INTERNATIONAL SPACE SCIENCE INSTITUTE SPATIUM Published by the Association Pro ISSI No. 24, February 2010 Editorial

One might consider space science Space science helps us to under­ unrelated with our human history. stand the miracle of our existence. Impressum This may be one of the reasons why You, dear reader of Spatium, know space science is at the core of the that nothing could be more wrong. European Space Agency ESA (of Without taking into consideration which Switzerland is a founding the cosmic past, our presence here on member) and this is also why our SPATIUM Earth appears to be a mere matter of Pro ISSI association invited Pro­ Published by the course. lt is on the stage of space fessor David Southwood, Director Association Pro ISSI science that our life reveals itself as of ESA’s Science Programme, to the result of events commencing present the current status of the right in the universe’s earliest mo­ programme together with his ments. Take, for example, water, our visions for the years to come. The body’s major constituent: it consists Cosmic Vision, ESA’s master plan Association Pro ISSI of two hydrogen atoms united with for space science, is federating the Hallerstrasse 6, CH­3012 Bern one oxygen atom. While the first European skills together with those Phone +41 (0)31 631 48 96 come unaltered from the unimagin­ of other space­faring nations to see able events in the Big Bang, some address jointly the most fascinating www.issibern.ch/pro­issi.html 14 billion years ago, the latter is the topics in space research. for the whole Spatium series result of nuclear fusion processes in stars that shined and died long before The present issue of Spatium sum­ President our solar system saw the light of the marizes Prof. Southwood’s talk as Prof. Klaus Pretzl day. No doubt: our roots are deeply well as the Agency’s Cosmic Vision University of Bern anchored in the cosmos’ distant past. plan. We are indebted to Prof. Rudolf von Steiger, Director at Layout and Publisher Not only, though. Take for instance ISSI, who cared about the scientific Dr. Hansjörg Schlaepfer the Sun: for 4.6 billion years our correctness of the present text. CH­6614 Brissago daytime star has delivered the warmth enabling life to evolve on The present issue of Spatium is also Printing Earth. Still, like every medal, the a summary of its forerunners; with Stämpfli Publikationen AG Sun has two facets as well: it emits the Cosmic Vision in mind, it sets CH­3001 Bern not only the visual light, to which the stage for all the fascinating re­ our eyes are so well adapted, but also sults to be reported in future issues ultraviolet radiation that is harmful of Spatium. to living cells. This dangerous part of the Sun’s radiation creates the Brissago, February 2010 ozone layer, high above our heads in Hansjörg Schlaepfer the atmosphere, whereby it is sorted out while the rest passes freely down Front Cover to us earthlings: our existence de­ A pilgrim transcending the medi­ pends most fundamentally also on eval lore is shown in this magnifi­ the processes taking place hic et cent wood engraving first published nunc in our cosmic front yard. These in L’atmosphère: météorologie populaire, are but two examples of a chain of by Camille Flammarion, Paris 1888. events in the history of the universe The original is attributed to an to which humans are just one re­ anonymous artist at the beginning sponse of Nature. of the Renaissance.

SPATIUM 24 2 COSMIC VISION1 Hansjörg Schlaepfer, Brissago

ESA was founded in 1975 not least Introduction based on the initiative of Swiss • How did everything begin? ­scientists and politicians to foster European efforts to explore space • What are the basic laws of One might think that scientists for peaceful purposes. From the physics? know what is to be known about very beginning, space research has • Are we really alone? the universe. Since the dawn of been the very core of ESA and mankind, humans have looked at the overwhelming success of its • What makes the solar system the sky and tried to understand the ­scientific spacecraft has won it tick? mysterious world out there. Thou­ worldwide acknowledgement as sands of years ago, an early society one of the leading space agencies. erected the gigantic stones in Stone­ henge, Great Britain, exactly in line With the intention of harmonizing Obviously, these questions are not with the midsummer sunrise. Four the endeavours of European aca­ specifically European; rather they hundred years ago, Galileo Galilei demic and industrial communities, are of interest for thinking humans directed his cannochiale to the sky the Agency formulated the Hori­ all over the world. It is, therefore, that uncovered a world never seen zon 2000 long-term plan for space one of the key elements of the Cos­ before by human eyes. Fifty years ­science in 1984 that defined the pri­ mic Vision plan to seek co-opera­ ago, Sputnik I initiated a new era orities and programmes for the sub­ tion with other space agencies in that led to today’s fleet of spacecraft sequent 10 to 20 years. Its succes­ order to not only benefit from the rushing through space in search of sor, the Horizon 2000+ plan, was experience and skills gained else­ new discoveries. All these en­ approved ten years ago; it consti­ where but also to share the costs of deavours are nourished by the fas­ tutes the programmatic foundation the anticipated missions. Beyond cinating results of space research of the scientific satellites and space paving the way for fascinating re­ that still do not become increasingly telescopes currently in orbit. Build­ sults, the Cosmic Vision programme sparse, but rather increasingly excit­ ing on past success to address the therefore contributes also to fur­ ing: Nature’s wealth of mysteries is scientific, intellectual and techno­ thering the understanding of boundless. logical challenges of tomorrow, ­scientists and ­engineers all over the ESA made another planning cycle world. Now then, what are the remaining in the first years of this new millen­ secrets of the universe scientists nium which resulted in the Cosmic would like to know? Where do they Vision plan outlined in the present expect the most enlightening dis­ issue of Spatium. It is basically built coveries to be made in the years to around the following four main ar­ come? What are the key questions eas of space research: that the European Space Agency (ESA) intends to address in the fu­ ture? The present issue of Spatium aims at providing some answers to these questions.

1 The present issue of Spatium is loosely based on a lecture given by Professor David Southwood for the Pro ISSI audience on 24 March 2009 and reported by Dr. Hansjörg Schlaepfer, Brissago.

