Mars Exploration BY DR. GIANCARLO GENTA

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2 On the History and Future of Mars Exploration BY DR. GIANCARLO GENTA 2 The Planet For centuries Mars, the Red Planet, has wielded considerable influence over the imaginations of mankind across all cultures. In mythology, probably owing to its deep, blood red-color, it was associated with the god of war. Not the god dealing with the rational, strategic kind of war that was the concern of Athena but with vengeful, violent, and irrational war. Both astrology and, as it became a science, astronomy have dealt with the Red Planet. In the second half of the 19th century three great astronomers, the Italian Giovanni Schiaparelli, the French Camille Flammarion, and the American Percival Lowell, contributed much to the scientific knowledge of Mars and to its myth. The former drew a number of maps, which remained the best maps of Mars until the Peter Paul Rubens Mars and Rhea Silvia. first pictures of the planet were taken by space probes. Nineteenth-century astronomers observed intriguing features on the Martian surface: straight, dark lines. Schiapparelli described them using the Italian term canali, which designates both artificial and natural waterways. This was translated into English as canals, originating the myths about the Martian civilization that built these massive works of engineering. While Schiapparelli restricted his scientific papers to detailed descriptions of what he observed, it wasn t for lack of his speculations regarding the planet s inhabitants. In a number of Percival Lowell sowed seeds of both fact and Giovanni Schiaparelli, Camille Flammarion, and fancy.

3 popular science articles, he set his imagination free, proposing that the dark lines were in fact areas dense with vegetation that flanked artificial waterways, presumably built by an ancient civilization in an attempt to survive the desertification of the planet by bringing water from the melting polar caps to the more temperate and equatorial zones. Consequently, the idea that intelligent beings lived on Mars came to be generally accepted; many novels, from The War of the Worlds by H.G. Wells to Under the Moons of Mars by E.R. Burroughs, from The Martian Chronicles by R. Bradbury to The (in-)famous Martian canals/channels, according to Out of the Silent Planet by C.S. Schiaparelli, from Flammarion (1892): La Planéte Mars. Lewis, were based on this idea. Even if in the first half of the 20th century some of the classic misunderstandings on Mars were clarified there was neither oxygen nor water vapor in Mars atmosphere, very little liquid water, if any, could exist on the surface, the channels were an optical illusion (artifacts of the low-resolution telescopes), and so forth the general picture outlined by Schiapparelli and Lowell persisted. In the general understanding of the time, Mars was a barren world with a very thin atmosphere, but it was nonetheless habitable, at least by primitive forms of life. If intelligent beings were living there, they would have had to seek refuge underground, perhaps aided by those fanciful atmospheric machines that were depicted in the many fictional descriptions of the time. When the idea of crossing the gulf of space shifted from fantasy to serious scientific study, human missions to Mars were proposed. Yet even then, traces of the fantastic imaginings of the 19th-century astronomers remained. In 1960, only three years after the launch of Sputnik 1, the Russians launched the first two probes to Mars. Both failed, however, as did the three subsequent attempts launched in 1962 and another in In 1964, the Americans tried their hand at a Martian probe, launching Mariner 3 and Mariner 4, also intended to do flybys of the planet. The first failed, but 3

4 Mars 1M No.1, designated Mars 1960A by NASA analysts and dubbed Marsnik 1 by the Western media, was the first spacecraft launched as part of the Soviet Union s Mars program. A Mars 1M spacecraft, it was intended to conduct a flyby of Mars; however, it was lost in a launch failure before it could begin its mission. Image courtesy of NASA. Mariner 4 reached Mars on January 14, 1965, and sent back 22 photos. Even if they depicted only 1% of the surface of the planet, these images forever changed mankind s conceptions of the Red Planet. It turned out that the surface of Mars was very similar to that of the moon: covered with craters and utterly dry. Not only were there no canals, there were no warlords or Martian princesses to be detected anywhere beneath the moons of Mars. No vegetation, no rivers, no lakes. Some of the craters seemed to have some traces of ice, but nothing else. The instruments also revealed that Mars had no magnetic field, meaning there was nothing standing between its surface and the bombardment of cosmic radiation. In addition, the atmosphere, composed of carbon dioxide, had a much lower pressure than previously thought. Not only could you not breathe the Martian air, just going Mariner 4 was launched and traveled toward Mars. As the first deep space satellite to utilize the higher S-band frequency (2 to 4 GHz), it had more powerful uplink capabilities than previous missions. Mariner 4 was also the first satellite to take the first up-close pictures of another planet. Mariner 4 ceased transmitting in Image courtesy of NASA. 4

