date. However, life methane has a life expectancy of could still be active below the sur- Methane 50–200 years. Thus, its presence face where warmer aquifers might requires an active source that com- allow water to remain liquid the Methane is one of the many trace pensates for the losses incurred by entire Martian year round and of- gases in the Martian atmosphere. dissociation. fer shelter against the deadly high- Yet, it causes a disproportionate in- energy radiation from space10. terest amongst scientists, as on One of the hypotheses to explain Earth, this gas is mostly the prod- these observations is that under- uct of biological and anthropo- ground liquid water areas would The Atmosphere of Mars genic processes. (Since the indus- be able to provide a habitat for mi- trial revolution Man has had a croorganisms, which release meth- Compared to Earth, the actual at- significant impact on atmospheric ane as a waste product. If the meth- mosphere of Mars is extremely methane concentrations, increas- ane is of biological origin, two thin. Atmospheric pressure on the ing them by roughly 250%.) It is scenarios may apply: surface ranges from a low of 30 Pa also well-known as an important on Olympus Mons to over 1,155 greenhouse gas. The methane 1. Long-extinct microbes, which Pa in Hellas Planitia, with a mean found on Mars, so the speculation disappeared millions of years pressure of 600 Pa. The resulting goes, could therefore be of biolog- ago, have left the methane fro- mean surface pressure is only about ical origin as well indicating the zen in the Martian upper sub- 0.6% of that on Earth. presence of life beneath the surface, and this gas is released surface. into the atmosphere today as The chemical composition of the temperatures and pressure near thin Martian atmosphere is also Several observations underpin this the surface change, or quite different to the Earth’s. It is hypothesis. 2. Some very resistant methane- composed mostly of carbon diox- producing organisms still sur- ide, whereas the Earth’s atmos- Firstly, methane occurs in the Mar- vive. One way to confirm the phere holds some 78% nitrogen. Its tian atmosphere in extended biological origin of methane atmosphere is dusty giving the plumes only, the profiles of which would be to measure the isotope

10 Recently, scientists found complex multi-cellular organisms in depths down to 3.6 km in the deep mines in South Africa, see Nature 474, 79–82, (02 June 2011). These may be analogous habitats as those subsurface aquifers on Mars.

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173449_Spatium_40_2017_(001_016).indd 7 31.10.17 11:40 ratios of carbon and hydrogen, The European ogies paving the way for a future the two elements of methane. Mars sample return mission in the Life on Earth tends to use lighter Space Agency’s 2020’s. isotopes, for example, more 12C than 13C, because this requires ExoMars The ExoMars programme contains less energy for bonding. Yet to two missions carried out in coop- answer this question, scientists Programme eration with Roscosmos12: must first get hold of some sam- ples of the Martian methane. ––The 2016 mission consists of the In the framework of the ESA Cos- Trace Gas Orbiter (TGO) in- While the hypothesis of a connec- mic Vision11 programme, there is a cluding a landing demonstrator tion to active biology is highly in- theme devoted to planets and life module, and triguing, it is important to note entitled “Life and Habitability in ––The 2020 mission includes a that other sources (e.g. volcanism) the Solar System”. Under this title, rover that will carry a drill and a might also contribute to the meth- ESA runs the ExoMars Programme suite of instruments dedicated to ane budget. 2016–2020 addressing the question exobiology and geochemistry of whether life ever existed on research. Mars and preparing new technol- Summary

Evidence suggests that Mars was Fig. 4: The Trace Gas Orbiter in an artist’s impression. Clearly visible are the significantly more habitable dur- very large solar panels required for providing the spacecraft with enough electrical energy under the reduced solar illumination conditions at the Martian orbit. (Credit: ing early epochs than it is today. ESA) Life may have emerged in the distant past as it did on our own planet. Yet, whilst on Earth conditions for life remained more or less favourable for the subsistence of life, dramatic climate changes followed on Mars that make the surface a hostile environment today. Yet, by analogy to findings on Earth, life may still be active below the surface for which the methane plumes could act as pre- cious signposts. Advancing our knowledge regarding these potential sites of life is the key goal of the European Space Agency’s Exo Mars programme, which we are going to address now.