SPATIUM 24 3 The Early Universe most phantastic results of recent How Did Every- space research to probe this first thing Begin? The Big Bang model is a physical light and to observe the universe in concept of how the universe might its earliest infancy. have come into being4,5. It has won wide acceptance as it is firmly This light is called cosmic micro­ OMNIUM RERUM ­underpinned by observations one wave background radiation as it PRINCIPIA PARVA SUNT2 can make today. Yet, it fails to de­ presents itself today as a microwave scribe the very earliest – and most radiation from all over the sky. It was Marcus Tullius Cicero3 crucial – instances when time, en­ found accidentally by Arno Penzias6 ergy and matter were born. At that and Robert Wilson7 with a ground- moment, the physical properties of based detector in 1964. While ini­ This is admittedly not quite a new the emerging universe exceeded by tially it was thought to be isotropic, question. Rather, generations be­ far the grasp of our understanding. later spacecraft equipped with more fore us have wondered already Some split second later, however, it sensitive ­instruments revealed tiny about how this world might have expanded and cooled down and its radiation (or equivalently tempera­ come into being. Great thinkers in parameters entered the reach of ture) differences in the order of all cultures have made their specu­ contemporary physics; from now 0.000,1 °C, see Fig. 1. The point here lations ranging from the cyclic on, the evolution of the universe is that these early fine structures are ­upcoming of what has been here becomes understandable. Not quite, essential for our existence as a per­ forever to a universe with both, a however, as we will see later. fectly homogeneous universe would definite beginning and a definite be unable to form inhomogeneities end. Cosmology, today, advocates a such as stars and planets. definite beginning, as described by The First Light the Big Bang model, while the The primary inhomogeneities stem ­future of the universe is still under A few minutes after the Big Bang, from quantum fluctuations in the debate. neutrons combined with protons to very early universe, which grew form the first deuterium and he­ with time to macroscopic structures lium nuclei. These are the first by gravitational attraction. How­ building blocks of matter as we ever, the visible matter in the uni­ know today. About 380,000 years verse is insufficient for that process, later, the temperature had cooled so scientists have to resort to what down to a value that allowed these they call Dark Matter8 to explain nuclei to bind electrons resulting in these fine structures. Dark Matter the first neutral atoms. That was a designates a hypothetical form of great event as it permitted light to matter that cannot be seen with propagate freely through space from electromagnetic waves – hence the now on: the universe became trans­ attribute dark – but can be inferred parent. It is certainly one of the from its gravitational pull on visible

2 Fr ee translation: the beginnings of all things are small. 3 Mar cus Tullius Cicero, 106 BC, Arpinum, today Italy, – 43 BC, Formia, today Italy, Roman politician and philosopher. 4 See Spatium 1: Entstehung des Universums, by J. Geiss. 5 See Spatium 3: Birth, Age and the Future of the Universe, by G. A. Tammann. 6 Ar no Allan Penzias, 1933, Munich, American physicist and Nobel laureate in physics 1978. 7 Rober t Woodrow Wilson, 1936, Houston, USA, American astronomer and Nobel laureate in physics 1978. 8 See Spatium 7: In Search of the Dark Matter in the Universe, by K. Pretzl.

SPATIUM 24 4 matter. A random distribution of The spacecraft consists of a service Gravitational Waves Dark Matter in the early universe module containing the necessary could explain the clumping of infrastructure and communication While it is an astounding undertak­ ­matter seen as fine structures in the elements and a payload module ing to explore the fledgling uni­ cosmic microwave background ra­ with a 1.5 metre telescope. verse, scientists would like to go diation. Since the nature of Dark back even further, right to its be­ Matter is still unknown, this unsat­ Currently, the spacecraft is under­ ginnings, when time, space and isfactory ad-hoc explanation con­ way to its destination 1.5 million matter saw the light of the day. Ob­ stitutes one of the major challenges kilometres away from the Earth, op­ viously, however, electromagnetic for scientists. posite to the Sun where it will be waves cannot do it as they were shielded from solar radiation by the continuously scattered by the hot Not surprisingly, the cosmic back­ Earth’s shadow. Here, its telescope plasma filling space during the ground radiation is amongst the will operate at a temperature of ­earliest epoch. Fortunately, there is universe’s most attractive objects –230 °C, and a sophisticated cryo­ another option emerging: as early and progress in space technology genic cooling system will keep the as some one hundred years ago, has been used repeatedly for new detectors close to absolute zero, i. e. ­Albert Einstein10 postulated the ex­ attempts to uncover its secrets. at –273 °C. Such exotic operating istence of tiny vibrations of gravi­ Treading in the footsteps of Rus­ temperatures are required in order tation, called gravitational waves. sia’s Relikt, NASA’s Cosmic Back­ to reach the sensitivity set by astro­ Gravitation is the phenomenon by ground Explorer (COBE) and the physical limits. The detectors will which objects with mass attract one Wilkinson Microwave Anisotropy be able to resolve temperature dif­ Probe (WMAP), ESA launched the ferences in the cosmic background Planck spacecraft on 19 May 2009, a in the order of one millionth °C by Fig. 1: The early universe based on NASA’s Wilkinson Microwave cornerstone of its horizon 2000+ far exceeding the specifications of Anisotropy Probe. The image reveals programme. The mission is named ­earlier missions. In addition, Planck 13.7 billion year old temperature fluctu­ after the German physicist Max will be the first spacecraft to observe ations shown as colour differences that Planck9, who derived the famous the polarization of the background correspond to the seeds that later grew to ­become the galaxies. The image shows Planck distribution of black-body radiation. a temperature range of ± 0.0002 °C. radiation. (Credit: NASA)

9 M ax Karl Ernst Ludwig Planck, 1858, Kiel, Germany – 1947, Göttingen, Germany, German physicist and Nobel Prize laureate in 1918. 10 Albert Einstein, 1879, Ulm, Germany – 1955, Princeton, USA, German-born Swiss Nobel Prize laureate in 1921.