5 outdoors would require a full spacesuit, just as in interplanetary space. The Mariner 6 and Mariner 7 probes, launched in 1968, substantially confirmed these conditions. In addition, the southern polar cap proved to be made more of dry ice (frozen carbon dioxide) than water ice. In 1971, Mariner 9 was launched with a much more ambitious plan: become the first spacecraft to orbit another This Mariner 4 image is the first close-up phoplanet rather than simply perform a flytograph ever taken of Mars. This shows an area by. When it arrived, it was greeted by about 330 km across by 1,200 km from limb to bottom of frame, centered at 37 N, 187 W. The area a sandstorm of global proportions an is near the boundary of Elysium Planitia to the unexpected situation that also explained west and Arcadia Planitia to the east. The hazy Mars occasional changes in color. area barely visible above the limb on the left side of the image may be clouds. Image courtesy of NASA. When the dust storm settled down after several months, images began arriving by the thousands. And with the photographs came more surprises: Mars was actually much more complex than originally thought. It was certainly not the planet of Schiapparelli s and Lowell s imaginations, but neither was it a dead world like the moon. There were massive volcanoes and many canyons, the largest of which was named Valles Marineris in honor of the probe that had discovered it; it was a canyon that might This view of channels on Mars came from contain several times the volume of wanasa s Mariner 9 orbiter. In 1971, Mariner 9 became the first spacecraft to enter orbit ter of the Colorado River. Moreover, the around Mars. Credit: NASA/JPL-Caltech. pictures clearly showed the dry beds of huge rivers and lakes, perhaps even seas. While Mars might be dead now, long ago there was indeed water and, perhaps, life. And, if there was life, perhaps in some protected places it might have survived to the present. 5

6 The promising results obtained by the Mariner probes propelled further Mars exploration. In 1975, a pair of probes, Viking 1 and Viking 2, each comprising an orbiter and a lander, were launched by NASA. Both landers managed to get to the ground, landing in sites respectively called Chryse Planitia and Utopia Planitia, the names given in Schiapparelli s maps. In addition to taking a large number of pictures and collecting data, the two landers performed three experiments: they gathered soil samples and analyzed them for signs of biological life. The results were unexpected and somewhat enigmatic but did not show the presence of lifeforms, even microscopic ones. Apparently the Martian soil is completely sterile, owing to the combination of ultraviolet radiation from the sun, extreme dryness, and the presence of oxidizing compounds. The probes revealed the disappointing truth that Mars was very different On August 20, 1975, Viking 1 was launched by a Titan/Centaur rocket to begin a half-billion mile, 11-month journey through space to from what was believed or hoped for explore Mars. The four-ton spacecraft went more than a century. By the end of the into orbit around the Red Planet in mid- 1970s many doubts were expressed, Image courtesy of NASA. not only about the possibility of discovering lifeforms, but even about the possibility of exploring and colonizing the planet, stalling further exploration for almost two decades. Fortunately, subsequent studies performed by other robotic probes rekindled interest in human exploration. As a result, today we know that on Mars there are large quantities of underground water, even if not in the liquid state. Oxygen and hydrogen can be obtained from this water and, with the help of hydrogen split from it, oxygen and methane from the atmosphere. The soil can be used for cultivating plants, opening up the possibility of future colonization of the planet. Enlightened though we may be, however, the charm of the early astronomers Mars is forever lost. 6