11 Cosmic Vision is the name of the current phase of ESA’s Science Programme. 12 Roscosmos is the space agency of the Russian Federation.

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173449_Spatium_40_2017_(001_016).indd 8 31.10.17 11:40 The ExoMars Trace Gas ––CaSSIS: The Colour and Stereo neutron detector that can pro- Orbiter Surface Imaging System is a vide information on the presence high-resolution, 4.5 m per pixel of hydrogen, in the form of wa- The Trace Gas Orbiter, Fig., 4 car- colour stereo camera for taking ter or hydrated minerals, in the ries a scientific payload capable of images in natural colours and for top one meter of the Martian detecting and characterizing vari- the production of accurate digi- surface. This package is a contri- ous trace gases in the Martian at- tal elevation models of the Mar- bution from the Space Research mosphere. It will also investigate tian surface. This camera is a Institute (IKI) in Moscow. the location and nature of the contribution by the University of sources that produce these gases. Bern together with Italian and FREND measures the flux of neu- To cope with these objectives, the Polish partners. trons from the Martian surface. TGO carries the following four in- These neutrons are produced by struments aboard: ––FREND: The Fine-Resolution Epi- the continuous cosmic ray bom- thermal Neutron Detector is a bardment that interacts with the ––NOMAD: The Nadir and Occulta- tion for Mars Discovery combines three spectrometers (two in the Fig. 5: Artist’s impression of the ExoMars 2016 Trace Gas Orbiter seen from infrared and one in the ultravio- the planet-facing side. The four instruments (CaSSIS, NOMAD, FREND and ACS) are mounted on the exterior of the spacecraft to facilitate undisturbed obser- let spectrum) to perform high- vation of the planet’s surface. To the right is Schiaparelli, the entry, descent and sensitivity orbital identification landing demonstrator module. The large solar arrays are partially cut away to high- of atmospheric components via light the spacecraft’s body. (Credit: ESA) both solar occultation13 and direct reflected-light nadir obser- vations14. The Belgian Institute for Space Aeronomy is responsi- ble for this instrument.

––ACS: The Atmospheric Chemistry Suite consists of three infrared instruments that help investigate the chemistry and structure of the Martian atmosphere. ACS complements NOMAD by ex- tending the coverage at infrared wavelengths and by taking images of the Sun to better analyse the solar occultation data. This package is a contribution from the Space Research Institute (IKI) in Moscow.

13 The term solar occultation refers to an operational mode, whereby the instrument looks toward the Sun and examines the composition of the sunlight that passes through the atmosphere. The atmospheric gases partially occult the sunlight at specific wavelengths thus allowing the instrument to determine the local chemical composition of the atmosphere. 14 The term reflected-light nadir designates a mode whereby the instrument looks directly downward toward the surface and observes the sunlight scattered by the atmospheric constituents. This is a complementary way of analysing the composition of the atmosphere.

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173449_Spatium_40_2017_(001_016).indd 9 31.10.17 11:40 first few metres of rock. The cos- The ExoMars programme will fol- programme (the Principal Investigator mic rays are sufficiently energetic low with the Surface Science Plat- in the space argot) together with to break apart atoms, releasing form and the ExoMars Rover in the Co-Principal Investigator Ga- high-energy neutrons that are then 2020. For these probes as well as briele Cremonese of the Astro- slowed down and absorbed by the for NASA spacecraft, the TGO nomical Observatory of Padua, nuclei of elements in the surround- will operate as a communication Italy. ing material. Not all the neutrons link with Earth until 2022. are captured though, many escape, Specifically, CaSSIS serves to: creating a leakage flux of neutrons that the FREND instrument will The Colour and Stereo ––Characterize the sites, which observe. The distribution of neu- Surface Imaging System have been identified as potential tron velocities, which depends (CaSSIS) sources of trace gases. upon how much they were slowed ––Investigate dynamic surface pro- down before escaping, can reveal In order to locate potential sources cesses (e. g. sublimation, ero- much about the surface material of trace gases on the planetary sur- sional processes, volcanism) since it depends on the composi- face as well as to qualify potential which may contribute to the at- tion of that material, primarily on sites for future landes missions, a mospheric gas inventory. its hydrogen content. The hydro- high-resolution camera is required. ––Certify potential future landing gen serves as an indicator of the This is the scope of CaSSIS, pro- sites by characterizing local presence of water. posed by Prof. Nicolas Thomas and slopes, rocks, and other latent his team at the University of Bern. hazards. He has overall responsibility for the TGO Timeline