SPATIUM 24 5 another. In our daily life, the Earth’s We shall return later to this fascinat­ learn that the universe has entered gravity lends weight to objects with ing subject when it comes to chal­ a new phase of accelerated expan­ mass. If now these masses move, like lenging our present day’s physics. sion. Newtonian laws of gravitation for instance a planet orbiting the would predict that the expansion is Sun, then their gravitation field slowed down continuously as a con­ moves as well. In Newton’s theory Cosmic Inflation sequence of the gravitational pull of gravity, the gravitational interac­ caused by matter. If the matter den­ tion between two bodies is instan­ As stated above, the Big Bang model sity in the universe were above the taneous. According to Einstein’s law is a powerful tool to describe the critical threshold, then the universe of special relativity, however, this is evolution of the early universe. Yet would finally collapse. On the other impossible, because the speed of Nature does not lend itself to sim­ hand, it would expand forever – light represents the limiting speed ple physical concepts: the Big Bang ­albeit at a decreasing rate – if the for all interactions. This leads to the model fails to explain why some matter density were below that concept of gravitational waves that tiny fractions of a second after the threshold. Now, extensive observa­ propagate through space at the speed beginning, the expansion rate of the tions of distant galaxies made in of light, see Fig. 2. According to universe experienced a sudden ex­ ­recent years brought the striking ­theoretical calculations, such varia­ ponential boost. This phase is called news: the universe has again entered tions are extremely faint and this is cosmic inflation, but it is not known a phase of accelerated expansion. probably why they could not be what caused this rapid expansion. While Dark Energy is thought to measured directly so far. Yet, they Like in the case of the Dark Mat­ be the responsible agent in this case, should possess the outstanding ter, scientists have to resort to an il­ too, the underlying physics remain ­feature as compared to electro-mag­ lustrative term describing the driv­ unknown. Even worse: both to­ netic waves of not being absorbed ing force behind comic inflation: gether, Dark Matter and Dark En­ by matter. Thus, one expects them Dark Energy11. Again, the name is ergy seem to dominate the universe. to allow for a glimpse back right telling but the underlying physics This brings us to the harassing in­ through the plasma in the earliest are not yet clear. sight that the world consists mainly universe. But this is still a long way of constituents that we can neither off: neither has their existence been While this early inflation has been see nor do we know what they are. proven experimentally so far nor are known for some 30 years, it came Once again: Nature’s wealth of mys­ the required technologies available. as the greatest surprise recently to teries is boundless.

Fig. 2: Two merging black holes ­generating gravitational waves. Implemented on a powerful supercom­ puter, Einstein’s theory of general relativ­ ity yields this magnificent portrait of a field of gravitational waves. (Credit: Chris Henze, NASA ARC)

11 See Spatium 20: What the Universe Consists of: from Luminous to Dark Matter and Quintessence, by U. Wiese.

SPATIUM 24 6 The Universe Taking Shape consist of a very large telescope, and their planetary systems. By this much larger in any case than the process, the universe gets increas­ Black Holes ­dimensions of available and future ingly richer in heavier elements and launcher payload fairings. There­ poorer in the light primordial at­ The chain of open questions does fore, special articulation technolo­ oms, but the current small relative not stop here; rather, recent obser­ gies will be needed to deploy the amount of heavier elements shows vations show that the centres – at optical system in space. that the process of element forma­ least of the majority – of galaxies tion is still in its infancy. In order to (including our own Milky Way) are understand the complex life cycle occupied by massive black holes. A The Evolving Violent of matter, an urgent requirement is black hole is a region of space where Universe to trace the history of black holes the gravitational field is so strong together with their host galaxies that nothing, including light, can es­ The Big Bang produced a meagre that contain the stars producing the cape its pull. It has a one-way sur­ cocktail containing only two com­ heavier elements. Technically speak­ face, called an event horizon, into ponents: hydrogen and helium, fla­ ing, this means that the environ­ which objects can fall, but out of voured by minor traces of other iso­ ment of black holes has to be ob­ which nothing can come. The ob­ topes12. This mixture is in sharp served in the x-ray and gamma ray servations made so far seem to in­ contrast to the rich variety of chem­ regions of the electro-magnetic dicate that black holes are instru­ ical elements we find today, which spectrum as matter accreted by mental for the formation and is a conditio sine qua non for the com­ black holes emits radiation at these evolution of galaxies due to their plex molecules necessary for Earth- wavelengths. An additional objec­ powerful gravity field, but it is not like planets and living systems. What tive of IXO is therefore to observe known how black holes are formed, then produces the additional chem­ black holes to understand the proc­ nor is it known how they interact ical elements? All heavier elements esses producing the wealth of chem­ with their host galaxies during for­ are cooked in stars, and debris es­ ical elements in the universe. mation. As galaxies are amongst the caping from the violent explosion building blocks of the universe, the of super massive stars disperse them understanding of black holes is into the interstellar medium, see Fig. 3: The remains of an exploded star. The Crab nebula is the result of a deemed instrumental for the under­ Fig. 3, where they are eventually supernova seen in 1054. It spans about standing of the cosmos at large. ­collected by newly emerging stars 10 light-years. (Credit: ESA/NASA)

In order to study the history of gal­ axies back to their formation ep­ och, a dedicated mission has been proposed, called the International X- Ray Observatory (IXO), a successor mis­ sion to earlier and most successful programmes. IXO is intended as a joint endeavour between the Euro­ pean, the US American and the Jap­ anese space agencies to capitalize on the experience gained world-wide so far. It is expected to launch around 2020. IXO will basically

12 See Spatium 13: Woher kommen Kohlenstoff, Eisen und Uran? by R. von Steiger.

SPATIUM 24 7 When it comes to understanding concept refers to the observation of What Are The the processes in space, laboratory matter under extreme conditions ­Basic Laws of physics suffers severe limitations as like for instance in the vicinity of the relevant parameters may be or­ black holes as described earlier Physics? ders of magnitudes outside the which then would constitute a fur­ range reached in conventional ther task of the IXO mission. An al­ laboratories. ternative approach implies the test of current physical models with the DUBITANDUM AT ultimate precision allowed by the VERITATEM13 Exploring the Limits of then available technologies. This Contemporary Physics might lead to discovering deviations Thomas of Aquinas14 between prediction and observation There are several possible routes and hence give indications where ­towards space physics. One can try current physical models suffer defi­ Physics, as it stands today, is the to simulate the relevant physical ciencies. Space again is the ideal lab­ ­result of generations of scientists’ conditions in ground-based labora­ oratory for this approach: Earth-or­ endeavours to try to understand tories. This is the approach taken by biting spacecraft can offer platforms Nature. The outcome of careful ob­ the European Organization for Nu­ that are extremely quiet, orders of servations was distilled into laws clear Research (CERN) in Geneva. magnitude better than Earth-bound that were probed subsequently by The new Large Hadron Collider laboratories that are subject to vi­ different, and often more elaborate, (LHC) will accelerate particles to brations from tectonic (and possi­ experiments. Many times, these ex­ the highest energies reached so far bly human) activities. In addition, periments confirmed the validity and bring them to collision with some experiments may require ex­ of the newly found theory, but – each other. Although the energy treme cryogenic conditions difficult and those are the truly interesting levels will be several orders of mag­ to reach on Earth and last but not cases – sometimes Nature did not nitude below those in the Big Bang, least space offers the dimensions do what was expected from her and there is justified hope to get impor­ making new types of experiments consequently the theory had to be tant indications where the weak­ feasible. discarded and replaced by a supe­ nesses of current physical models rior one. By necessity, these ex­ reside. In such marvellous space-borne periments were mostly made in laboratories one can challenge the ­laboratories i. e. in Earth-bound en­ On the other hand, space provides basic laws of physics, such as for ex­ vironments. This, however, has the natural laboratory for develop­ ample Galilei’s theory finding that ­major implications: the range of ing space physics15. The advent of all objects fall at the same rate in a ­environmental conditions in terms space technology has indeed al­ common gravitational field, see of pressure, temperature, gravity, etc. lowed scientists to exploit space as Fig. 4. This is the objective of a mis­ that are achievable by technical their new laboratory. This wider ap­ sion proposal called Galileo Galilei. It means is limited. The physics result­ proach would cover laboratory consists of test masses of different ing thereof could be termed labora- physics as a special case but include material encaged in a spacecraft that tory physics with its laws valid within and correctly describe the processes is held drag-free, i.e. shielded from the achievable range of physical pa­ in space as well. This approach may any acceleration caused by residual rameters but not necessarily outside. take two alternative forms. One matter in space and by the pressure