7 Exploring Mars The early ideas about how to get to Mars and survive there can be found in the works of the pioneers of space exploration, including Tsiolkovsky, Goddard, Oberth, and many others. However, these visionaries failed to provide the details needed to actually design a viable mission to Mars not only the requisite technical details, but studies concerning the feasibility, economic sustainability, and the risks associated with sending astronauts to Mars and bringing them back. These early projects were based on the descriptions of Mars by Schiapparelli and Lowell: a barren, but not completely dead, world, with an unbreathable atmosphere but one in which a space suit would not be required. Moreover, in spite of its low density, they assumed an atmosphere that could easily sustain flying machines. Hostile, yes, but not completely uninhabitable. Moreover, it was assumed in these early plans that the astronauts would arrive on Mars without the benefit of all the information about the planet that we now take for granted. Consequently, they would spend the first days in orbit around the planet in order to study the planetary surface and to decide where and how to land. Without the aid of sufficiently autonomous robots to act as advance scouts, they would discover what was on the planet friendly or otherwise only upon landing. The first proposal was conceived and developed by none other than Wernher von Braun. Written between 1945 and 1948, it was ultimately published in 1949 with the German title Das Marsprojekt. It provided a very detailed specification, which demonstrated unequivocally that it was indeed possible to reach Mars with a technology predicted for a not too distant future. An English translation was published in 1952 [1]. In von Braun s scheme, a fleet of ten 3,720-ton spaceships, with a total crew of 70 astronauts propelled by chemical rockets with nitric acid and hydrazine would be built in Earth orbit by launching from Earth 950 multistage rock- 7

8 ets (about twice the size of present launchers but less than half that of the Saturn V) used to carry humans to the moon. Today we know that the project was feasible from a technical point of view, but it was economically unsustainable. Von Braun also wrote a science fiction novel, likely originated in the early 1950s but only published in 2006 [2], based on his proposal. The novel is actually quite realistic, except for the description of the planet, which was consistent with Schiapparelli s and even with E.R. Burroughs Mars. Notwithstanding, von Braun s preface makes clear the serious nature of the subject matter: With the utmost care I have avoided delving into the realms of fantasy in describing physical conditions or phenomena encountered on the trip to Mars, nor have any assumptions based solely upon vague theories been used. No miracle chest from which the presiding genius produces at will death rays or cosmic energy will be found aboard my space ships. This is in contrast to so many science fiction stories which rely for their plausibility upon mysterious knowledge springing from the brains of some intellectual superman. My ships are propelled by compounds well known to the chemical fraternity. They are constructed of familiar materials. Even their equipment is built up around presently familiar methods and procedures. In other words, they are but a projection, an extrapolation, a natural development of a still youthful but solidly established technology. Contemporary with these ideas, the Russians had been expressing their interest in Mars exploration by advancing some projects of their own. Beginning with their work in the late 1960s, the Russian projects for Mars were based on the N1 rocket, which had originally been developed to reach the moon. However, the multiple failures of the N1 program led to their abandoning most of these plans. Also in the 1950s, great hopes were laid upon nuclear energy, as it was realized that Soviet N1 rocket. 8

9 only nuclear spaceships would enable safe and reliable travel through the solar system. The simplest solution employed a nuclear reactor to produce electrical energy to power ion or plasma thrusters. Moreover, in the 60s and 70s both the Americans and the Russians had launched nuclear reactors into orbit to power satellites. The problem was just building more powerful and lightweight reactors. In 1962, when President Kennedy declared the American commitment to a human mission to the moon, he also stressed the importance of developing nuclear propulsion specifically a nuclear thermal thruster whose energy would be used to heat the liquid hydrogen propellant and also provide Concept art of one of the Nuclear Electric Propulsion (NEP) spaceships of the Stuhlinger project approaching Mars. Ernst Stuhlinger was a German-born American atomic, electrical power for operations electrical, and rocket scientist brought to the United States and scientific instrumentation. as part of Operation Paperclip. He developed guidance The nuclear thruster was, systems with Wernher von Braun and later was a scientist with NASA, where he was instrumental in the development in fact, built and repeatedly of the ion engine for long-endurance space flight. bench-tested with excellent results [3], but further development stalled. In Russia, studies on nuclear thermal propulsion continued until they were curtailed by the economic crisis brought on by the fall of the Soviet Union. The United States subsequently discontinued its work in nuclear thrusters in In any event, even if it is possible to reach Mars using chemical propulsion, nuclear propulsion whether thermal or electric (where nuclear thermal energy is converted into electrical energy) is today the only practical means for reliable and consistent human missions to Mars. And both approaches, thanks to the tests of the 1970s, have been shown to be both technically and economically feasible. 9