The ExoMars Trace Gas Orbiter Fig. 6: The CaSSIS flight model on a bench in the University of Bern labo- was launched on 14 March 2016 by ratory. The yellow/red body on the left is the electronics unit. On the right, the telescope structure with the four mirrors is displayed. The telescope is cantilevered a Russian Proton-M rocket from off the gold coloured support structure. (Credit: University of Bern) the Baikonur Cosmodrome in Ka- zakhstan and injected into Mars orbit on 19 October 2016. The subsequent aero-braking phase aims at reducing its speed to a value suitable for the nominal 400 km circular orbit. The science activities start in March 2018 and run for almost two years.

The TGO delivered the Schiaparelli lander on 16 October 2016, which successfully entered the Martian atmosphere returning significant amounts of science data. Unfortu- nately, however, the radio signal was lost during descent and the lander crashed onto the surface.

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173449_Spatium_40_2017_(001_016).indd 10 31.10.17 11:40 The subsequent chapters will provide a brief overview of the CaS- SIS camera which is specifically designed to obtain colour and stereo images. The stereo capability facilitates construction of digital elevation models – effectively providing the topography in addition to the 2-dimensional image.

System Overview

CaSSIS sits on the surface-facing side of the orbiter, see Fig. 5. The orbiter will rotate about an axis that will maintain its solar panels oriented towards the Sun to generate enough electrical energy while avoiding solar illumination of its thermal radiators. This requires CaSSIS to compensate for Fig. 7: The CaSSIS stereo image acquisition principle. During the first part the spacecraft’s yaw rotation with of the orbit (to the left in this sketch), the optical system acquires swaths perpen- dicular to the direction of motion at an angle of 10° to the nadir. Then, the cam- its own mechanism. era is turned by 180° allowing the same region to be observed from a second direction inclined -10° to the nadir. This procedure allows the system to obtain The rotation mechanism is able to quasi-simultaneous stereo pairs over the full swath width for high-resolution dig- turn the entire telescope system by ital terrain models. The resulting images are transferred to the processing comput- ers on Earth, which produce the digital elevation model of the terrain along with 180° in 15 seconds while its sup- the colour images. (Credit: ESA). port structure remains fixed, see Fig. 6. In order to gather the stereo pair of images required for the pro- the spacecraft is in the nominal or- face on the focal plane assembly. It duction of elevation models, the bit (400 km above the surface). was originally conceived as a three- imager looks 10° ahead of the This resolution equals seeing a mirror anastigmatic system (off- spacecraft, as outlined in Fig. 7, to Swiss franc at a distance of 2 km! axis) with a fold mirror. The tight acquire the first image, then it The digital elevation model of the time schedule in the TGO pro- turns by 180° to look 10° back- terrain will have a resolution of gramme required the adaption of wards to acquire the second pic- about six metres in the vertical an existing system for a laser com- ture of the same surface element. direction. munication terminal to satisfy the requirements for CaSSIS. CaSSIS will also deliver high-res- The camera is composed of the fol- olution imagery of the surface that lowing subsystems: The mirror structure is made from allows scientists to investigate carbon fibre reinforced plastic as- whether specific types of geologi- suring excellent stability over the cal processes might be associated The Telescope Unit expected spectrum of thermal and with trace gas sources and sinks. mechanical loads. This subsystem The horizontal resolution is of The telescope unit projects an ac- was designed and fabricated by about five metres per pixel when curate image of the Martian sur- RUAG of Zurich, Switzerland.