13 freely translated: through doubts towards the truth. 14 Thomas of Aquinas, ca. 1225–1274, philosopher and theologian in the tradition of scholasticism. 15 See Spatium 14: Grundlagen der Physik im extraterrestrischen Test, by M. C. E.Huber.

SPATIUM 24 8 of sunlight. In this environment, the behaviour of different test masses will be monitored which eventually could reveal any so far unknown gravity-like force acting differently on different material.

Another mission proposal, called Einstein Gravity Explorer, deals with clocks: Albert Einstein postulated that under the effect of gravity, time is stretched. Therefore, all clocks must experience the same effect by running slower with increasing gravity but it is not known whether different types of clocks are affected the same way. This is not merely a theoretical oddity but rather most relevant for satellite navigation sys­ tems such as the US Global Posi­ tioning System GPS or the Euro­ pean Galileo system.

These are only two examples amongst an impressive multitude of proposals made by the European physics community in response to ESA’s Cosmic Vision 2015–2025 call for proposals. Availability of technological and financial re­ sources as well as partnership op­ portunities will play a decisive role when it comes to implementing one or any of these ideas.

Fig. 4: A beautiful legend states that Galileo Galilei found the law of free fall while visiting the leaning tower of his home town Pisa around 1590.

SPATIUM 24 9 The Gravitational Wave and sensitivity. In the nineties of the is to prepare the required techno­l­ Universe last century, space-borne telescopes, ogies for detecting and exploiting like for instance the magnificent gravitational waves. Based on the Up to now, most information from Hubble Space Telescope, made a further experience gained, the subsequent space reached us via electro-mag­ major step allowing scientists to step will be the launch of the Light netic waves. Before Galileo Galiei, overcome the limitations set by the Interferometer Space Antenna (LISA) it was the naked eye that observed Earth’s atmosphere. Yet the limita­ mission proper around 2018, see the stars. Then, telescopes brought tions of electro-magnetic waves Fig. 5. a quantum leap regarding resolution remained. Basically, LISA consists of three As indicated above, replacing elec­ identical test masses placed on an Fig. 5: Artist’s concept of the Laser tro-magnetic waves with gravita­ equilateral triangle with an arm’s Space Antenna (LISA) mission. This programme aims at detecting gravita­ tional waves could open a com­ length of 5 million kilometres. tional waves from a variety of cosmic pletely new window to the universe. These test masses are free-floating sources. The concept calls for three iden­ As this subject is currently of highly in spacecraft that shield them from tical spacecraft orbiting the Sun on an speculative character, ESA together any adverse effects in interplanetary equilateral triangle with an arm’s length of 5 million kilometres. They each con­ with NASA has defined a step-by- space. Any tiny modulation of the tain two test masses which under the step approach where each step gravity field caused by gravitational ­effect of gravitational waves experience ­contains manageable risks. The first waves will cause the test masses to vibrations that will be a measure for the local strengths of the gravitational waves. milestone is the LISA Pathfinder mis­ individually follow the local grav­ (Credit: ESA/NASA) sion set for launch in 2011. Its scope ity gradient. The distances between the test masses are monitored with nanometre precision (10–9 m) using highly accurate laser-based tech­ niques. Although LISA might not be able to detect gravitational waves originating from the Big Bang, it will detect other sources, such as black holes and merging binaries (two stars orbiting around their common centre of mass) and thus constitute a crucial cornerstone in the research of this new category of waves and an important test of Ein­ stein’s general relativity. A later space mission (scheduled for the 2015 to 2025 time frame) will then specifi­ cally address the primordial gravi­ tational waves that emanated from the Big Bang.

SPATIUM 24 10 Are We Really From Gas and Dust to solar system. The solar mass was suf­ Stars and Planets ficiently high as to ignite nuclear Alone? fusion proc­esses in its core, where Earth is our place in the universe. the ­hydrogen stemming directly The Sun together with the Earth from the Big Bang is fused to he­ CHANCE AND NECESSITY and the other planets condensed out lium in a chain of thermonuclear of a large proto-solar nebula of in­ reactions. The tremendous energy Jacques Monod16 terstellar gas and dust some 4.6 bil­ output from these processes caused lion years ago17 (see Fig. 6). While the young Sun to shine: a new star the evolving Sun grasped by far the was born. Life on Earth evolved along random greatest part of nebular matter, some modifications of genetic material was left over and subsequently ag­ on the microscopic level and sub­ gregated to the other members in The Earth’s Biography sequent tests for usefulness on the the solar system, such as planets, as­ macroscopic level. Such modifica­ teroids and the uncountable smaller Meanwhile, the later Earth was a tions occurred without finality, just bodies towards the outer rim of the hot ball of liquid matter made up by chance, whereas their results had from chunks in the evolving proto- to satisfy the necessity for higher solar nebula. The heavier elements, ­reproduction success in order to like iron, migrated towards the ­become established. These basic Earth’s core, while the lighter ele­ mechanisms governing the evolu­ ments, like silicon, floated up to the tion of life are well-known. In surface. The latter solidified when ­contrast, the emergence of systems the Earth cooled down sufficiently capable of self-reproduction from thereby forming the first continen­ an abiotic environment remains a tal crust. The iron core for its part great mystery. Today, we are in a generated the Earth’s magnetic field unique moment of history where that shields us today so efficiently the technological means become against the solar wind and the Sun’s available to exploring other places deadly stream of high energetic in the universe for life. Are we ­really particles. alone? We still do not know it, but space research is addressing this old Initially, there was no atmosphere as question with stunning new means. the Earth’s gravity is too weak to hold the two most abundant gases in the proto-solar solar nebula, ­hydrogen and helium. The intense solar wind swept them off out to space. In contrast, the heavier vol­ canic gases emanating from the Earth’s interior, like methane, Fig. 6: In the Great Nebula of Orion new stellar systems are forming in gigantic clumps of gas and dust. (Credit: J. Bally, D. Devine & R. Sutherland, D. Johnson, HST, formed the early atmosphere. Yet it NASA) was devoid of oxygen, and therefore

16 Jacques Lucien Monod, 1910, Paris – 1976, Paris, French biologist, Nobel Prize laureate 1965. 17 See Spatium 6: From Dust to Planets, by W. Bentz.