10 The arguments about propulsion systems, though, are far from settled. For a discussion of these issues, and also about the possibility of life on the Red Planet, see [4 12]. The Journey The simplest mission to Mars is a flyby, like the one recently proposed by the nonprofit organization Inspiration Mars Foundation [13]: a cruise around Mars in about 500 days for two people. The mission, scheduled Artist s concept of Inspiration Mars flyby. for 2018 (or 2021, if the first deadline is Credit: Inspiration Mars Foundation. missed), is based on a commercial capsule attached to an inflatable module to increase the space available to the astronauts on board. However, it seems unlikely that two people can live for more than a year in such a small space, and other technical aspects seem at least problematic. Above all, in a flyby the spacecraft remains close to the planet for just a few hours, and little scientific work can be performed. Slightly more complex than a flyby is a mission to orbit Mars or to land on one of its satellites. The energy required is slightly greater than that for a flyby, but the astronauts can stay close to the planet longer in order to study it. Moreover, the astronauts can teleoperate probes from orbit and obtain detailed information about the planet. The greatest problem of robotic Mars exploration is linked with the time required for any command sent from Earth to reach the robot and for the operator to know how the probe responded to the command. Under these conditions teleoperation from Earth is quite difficult, and so the devices must be as autonomous as possible. If the operators of the probes are in orbit around Mars, everything becomes much easier. (To learn more about teleoperation, see Mechanix Illustrated, Fall 2017.) The time to spend in orbit or on a satellite of Mars, or the time spent on the surface in the case of landing, cannot be chosen arbitrarily: the dates of the outward and return journeys must be established according to the motion of the two planets. A date about days before opposition must be chosen to depart from Earth, but this date also depends on the particular launch 10

11 opportunity and the trajectory chosen. The cheapest journey takes about 260 days and, if a similarly economic trajectory is chosen for the return trip, the crew must wait on Mars, or remain in orbit, about 450 to 500 days before returning a longstay mission of about 1,000 days in total. If you wanted to come back earlier, you could not stay on the planet or in orbit for more than 30 or 40 days. Moreover, the return journey requires more energy and is slower. It may also be necessary to perform a flyby of Venus in a gravitational slingshot to speed the craft s onward journey to Earth. Missions of this type are shortstay missions of around 550 days. The total mission time is shorter, but many more days are spent in space, leaving less time for exploring the planet. In a 501-day flight to Mars, the spacecraft first falls inward Recently, one-way missions toward the sun to be accelerated by the gravity. Then the have been proposed. While it is craft is hurled outward, passing Earth s orbit to intercept true that colonization voyages are Mars near the height of its trajectory. Figure not to scale. one-way trips, it is equally true that, to ensure that the settlers can survive indefinitely on Mars, life support systems far more advanced than current ones must be developed. In practice, while indefinite-stay missions can greatly simplify the journey, they will complicate other aspects of the mission. The Dutch non-profit organization Mars One [14] is planning a number of oneway trips to Mars with the goal of colonizing the planet. The first trip should take place in 2026, with the selection of the astronauts already underway. However, a recent MIT study [15] showed that the environmental control and survival systems planned for the mission are not adequate, and the astronauts could survive only a few months. While humans will someday live on Mars indefinitely, it is doubtful that this will be accomplished with the first mission. 11

12 The Outpost Life on Mars will not be easy. The first astronauts will have to take with them all that they will need, except for the few things they ll be able to obtain onsite. In any case, to exploit the local resources, they will need a number of devices that must also be carried from Earth. If water, oxygen, the fuel for the return journey, and all the other consumables are carried from Earth, only a limited amount of electrical energy will be needed, and solar panels would suffice. But the equipment needed to establish a sustainable living environment comprises supplies amounting to tens of tons. Consequently, a much larger electric power source and a nuclear reactor will be required. Moreover, the use of solar panels on Mars is also made difficult by the distance of the planet from the sun, the constant need for cleaning (panels quickly become covered in Martian dust), and the need to store energy: solar panels do not produce energy when it is needed most, and the temperature drops to less than 100 C below zero during Martian nights. On their way to perform surface experiments, two residents of the first Martian outpost pause to look at their home. Extensive use of natural Martian resources for propulsion would greatly reduce the cost of establishing such a base, and, in addition to continued use for propulsion, material processing plants would provide products that would minimize reliance on the Earth-to-Mars supply line. Image courtesy of NASA. 12