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173449_Spatium_40_2017_(001_016).indd 11 31.10.17 11:40 The Focal Plane Assembly

The Focal Plane Assembly converts the incoming light into electrical signals. It is a heritage from the Be- piColombo mission – a slightly adapted flight spare unit from the SIMBIO-SYS experiment. As can be seen in Fig. 9, the detector is covered by a single substrate on which four colour filters are de posited. With these four filters, the detector produces images in four different colour bands which, when composed to one single image, permit the reproduction of natural colours and scientifically relevant colour ratios. To avoid blurring by the speed of the spacecraft, the detector is read-out ex- Fig. 8: The CaSSIS telescope unit. The telescope delivers a precise image of the tremely quickly with 14-bit digi- Martian surface to the focal plane assembly. To reach the challenging thermal and tal resolution. mechanical stability requirements, the unit is made of a carbon fibre reinforced polymer structure. The primary mirror (to the right) is 13.5 cm in diameter. (Credit: University of Bern) The Rotation Mechanism Fig. 9: The focal plane assembly. It serves to convert the incoming light from the telescope into electrical signals. As CaSSIS is intended to provide The rotation mechanism rotates colour images, there are four optical filters directly deposited on a silica substrate that covers the detector unit. The numeric combination of the four data channels the camera’s optical axis, see Fig. 10. delivers imagery in natural colours. (Credit: University of Bern) It connects the telescope unit and the focal plane assembly to the spacecraft. This solves two prob- lems: Firstly, the rotation of the spacecraft about the nadir direction can be compensated for. Prior to image acquisition, the imager can be rotated, so that the lines are or- thogonal to the direction of motion. Secondly, the rotation mechanism can be swivelled by ~180° to acquire stereo images as outlined in Fig. 7.

The rotation mechanism’s gear is made of high-strength titanium al- loys, which are hard-coated to provide durability. A stepper motor, connected to the torus shaft via a

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173449_Spatium_40_2017_(001_016).indd 12 31.10.17 11:40 las Thomas), see Fig. 11 and 12. Most importantly, they confirmed also the instrument’s full functionality.

The upper panel of Fig. 11 is composed of a large number of individ- ual small framelets. Upon pre-processing by the electronics unit, these framelets were transferred to the spacecraft’s telecom system, which in turn sent the data to the Fig. 10: The CaSSIS Rotation Mechanism. The rotation mechanism holds the ESA’s ground station on Earth. telescope unit and the focal plane assembly on the basic instrument structure, which From here, it went to the Univer- in turn is fixed to the spacecraft. It serves to adjust the instrument’s optical axis in the direction needed, for instance to create the stereo images. (Credit: University sity of Bern. With the help of ex- of Bern) perts from the Astronomical Ob- servatory in Padua, the 3D image shown in the lower table of Fig. 11 bellow coupling creates the neces- ments were briefly turned-on to was generated.The colour capabil- sary torque. test the systems. CaSSIS took a first ity of the instrument was also glimpse of the Martian surface and tested and the remarkable picture the imagery returned was abso- of lava flows near Arsia Mons was The Electronics Unit lutely spectacular (original quote returned, see Fig. 12. of the principal investigator Nico- The electronics unit provides the necessary electrical energy to the various consumers in the camera. Fig. 11: Noctis Labyrinthus: a preliminary reconstruction of a detail of the In addition, it performs the first Martian surface. The image in the top panel was gathered by CaSSIS during a first fly-by at Mars before slowing down to the final orbit. The table below dis- step in the digital processing chain plays the reconstructed 3D image from the digital elevation model. (Credit: Uni- of the image data before it is con- versity of Bern) veyed to the spacecraft system bus for transmission to Earth. The electronics unit comprises three modules, which assembled with board-to-board connectors to generate a complete and compact box.