SPATIUM 24 11 also of ozone that is generated from nia, its oxygen content steadily in­ vivors were able to pass on their ge­ oxygen by the ultraviolet radiation creased to reach values as high as netic heritage to later generations. of the Sun18. ­today already some 500 million years ago. It was at that time, in the Some 4.3 billion years ago, the Cambrian period, that life generated Life in the Universe Earth’s surface temperature fell be­ most of the current divisions of life low 100 °C allowing the first oceans in a relatively short time period. The Equipped with what we know of liquid water to form. About 500 availability of oxygen seems to about the evolution of life on Earth, million years later, the young Earth, have been one of the key conditions we can now embark on the search like all inner planets, underwent a for the emergence of new, and for life in the universe. Obviously, a dramatic phase of heavy bombard­ more complex organisms as oxygen first prerequisite is a planet within ment by large interplanetary chunks breathing provides much more the habitable zone around its cen­ of matter. The great maria such as ­energy than anaerobic processes. tral star. The habitable zone is de­ Imbrium or Serenitatis still visible Moreover, the Sun’s ultraviolet fined as the space around a star on the Moon’s surface bear testi­ ­radiation could now produce an where water on a planet can exist mony for those violent days. One ozone layer from the atmospheric in liquid form; not too close, as the of the most intriguing puzzles in oxygen which in turn provided an star’s heat would evaporate the wa­ Earth’s long history is that life seems efficient shelter against the parts of ter, and not too far, as the star’s ra­ to have emerged shortly after this the sunlight that can alter genetic diation would be too feeble and the cataclysmic period. Possibly, the material. The higher genetic stabili­ty water would freeze. Until 1995, it heavy impacts provided the ­required reached thereby may have given a was not known whether planets energy and chemistry for complex further boost to the evolution of ­really exist around stars outside the organic molecules to build up19, 20. more complex organisms. solar system. It was therefore a great discovery when Michel Mayor21 Since then, uncountable new spe­ and Didier Queloz22 of the Univer­ The Emergence of Life cies emerged, of which, however, sity of Geneva announced their de­ the greatest part were erased by cat­ tection of the first planet orbiting After its first emergence, life did not astrophic events: the history of life another star. Advances in observa­ make much progress for eons, al­ on Earth is a history of repeated tion technology have since allowed most two billion years. Certainly, mass extinctions. These may have detection of more than 300 such early organisms interacted with been caused for example by dra­ exoplanets. Although the currently and influenced their environment matic temperature declines leading known exoplanets are mostly large thereby unintentionally paving the to an Earth covered with ice, or by gaseous planets, like Jupiter, which way for later, higher forms of life. the impact of large meteorites that are unsuitable for life as we know One striking example is the atmos­ stirred up so much dust into the at­ it, they confirm the existence of phere. In the beginning it contained mosphere that only small remain­ planetary systems around sun-like no oxygen. Then, cyanobacteria and ing amounts of sunlight could reach stars and it is most probably a ques­ other organisms released oxygen as the surface and support life there. tion of further progress in technol­ a waste product of their metabolism In spite of all these setbacks, never ogy to find Earth-like planets as into the atmosphere. Over millen­ were all species extinct, and the sur­ well.

18 See Spatium 21: Ozone, by Y. Calisesi. 19 Roger M. Bonnet and Lodewijk Woltjer: “Surviving 1,000 Centuries”, ISBN 978-0-387-74633-3. 20 See Spatium 16: Astrobiology, by O. Botta. 21 Michel Mayor, 1942, Echallens, Switzerland, Swiss astronomer at the University of Geneva. 22 Didier Queloz, 1966, Swiss astronomer at the University of Geneva.

SPATIUM 24 12 Recently23, the joint CNES/ESA From Exo-Planets to it consists of probing the atmos­ programme Corot detected an ob­ Biomarkers phere of an exoplanet for biomark­ viously rocky exoplanet less than ers. Spectroscopy is the preferred twice the size of Earth orbiting a Today, observation technologies fac­ observation method as the emission sun-like star. In fact, such a planet ilitate the discovery of exoplanets spectra of gases are excellent foot­ could harbour life. The Corot and allow researchers to make an prints for identifying them where­ ­mission was launched in late 2006. estimation of their orbital para­ ever they are throughout the It consists of a telescope specifically meters and their masses. But they ­universe. Thus, the required tech­ designed to observe planetary tran­ do not provide any information re­ nological principles are basically sits. This method is based on detec­ garding possible biological activities known. The outstanding challenge, ting a planet by the small drop in on the exoplanet. To get a step for­ however, resides in the fact that the the brightness of a star during the ward, one must first try to define radiation of the star is by orders of phase when the planet covers a what the term life could designate. magnitudes greater than that of the small part of the star’s disk. Unfortunately, life is by far too exoplanet and the distance to the complex an entity to be seized by a nearest star is in the order of 4 light definition; thus, we find ourselves years, i. e. some 1013 kilometres from in the embarrassing situation of the Earth. Looking for exoplanets searching for something we cannot is like trying to see the difference define. To overcome this dilemma, between the feeble light from a astrobiologists have defined a set of ­candle next to a lighthouse from a biomarkers that are substances used point 1,000 kilometres away. This as indicators for biologic processes. task is by far beyond present-day Based on the history of life on technologies; rather, it is expected Earth, oxygen and methane are that the required means might be ­accepted as the most important bio­ developed by 2030 making a spe­ markers. This is – it must be admit­ cific terrestrial planet finder mission ted – a very Earth-centric definition feasible. But there is still a long way of biomarkers that could possibly to go. exclude finding different forms of life. Engineers and scientists design­ In the meantime, ESA is studying ing new space missions will cer­ the Darwin mission, a flotilla of four tainly open the scope of their or five spacecraft designed to search ­instruments sufficiently to detect for likely places for life outside the other forms of biological activities solar system. Darwin will survey as well. some thousands of the nearest stars, look for small, rocky planets and Lacking a wider view on what life probe their atmospheres for the is, the search for extraterrestrial life most relevant biomarkers. While begins with searching for biomark­ one spacecraft will act as a central ers in the universe. More precisely, communications hub, the others