13 New technologies are, however, radically changing things. 3D printing makes it possible to manufacture spare parts onsite, increasing safety without having to carry from Earth a huge amount of spare parts, but they do require a complete redesign of all onboard systems. The same applies for the habitats. Recent studies in 3D printing of housing conducted by China, Italy, and other countries show the possibility of constructing habitats on Mars using locally sourced materials. Not only would a mission not have to carry building materials from Earth, but such technology could be used to build functional homes, roomy and comfortable and that, above all, provide protection from cosmic radiation. In addition to a power plant, Mars habitat built by 3D printing. Third-place finalist from a facility for the production of Team LavaHive in NASA s 3-D Printed Habitat Challenge Design consumables, and the habitat, the outpost must also be Competition. Image courtesy of NASA. supplied with scientific equipment, vehicles for exploration (one or more small vehicles the size of a quad, and a vehicle with a pressurized cabin for longrange excursions), various devices such as robotic rovers, drillers, and so on. Finally there is the problem of environmental contamination, both the socalled forward contamination, i.e., of the planet by humans, and the backward contamination, i.e., of the crew and the terrestrial environment by the planet. Precautions against such contamination must be designed into the first mission. If evidence is sufficient to show that Mars is, in fact, a lifeless planet, environmental rules might then be relaxed. Initially, the planet s surface would likely be divided into two zones: a zone of little biological interest, which may be explored directly by humans, and so-called special zones, areas of great biological importance, with access only by autonomous or remotely controlled rovers. The former, because it is almost certain that the Martian surface has been sterilized by solar ultraviolet radiation, cosmic radiation, and highly oxidant dust, which would have decom- 13

14 posed any organic substance, would be available for direct human exploration. Sheltered places, like caves and other underground locations (several of which have already been discovered), canyon bottoms, and so forth, would be considered special zones. The Landing Site Mars is a small planet, but it is a big place to explore. Its total surface area is roughly that of the combined continents of Earth, and it likewise exhibits a wide variety of geological features. Its exploration is, therefore, a massive task one so large that a single exploratory mission would merely scratch the surface. Rather, what is called for is a sustained campaign comprising a series of well-coordinated missions that build upon one another. Not only would the results and learnings accumulate across missions, such an approach would be far more cost-effective than separate and independent missions. If the primary goal of exploration is the scientific study of the planet from geological and bioastronomic points of view, the most practical strategy would be to land each mission of the campaign in a different place, as was done in the Simplified map of the Martian surface (from a NASA image). The approximated landing sites of the probes are: successful landings - indicated with (+) - 1: Viking 1 (July 20, 1976); 2: Viking 2 (September 3, 1976); 3: Mars Pathfinder - Sojourner (July 4, 1997); 4: Spirit (January 3, 2004); 5: Opportunity (January 24, 2004); 6: Phoenix (May 25, 2008); 7: Mars Science Laboratory - Curiosity (August 6, 2012). Crash landings - indicated with (*) - 1: Mars 2 (November 27, 1971); 2: Mars 3 (December 2, 1971); 3: Mars 6 (March 12, 1974); 4: Mars Polar Lander (December 3, 1999). 14

15 Apollo missions to the moon, beginning with the more accessible sites and progressing to the more challenging locations in subsequent missions. If, on the other hand, the main goal of the exploration campaign is to learn how to live on NASA s Sojourner robotic rover examining a boulder on Mars the planet with an ultimate goal Chryse Planitia, as imaged by its parent spacecraft, Pathfinder, after landing on the planet on July 4, of colonization, all missions Image courtesy of NASA. should land in the same place where buildings, vehicles, and hardware could accumulate, culminating in a permanent base. Operations constrained within this single zone would also have the benefit of minimizing environmental impact and protecting potential indigenous lifeforms, while explorations beyond the inhabited zone would be accomplished with the help of teleoperated equipment, which would be far less likely to introduce contaminants. The selection of such a concentrated site should also seek to minimize hardships for the inhabitants. For example, it is easier to land in a low-altitude location where the dosages of absorbed radiation would be lower. A flat plain with few obstacles and little sand would provide a better situation for landing and traveling on the surface. A site close to the equator would ease launching the return spacecraft, but a latitude of at least 30 or 35 would be preferred for the possibility of finding underground ice close to the surface, or perhaps even liquid underground water, which might be found at less depth. Another point is the distance from The southern rim of Argyre Planitia places of scientific interest in particular those of astrobiological interest. crater on Mars. Image courtesy of NASA. Not 15