CaSSIS’s First Pictures from Mars

When the TGO arrived at the Red Planet on 22 November 2016, the aero-braking phase began deceler- ating the spacecraft to reach its final 400 km orbit. On the occasion of its first encounter with the planet, the spacecraft and its instru-

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173449_Spatium_40_2017_(001_016).indd 13 31.10.17 11:41 Fig. 12: Lava flow near Arsia Mons. This image is particularly interesting because it does not merely show dark streaks arising from the motion of dust but also a bright region to the upper left which is almost certainly a cloud feature in the lower atmosphere. The detail evident in the image is exquisite. (Credit: University of Bern)

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The Italian astronomer Giovanni In the meantime, scientists explore Schiaparelli15 became world-fa- the Red Planet with the currently mous in 1877 with his maps of the available technology of which the Martian surface, which, however, CaSSIS camera is an excellent ex- the space age debunked as fantas- ample. This wonderful piece of tic interpretations of what his eyes hardware will provide crucial in- may have seen through his (too) formation about the Martian sur- simple lens telescope. Nevertheless, face not least by qualifying land- his publications stirred up the pub- ing sites for future human space lic’s fantasy on a large scale and set missions. the stage for the small green Mar- tians, the possible artificers of the As Carl Sagan16 said, “The cosmos is long water channels Schiaparelli full beyond measure of elegant truths, was thought to have detected. of exquisite interrelationships, of the awesome machinery of nature.” This The technologies have changed is certainly true for Mars in par- since Schiaparelli’s time but the ticular and CaSSIS will help to three ingredients of the story have shed light on that awesome ma- excitingly remained the same: chinery of nature that is at work Mars, water and life. Thanks to an on Mars. armada of spacecraft and rovers exploring the Red Planet in the last five decades, our understanding has grown immensely; and all this tremendous amount of knowledge points towards the possibility of life on Mars either actual or extinct.

This vague option continues prompting space agencies to implement missions to Mars. Within perhaps two decades, this planet may even come into the reach of human space flight, which then will give rise to a new chapter of the Mars exploration story.

15 Giovanni Virginio Schiaparelli, 1835, Cuneo, Italy – 1910, Milan, Italian astronomer. 16 Carl Edward Sagan, 1934, Brooklyn, New York – 1996, Seattle, Washington, American astronomer, cosmologist, and science communicator.

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The Author

Tucson, and at the Queen’s Uni- versity of Belfast. In March 2003, the University of Bern elected him as Professor of Experimental Physics.

Nicolas Thomas is the Principle Investigator for the Microscope on the Beagle 2 Lander and the Co- Principle Investigator of ESA’s BepiColombo Laser Altimeter Experiment to Mercury. In addition, Nicolas Thomas has held leading responsibilities with numerous other science instruments and served in various international space science teams. Specifically, he was a Member of the Scientific Board of the International Space Sciences Institute 2003–2006 and Nicolas Thomas gave his first phys- continue his studies at the Univer- later a Member of the ISSI Board ics lecture at the tender age of eight. sity of York with a thesis about Io’s of Trustees (2011-present). Like his colleagues, he was asked atmosphere, which earned him the to present a topic of interest; and as Stott prize for the best physics thesis Over the years, Nicolas Thomas at that time, Neil Armstrong had at the University of York in 1986. has published over 100 publications just set foot on the lunar surface, covering the fields of cometary, young Nicolas decided to give a His career then led to the Max Jupiter and Mars research. He is presentation on the solar system. Planck Institute for Aeronomy deeply fascinated by the beauties This laudable attempt, however, (MPAe) of Lindau, where he and miracles of our solar system, was stopped at Jupiter since his time worked on the analysis of data even, as he underlines, as a non- allowance of two minutes was over from the Halley Multicolour believer that there is life elsewhere at the giant planet. Notwithstand- Camera aboard the Giotto space- in our solar system. But further out ing this setback, planetary science craft. A further post-doctoral there? That is another story … continued to fascinate the young- fellowship allowed him to join Scientists should maintain skepti- ster who took up where he left off the Space Science Department of cism, he confesses, and base argu- by writing a review about the Jo- ESA, and then he returned to ments on facts. One does not have vian satellite, Io, when completing MPAe. During that time, he was to “spice up” the stories in our so- a Master’s degree in Experimental also engaged as a visiting scientist lar system to fascinate the public. Space Physics at the University of at the Lunar and Planetary Labo- Just tell them the truth. That is Leicester. This encouraged him to ratory at the University of Arizona, beautiful enough.

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