23 ESA News, 3 February 2009.

SPATIUM 24 13 will function as light collectors that Life and Habitability in the in the Martian atmosphere that can­ redirect the light collected by their Solar System not be explained by known atmos­ telescopes to the central hub space­ pheric chemistry and physics. In craft. Here, the different beams will Mars ­addition, these methane concentra­ be superimposed and processed in Some promising places within our tions seem to overlap in some re­ a way that allows the flotilla to own solar system await inspection, gions with concentrations of water ­simulate a single telescope with the which are much closer to us than vapour. This could be interpreted as aperture roughly the size of the dis­ exoplanets. Mars is one of the most stemming from a common under­ tance to the light collector spacecraft. auspicious addresses. Probably, the ground source which in turn would Such large apertures are mandatory Red Planet hosted an atmosphere provide important new hints to to image exoplanets and probe their that disappeared some one billion evaluate the hypothesis of present atmosphere; interferometry is used years ago. The planet’s surface is full life below the surface of Mars. to cancel out the light of the much of erosion patterns that resemble brighter central star. Exhaustive pre­ those generated by rivers on Earth. ESA has bundled its forthcoming paratory work on technology de­ These are telling signs of abundant Mars exploration programme un­ velopment is required before it be­ liquid water in a distant past. We do der the heading Aurora. One of its comes even feasible to set up a not know, why the atmosphere dis­ key missions is Exo Mars intended to schedule for the Darwin mission. appeared and left the Martian sur­ explore promising sites on Mars face a dead desert and whether with a robotic vehicle. The mission ­similar processes could deprive the calls for the development of a Mars Earth from its atmosphere – with orbiter, a descent module and a dramatic consequences for its Mars rover. The Mars orbiter is to biosphere. reach Mars and put itself into orbit around the planet. On board is a Mars has been a favourite destina­ Mars rover within a descent mod­ tion of spacecraft since the early ule. The Mars descent module will Fig. 7: ESA’s Mars Rover is shown in this artist’s view drilling a hole in the days of space programmes. NASA deliver the rover to a specific loca­ Martian surface in search of subsurface has sent an armada of orbiters and tion. The rover (see Fig. 7) is in­ life. (Credit: ESA) robotic rovers to the Red Planet. tended to travel a few kilometres ESA launched the Mars Express over the planet’s rocky surface and spacecraft in mid 2003. The space­ to operate autonomously by using craft reached its destination six onboard software and optical sen­ months later and has orbited the sors. Its main mission objective is to planet since. Although its design life search for signs of past or present has been completed it continues to life. To this end, it carries a 40 kilo­ monitor the planet’s surface suc­ gramme exobiology payload in­ cessfully. The spacecraft is equipped cluding a lightweight drilling sys­ with a high resolution stereoscopic tem with a reach of 2 metres below camera that delivers outstanding the surface. Launch is scheduled for imagery and elevation information. 2013. In addition, it disposes of a sound­ ing radar that maps the sub-surface The next milestone in the Aurora structure to a depth of a few kilom­ programme will constitute the etres in search of water and ice. launch of the challenging Mars Sam- ple Return mission in the 2020–2022 Recently, its spectrometer instru­ time frame. This spacecraft is com­ ment observed patterns of methane posed of several modules serving

SPATIUM 24 14 the flight to Mars, the landing on as our Moon. It possesses a tenuous one spacecraft. ESA will provide the its surface, collecting samples at atmosphere containing oxygen. Its ­Jupiter Planetary Orbiter to probe promising sites and conserving surface is a relatively young icy planet Jupiter, NASA will be re­ them in a contamination-secure crust, see Fig. 8. Europa is probably sponsible for the Europa orbiter, container which then are returned heated internally by Jupiter’s strong while JAXA’s share will consist of back to Earth. Before implement­ gravitational field which could keep the Jupiter Magnetospheric Orbiter. ing such a complex mission profile, the ocean below the icy surface liq­ The three spacecraft will cruise a series of technologies need to be uid and drive geological activity, jointly to destination during 5 to prepared and tested in orbit first. both basic requirements for life to 7 years, and then separate to indi­ emerge there. vidually explore their objects. Cur­ rently, the Laplace mission proposal Moons in the Outer Solar In order to probe the potential is in the industrial assessment study System ocean on Europa for biologic activ­ phase. ity, it would be necessary to drill a As defined above, the habitable zone hole through the ice crust and to is the space around a star where liq­ operate a small life science labora­ uid water on a planet’s surface could tory there. Unfortunately, it is not exist. This is true as long as the ra­ known how thick the ice really is diation from the central star is the and if there is actually liquid water dominant source of energy. There below. So, the current status of in­ exist, however, additional sources formation about Europa’s internal that can produce enough heat to al­ structure and the technical chal­ low surface liquid water far outside lenges of such a mission do not yet the habitable zone. One such heat­ allow for the planning of a dedi­ Fig.8: Miraculous Europa. One of Ju­ ing mechanism is the strong grav­ cated mission in the next 20 years. piter’s moons, Europa is thought to pos­ ity field of a large planet operating Rather, intermediate steps are more sess an ocean of liquid water beneath its on a moon circling it on an appro­ realistic, such as for instance ESA’s icy surface. This image reveals character­ 24 istic surface ridges and cracks along with priate orbit. The changing position Laplace mission. domes and dark reddish spots. (Credit: of the moon in relation to the plan­ NASA). et’s gravity field gives rise to chang­ The Laplace mission is named after ing forces on the moon’s body the French astronomer Pierre-Si­ which in turn leads to tidal effects mon Laplace, whose work was piv­ on the moon. These tides cause in­ otal to the development of mathe­ ternal heating of the moon which matical astronomy. The purpose of can be a valid alternative to heating the mission is to explore the com­ by the Sun. plex Jovian system as a whole, with special emphasis on studying Euro­ Europa, one of Jupiter’s compan­ pa’s habitability in the global con­ ions, is one such mysterious world text of the Jupiter system. Laplace in the outer solar system. Discov­ is planned as a trilateral endeavour ered as early as 1610 by Galileo between ESA, NASA and the Galiei, Europa has a diameter of ­Japanese space agency JAXA. Each 3,100 kilometres, roughly the same of these participants will contribute