16 too close, to avoid contamination, but also not too far away, in order to make them accessible to teleoperated rovers or drones. If long-term colonization plans, or perhaps even terraforming plans, are developed, landing should occur in a place which could, over time, develop into a city. As such, it should be far from zones having a deep permafrost layer, which, in the terraforming operations, may be subject to landslides or other geological instabilities. Places that might be subject to flooding should also be avoided. Who knows what effects the terraforming operations might produce?! The Argyre Planitia region or the deepest, southernmost parts of Hellas Planitia, for example, would be good choices thanks to low levels of radiation and potentially greater water availability, but they are far from places of interest, and in the event of terraforming, they d be the first to become submerged. Another good choice might be the northern plains, like those of Utopia or Cryse Planitia. They have low altitude, flat ground and a likely presence of underground ice, and they are fairly well known. The plains north to the Acheron Mountains may be an even better choice, because they are not too far from the lava tubes of Alba Patera and the Tharsis Bulge volcanoes. If there will ever be a terraformed Mars, the zone north of the Tharsis Bulge may became an important region. Yet another alternative could be the Elysium plains, but this area is farther away from places of bioastromic interest. Volcanic cone in the Nili Patera caldera on Mars, showing hydrothermal mineral deposits (the light-toned patches on the closest flank of the cone). Such deposits are evidence for a past environment that was warm and wet, possibly hospitable to microbial life. Credit: NASA/JPL-Caltech/MSSS/JHU-APL/Brown Univ. 16

17 Life on Mars Evidence of life on Mars, current or fossil, is a subject stirring scientific interest and general debate (see, e.g., [16, 17]). Present conditions on the Martian surface are quite unfavorable to life, at least in terms of life as we know it on Earth. The absence of a magnetic field and the very thin atmosphere allow radiation from space, including galactic cosmic rays (GCR) and radiation from the sun, to reach the surface, and the low temperatures and atmospheric pressure preclude liquid water from forming at the surface. Moreover, the regolith covering the surface of the planet contains chemical compounds that decompose practically all organic matter. Not only has no living organism yet been found, neither have any native organic substances been discovered. (Organic matter has been detected in meteorites and comets, and even in the interstellar clouds.) Mars surface seems to have been sterilized by a number of agents, both radiological and chemical. Yet we cannot conclude that Mars does not host underground life. Even Earth, while being so conducive to life on its surface, still hosts myriad underground lifeforms. That said, completely different forms of life may actually thrive in Mars environment, even on its surface. To survive in such an environment, though, these lifeforms must be based on a quite different chemistry, and we do not know whether life is a phenomenon necessarily NASA s Hubble Space Telescope s Wide Field and Planetary Camera 2 snapped these linked to carbon chemistry (what we know images showing the north polar cap tilted as organic chemistry) or not. toward Earth. The image was taken in the One of the basic assumptions, which middle of the Martian northern summer, guides many searches for extraterrestrial when the polar cap had shrunk to its smallest size. During this season the sun shines life, is that life needs water as a solvent. continuously on the polar cap. Previous This assumption may be too provincial telescopic and spacecraft observations have or Earth-centric, but it may well be necessary at this point in our current state of shown that this summertime residual polar cap is composed of water ice, just like Earth s polar caps. Image courtesy of NASA. scientific knowledge: either we search for 17

18 water-based life, or we simply don t know what to look for. Consequently, most searches for Martian life are based on the follow the water model. And by this we mean liquid water, not ice, which we know is present in many places on Mars, from the polar caps (mainly the northern cap, but also the southern) to the underground permafrost, which is sometimes very close to the surface. Finding water ice is very important for Mars colonization, but it is useless in the search for life. But we are also sure that liquid water existed in the (very remote?) past on the surface of Mars, which would have been conducive, at least in part, to some form of Martian life. For this to be true, certain conditions, about which we know very little, would likely have been present. For example; The surface was in some way screened from radiation from space. There are clues that at one time Mars had a global magnetic field, which may have acted as a magnetosphere. If so, then the Martian atmosphere would likely have been much denser than it is today, perhaps up to twice as dense as Earth s present atmosphere. This may also have caused a larger greenhouse effect leading to much warmer conditions, even if others think that ancient Mars was colder than present Mars due to the lower energy emitted by the sun. In any event, the higher atmospheric pressure would have allowed the presence of liquid water on the surface. The surface was chemically more life-friendly. This may well have been possible, since the present oxidant compounds (mainly peroxides) could have been the result of billions of years of exposure to ultraviolet radiation. Finally and this is the main point we are not at all sure that life is a sort of nature s must. If on Mars the conditions were not so unfavorable to life as they are today, does that necessarily mean that life did, in fact, exist? At present we are unable to answer this question. If life ever existed on Mars, then we should at least find fossils, but it is likely that we will have to look for them underground or at least in protected places. Summarizing, we must consider four alternatives, which are consistent with what we know of the planet: 1 Life never existed on Mars. 2 Life started, but then disappeared from the planet, leaving only fossils for us to discover. 3 Life started, then disappeared from the surface, but remains in a few un- 18