24 Pierre-Simon, marquis de Laplace, 1749, Beaumont-en-Auge, France – 1827, Paris, French mathematician and astronomer.

SPATIUM 24 15 What Makes The From the Sun to the Edge able for the first time to see solar of the Solar System storms building up over an ex­ Solar System tended period of time from the The Sun dominates the solar sys­ same viewpoint. The spacecraft will Tick? tem25. Its magnetic field is the source orbit the Sun in an elliptical orbit of the solar wind, a stream of parti­ that brings it as close as 0.23 AU27 cles that rush away to eventually to our daytime star, where it will THIS WORLD’S MOST meet with the interstellar medium26. experience 20 times the radiation ­INCOMPREHENSIBLE This is the edge of the solar system, intensity compared to that on the FACT IS ITS called the heliopause. The Sun also Earth. The intense solar radiation COMPREHENSIBILITY. emits, in events called solar flares, will therefore be Solar Orbiter’s main energetic particles that would be a design driver. The spacecraft will be Albert Einstein deadly threat to life on Earth if they three-axis stabilized and possess a were not efficiently shielded by the sunshield that will always be point­ Earth’s magnetic field that safely re­ ing towards the Sun to protect the Understanding the solar system is a directs them out to space. On the scientific instruments aboard against basic prerequisite for understanding other hand, both the solar wind the heat from the Sun. the universe. The solar system offers and the energetic particles carry so to say the playground where the valuable information regarding the Mercury cosmic processes can be observed composition of the Sun and the in a – relatively – convenient dis­ processes at its surface and in its co­ Next to the Sun is Mercury, an ex­ tance, be it by means of telescopes rona. This allows studies of regions tremely hot world, with surface or by space robots. In addition, the on the Sun that are not accessible temperatures up to 400 °C, as its or­ Earth’s cosmic environment, and es­ to in-situ exploration because of the bit is only between 0.3 and 0.46 AU. pecially the Sun, is the most impor­ excessive heat. Thus, the Sun has Due to the technological challenges tant with regard to our planet. So been a priority object for the first set by such conditions relatively lit­ putting a high priority on the ex­ generations of scientific spacecraft tle is known about Mercury. ESA, ploration of the solar system is more and it will remain so in future. together with JAXA, is currently than justified. preparing the BepiColombo28 mission In the frame of the Cosmic Vision scheduled for launch in 2014 with programme, ESA intends to launch arrival at Mercury some six years the Solar Orbiter mission to study the later after complex orbital manoeu­ Sun. Solar Orbiter, planned as a col­ vres around the Moon, Earth, Venus laborative effort with NASA, will and Mercury itself. It consists of two be the first satellite to provide close- individual spacecraft: the Mercury up views of the Sun’s polar regions Planetary Orbiter intended to map providing images from high lati­ the planet, and the Mercury Mag­ tudes. It will be able to tune to the netospheric Orbiter. Amongst the Sun’s rotation around its axis for instruments intended for Mercury several days, and it will therefore be exploration is the Laser Altimeter, a

25 See Spatium 2: Das neue Bild der Sonne, by R. von Steiger. 26 See Spatium 17: The Heliosphere, by A. Balogh. 27 1 Astronomical Unit (AU) equals 150 million kilometres, the distance between the Sun and the Earth. 28 Giuseppe Colombo (better known by his nickname Bepi Colombo), 1920, Padova, Italy – 1984, Padova, Italian scientist, mathematician and engineer.

SPATIUM 24 16 complex electro-optical instrument position, it is covered with an The Giant Planets and that emits light pulses towards the opaque layer of clouds of sulphuric Their Environments surface of Mercury, where they are acid, preventing its surface from be­ reflected and subsequently collected ing seen from space in visible light. Outside the orbit of Mars follow by the receiver. The Physikalisches It is thought that Venus once pos­ the gas planets Jupiter and Saturn, Institut of the University of Bern sessed Earth-like oceans in the past, both consisting mainly of hydrogen together with Swiss industry is cur­ but these have totally evaporated in and helium with probably a rocky rently involved in the design and the meantime. There are only a low core at their centre. Uranus and development of this instrument, number of impact craters on Venus’ Neptune, the outermost planets, are which will allow scientists to make surface, indicating that its surface is probably built up from an inner a detailed reconstruction of the relatively young, approximately half rocky core, enshrouded in an icy planetary surface. a billion years, and that strong mantle of water, ammonia and ­geological activity is continuously methane and a gaseous outer shell Venus reshaping it. of hydrogen and helium.

Mercury, together with Venus, Earth The Saturnian system was the and Mars are collectively termed Mars ­object of the most successful ESA/ the terrestrial planets, since they are NASA Huygens-Cassini mission all primarily composed of silicate Mars29 is the fourth planet from the which culminated in the landing of rocks like the Earth, in contrast to Sun in the solar system. The Red the Huygens probe on Titan’s sur­ the gas giants like Jupiter and Sat­ Planet is the destination of past, cur­ face on 14 January 200530. It has a urn and the outer planets Uranus rent and future space missions. Mars diameter of 5,150 kilometres and Neptune. Even though the ter­ research is strongly focused on the (roughly 50% larger than our restrial planets have many similari­ search for past or present life as de­ Moon). Its thick atmosphere is rich ties, they are very different: Venus, scribed above, but since Mars is one in organic compounds. Some of the second planet from the Sun, is of the four terrestrial planets, it them would be signs of life if they enshrouded in a dense atmosphere merits in-depth research per se as it were on our planet. The wealth of containing mainly CO2 with some helps us to understand our own data received by Huygens and Cas­ N2, but it has no magnetic field. This planet. In addition, its environmen­ sini answered many previously planet is currently being explored tal conditions are relatively favour­ strongly debated questions but, and by ESA’s Venus Express mission. The able for remote sensing and in-situ this is the fascination of science, it Earth in turn has both, an atmos­ exploration, quite in contrast to opened at least the same number of phere and a magnetic field, which Mercury and Venus. Mars possesses new questions, such as whether the are key prerequisites for the emer­ a rich variety of surface patterns organic substances on Titan will gence of life. stemming from meteorite impacts help us to discover how life began (craters), volcanism (calderas, volca­ on Earth. Venus Express has revealed many se­ noes) and erosion (possibly liquid crets about our Morning Star. While water), but also polar caps (frozen It is therefore not surprising that this planet is similar to Earth in CO2 together with possibly water scientists are currently planning a terms of size, gravity, and bulk com­ ice). further mission to probe the Satur­

29 See Spatium 5: Earth, Moon and Mars, by J. Geiss. 30 See Spatium 15: Titan and the Huygens Mission, by N. Thomas.

SPATIUM 24 17 nian system. To this end, ESA has Asteroids and Other Small built up good relations between Eu­ incorporated the TANDEM (Titan and Bodies rope and Asia. The mission scenario Enceladus Mission) in its Cosmic Vi­ calls for a mother spacecraft that is sion plan. It is intended to continue Most of the proto-solar nebula mat­ to carry out a global characteriza­ the research made by Huygens- ter was collected by the Sun and the tion campaign of the potential tar­ Cassini and specifically to carry out planets. The tiny remaining part get object. This process should de­ an in-depth investigation of the two thereof formed uncountable small liver information on all major most enigmatic Saturnian moons, bodies on a variety of orbits, mostly surface hazards on the NEO and Titan and tiny Enceladus. The lat­ far off the Sun. As leftover building determine the most scientifically re­ ter has been found to be an ex­ blocks of planet formation main­ warding sampling sites. Then, it will tremely exciting world. Its diame­ tained deep frozen since the begin­ release a lander and possibly a cou­ ter is of the order of 500 kilometres, nings of the solar system, they offer ple of small hoppers that will anal­ equivalent to only some 15% of the important clues to the chemical yse surface/sub-surface materials. Earth’s Moon. In its south polar re­ mixture from which the solar sys­ After a number of sampling rehears­ gion there are organic-laden jets of tem formed. als, the main spacecraft will finally water vapour and dust-sized ice touch down on the surface to particles emanating from the sur­ In order to explore these primor­ ­collect the sample. Thereafter, it will face, possibly from a liquid water dial objects, ESA has proposed the take off from the NEO and be reservoir just below the icy surface, Marco Polo31 mission together with placed on an Earth return trajectory, similar to Jupiter’s moon Europa JAXA with a possible launch date where it will arrive some five years described above. As liquid water is in 2017. The scope of this endeav­ after launch, to release its re-entry one of the key requirements for the our would be to collect and return capsule containing the samples. emergence of life as we know it, samples back from a Near Earth Marco Polo is intended to provide Enceladus is one of the few likely Object (NEO) such as a meteorite, the first opportunity for detailed places for life in the solar system. an asteroid (see Fig. 9) or a comet. laboratory study of the most pri­ The mission is named after one of mitive material in the solar system. the earliest western people who

Fig. 9: Asteroid Itokawa, recently vis­ ited by the Japanese spacecraft Hayabusa, exhibits a very rough surface interrupted by astonishingly smooth areas. It has an overall length of some 500 metres. (Credit: ISAS, JAXA).

31 Marco Polo, ca. 1254–1324, merchant of the Venetian Republic who made a pioneering journey to Asia that later opened the famous Silk Road.

SPATIUM 24 18 Conclusion legacy of their intellectual predecessors.

Yet, all research, space research not Since the dawn of mankind, hu­ excluded, has to pass some utility mans have looked at the sky and requirements in order to find the tried to understand the mysteries of tax payer’s consent. Certainly, one the cosmos. Space research and of the most influential results of space technology are the answer of space exploration has been the pic­ this generation to that old dream. It ture of our blue planet taken by the continues the work of the great Apollo 8 crew, some 40 years ago, ­earlier thinkers, from Aristotle to showing a fragile Earth surrounded Copernicus, Galilei, Newton, Ein­ by the immense dead void of space, stein and many others. In contrast Fig. 10. This image, together with to their day, however, space research later research results, has furthered has become today a complex under­ the perception of the finiteness of taking that exceeds by far the reserves on Earth and given rise to ­possibilities of one single person, growing concern about the use of and often even that of a nation. Ex­ the natural resources at the expense ploring the cosmos has become a of a vanishing diversity of life. truly global endeavour. Beyond ­delivering fascinating results, space May this issue of Spatium contrib­ ­research is a uniting agent for all ute to the readers’ awareness of the the people involved world-wide unique responsibility humans are in search of bringing further the given in Earth’s history!

Fig. 10: Earth-rise seen from the Moon. This wonderful image was taken by the Apollo 8 crew on mankind’s first journey to round the Moon in Decem­ ber 1968. (Credit: NASA)

SPATIUM 24 19 SPATIUM

The SPATIUM Series published by the PRO ISSI Association as of February 2010

1 Entstehung des Universums J. Geiss Apr 98

2 Das neue Bild der Sonne R. von Steiger Nov 98

3 Birth, Age and the Future of the Universe G. A. Tammann Jun 99

4 Kometen K. Altwegg Sep 99

5 Earth, Moon and Mars J. Geiss Jun 00

6 From Dust to Planets W. Bentz Nov 00

7 In Search of the Dark Matter in the Universe K. Pretzl Jun 01

8 Sun and Climate J. Beer Nov 01

9 The Fourfold Way Through the Magnetosphere G. Paschmann Jun 02

10 Satellite Navigation Systems for Earth and Space Sciences G. Beutler Jun 03

11 Cosmic Rays H. Schlaepfer Nov 03

12 Ten Years Hubble Space Telescope R. M. Bonnet Jun 04

13 Woher kommen Kohlenstoff, Eisen und Uran? R. von Steiger Nov 04

14 Grundlagen der Physik im extraterrestrischen Test M. C. E. Huber Jun 05

15 Titan and the Huygens Mission Nicolas Thomas Nov 05

16 Astrobiologie O. Botta Jun 06

17 The Heliosphere A. Balogh Oct 06

18 Einstein in Bern: The Great Legacy R. von Steiger Jan 07

19 4440: a Secret Number for Astronomy H. Schlaepfer Aug 07

20 What the Universe Consists of: from Luminous to Dark Matter and Quintessence U. Wiese Oct 07

21 The Earth’s Ozone Layer Y. Calisesi Jun 08

22 Solar Magnetism E. Parker Aug 08

23 Meteorites B. Hofmann Mar 09