19 derground places. Fossils may be found, but it may be quite difficult to find the few surviving forms of life and to distinguish this alternative from the former one. 4 Life started, then disappeared from the surface to remain a widespread occurrence in the underground. In this case, it may be relatively easy to find it. In the last two cases it is possible that any microbes would likely be dormant down to a depth of a few meters beneath the surface, cryopreserved by the current freezing conditions, and so metabolically inactive. They would be unable to repair cellular degradation as it occurs. If this is true, to search for active organisms we should investigate fairly deep subterranean places, where past volcanism may have created subsurface cracks and caves within different strata, and where liquid water could have been captured, forming large aquifers, with deposits of saline liquid water, minerals, organic molecules, and geothermal heat. This habitable environment, away from the harsh surface, may be where life still survives. Some speculate that the small quantities of methane and formaldehyde detected by Mars orbiters are potential evidence for this subterranean life, as these chemical compounds would quickly break down in the Martian atmosphere. However, they may instead be produced by volcanic or other geological processes. Living on Mars The duration of the solar day on Mars, usually referred to as a sol, is quite close to the duration of a day on Earth, so that astronauts, followed by colonists, will be able to adapt themselves easily to the Martian day. The first and more common way of recording time on Mars is subdividing the sol, which has a duration of 24 hours, 39 minutes, 35.2 seconds, into 24 Martian hours, each one comprising 61.6 minutes. The second possibility, followed in the science fiction novels by Kim Stanley Robinson [18], is keeping 24 Earth hours and then adding a 39-minute, 35-second period in which all activities are suspended. In the novels this peculiarity becomes a characteristic feature of the new Martian way of life. While the Earth year is subdivided into 12 months, which are reminiscent of the lunar calendars preceding the solar calendars, on Mars there is no slowly 19

20 moving moon to provide a simple reference for subdividing the year, which is much longer than Earth s year. The Mars tropical year is about 687 days or 669 sols. Owing to the fact that the inclination of the planet s rotation axis is similar to that of Earth s (25.19 versus ), the seasons are similar to those of Earth, although the Martian seasons interact with the much higher eccentricity of its orbit. A hypothetical map of a fully terraformed Mars [20]. The fact that the planet is closer to the sun at the northern winter solstice makes the seasons more extreme in the southern hemisphere, which has short and hot (for what hot might mean on a cold planet like Mars) summers and long, cold winters. The Future There is no question that Mars figures in the future of humankind: the more technology advances, the more it becomes cheaper and safer to get there. Moreover, despite periodic economic crises, the size of the world economy continues to grow, and thus the resources available to go to Mars perhaps those of private companies that are free from the constraints, inertia, and inability to pursue an end without shifting goals typical of public organizations increase. The problem is not so much whether we will go to Mars, but when. And then? If we find life on Mars, it will constitute the first studies, and Mars exploration will initially be a scientific enterprise. We will build a scientific station, perhaps similar to those in Antarctica, and from there rovers will explore the most interesting places. If, on the other hand, Mars proves to be a lifeless planet, we can begin to import terrestrial forms of life and, with time, we will start thinking of terraforming its surface [17, 19], making it suitable to sustaining human life, and initiating a kind of planetary restoration operation. We may, in fact, bring about the planet dreamed of by Schiaparelli and Lowell, where Mars may again have an atmosphere worthy of the name, as well as rivers, lakes, and seas. And perhaps even canals. 20

21 Acknowledgements The author coordinated the study group of the International Academy of Astronautics (IAA), whose aim is to study a global human Mars Mission (SG 3.16) and is now coordinating its follow-up (SG 3.27). While deeply indebted to all the members of the study groups, the author stresses that the ideas expressed here are his own and do not involve either the study groups or the IAA. References [1] W. von Braun, The Mars Project, University of Illinois Press, 1952 (2 Ed., 1991). [2] W. Von Braun, Project Mars: A Technical Tale, [3] J. Dewar, The Nuclear Rocket, Apogee Books, Burlington, Canada, [4] Human Exploration of Mars: The Reference Mission of the NASA Mars Exploration Study Team, NASA SP NASA Johnson Space Center, [5] R. Zubrin, D. A. Baker, Mars Direct: A Proposal for the Rapid Exploration and Colonization of the Red Planet, in S. Schmidt, R. Zubrin, Islands in the Sky, Wiley, New York, [6] B.G. Drake ed., Reference Mission Version 3.0 Addendum to the Human Exploration of Mars, EX ADD, NASA Johnson Space Center, [7] L. Bergreen, The Quest for Mars, Harper Collins, London, [8] P. Clancy, A. Brack, and G. Horneck, Looking for Life, Searching the Solar System, Cambridge Univ. Press, Cambridge [9] D. Rapp, Human Missions to Mars, Springer-Praxis, Chicester, [10] B.G. Drake ed., Mars Architecture Steering Group, Human Exploration of Mars, Design Reference Architecture 5.0 (and addendums), NASA Johnson Space Center, [11] IAA Study Group 3.16 Global Human Mars System Missions Exploration Goals, Requirements and Technologies, IAA, [12] G. Genta, Next Stop Mars: the Why, How and When of Human Missions, Springer, New York, [13] [14] [15] S. Do, A. Owens, K. Ho, S. Schreiner, O. de Weck, An independent assessment of the technical feasibility of the Mars One mission plan Updated analysis, Acta Astronautica 120 (2016) [16] G. Genta, Lonely Minds in the Universe, Springer, New York, [17] B. Jakowsky, The Search for Life on Other Planets, Cambridge University Press, Cambridge, [18] K. S. Robinson, Red Mars, Green Mars, and Blue Mars, Bantam Books, New York, 1993, 1994,

22 [19] R. Zubrin, C.P. McKay, Terraforming Mars, in S. Schmidt, R. Zubrin, Islands in the Sky, Wiley, New York, [20] About the Author Giancarlo Genta received a degree in aeronautical engineering in 1971 and in aerospace engineering in 1972 at the Politecnico di Torino, where he became assistant professor of machine design. He taught a course in astronautical propulsion and lectured in motor vehicle mechanics. In 1983 he became associate professor of design of aircraft engines at the School of Aerospace Engineering of Politecnico di Torino, later becoming full professor in machine design. From 1989 to 1995 he was head of the Department of Mechanics at Politecnico di Torino. From 1998 to 2015 he coordinated the Ph.D. course in mechatronics at the Ph.D. School of Politecnico di Torino. He gave courses in Italy and abroad in the context of different programs for developing countries in Kenya, Somalia, and India, and at the International Labour Office. Dr. Genta is responsible for the courses in automotive engineering of Politecnico di Torino. Since 1999 he is a member of the Academy of Sciences of Torino, and since 2006 he is a member (corresponding member since 2001) of the International Academy of Astronautics. In 2013 he received the International Yangel Medal for Outstanding Contributions to the development of space sciences and technologies and, in the same year, received the Engineering Science Award for outstanding achievement in engineering science of the International Academy of Astronautics. He performed research, mainly in the field of machine design, in particular dealing with static and dynamic structural analysis. He worked in the field of magnetic suspension systems and in general of the dynamics of controlled systems. He was one of the promoters of the Interdepartmental Laboratory of Mechatronics, which works in the areas of magnetic bearings (active, passive, and superconducting) and mobile robots. Since 1996 he deals with space systems and space robotics. Since 2012 he heads the IAA Study Group on Human Mars Exploration (SG 3.16, and then SG 3.27). He is a member of the Advisory Board of the Starshot Project. He participated in the design and construction of experimental equipment that is currently part of the Laboratory of the Mechanical and Aerospace Engineering Department of the Politecnico di Torino. He is the author of over 350 scientific papers covering various sectors of mechanical design, published in scientific journals or presented at conferences, and of four patents. He is the author of 24 books, including textbooks, research monographies, and popular science books. He is also the author of two science fiction novels, published in Italian and English. For more information and for details about the books, see 22

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