RINCIPIUM PThe Newsletter of the Institute for Interstellar Studies ™

Introduction by Rob Swinney

News from the Institute

‘Advances’

‘Listening Post’

Retrospective: Voyager

Book Reviews R IN O T F E R E S T

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S ™ TUDIES Scientia ad sidera www.I4IS.org Knowledge to the Stars A letter from Rob Swinney

We do indeed live in exciting times. developing a core curriculum in I remember growing up in the sixties interstellar studies for students to and seventies and being totally captured provide them with the up-to-date by a similar spirit during the Apollo age academic training they will need to be and the later planetary missions. Sadly successful in this field. In the longer the dream of manned missions to Mars term we also intend to inspire and by the eighties and Saturn by the early develop students from as early as Key twenty-first century crumbled. The Stage 2 onwards and will undertake promise shown by the inspirational yet targeted public outreach events to give fictional worlds of Star Trek and Star them an understanding of space and its Wars seemed just that – fictional. many challenges. Now, once again, ‘the planets are lining Although the Institute's mission has up’. There is a new buzz. There is a a clearly defined goal, to achieve true feeling that the technologies required interstellar flight, we believe that in the to reach the stars are just on the horizon coming years the Academy will naturally (at least unmanned to start with). So a provide a cornerstone in the Science, few years ago, having attained the rank Technology, Engineering and of squadron leader as an aerosystems Mathematics (STEM) goals of the engineer in the Royal Air Force, I wider society. In addition we hope to decided to take my contractual option to encourage all aspects of understanding, leave. I was already reflecting on what from the related social and cultural great new adventure to take. Maybe you activities, the arts and fostering are too? imagination so that our graduates will be able to work co-operatively with anyone Having met the likes of the Institute’s from the global community and make a Executive Director Kelvin Long at the positive contribution. British Interplanetary Society’s meetings, it was through Project Icarus One of our greatest challenges is that that we came to work more closely we are initially a group of volunteers together, starting in 2009. When Kelvin working in our own time to build a told me of his plans for the Institute I strong foundation to the Academy and was immediately keen to get involved. the Institute. Our rapid growth has I didn’t realise that he had big plans for proven to be an organisational challenge me having known that I had spent a and only overcome by more hard work few years as a teacher and had also and time dedicated to the cause. We are been closely involved at the RAF’s fortunate that we have a growing College, running and instructing on number of people supporting our work. aerosystems engineering courses and Perhaps you would like to be involved being involved with the leadership with the Institute too? Enthusiasts are training of young officers. always welcome and you can reach us via our website, www.i4is.org. My role in the institute for Interstellar Studies will be the first Director of the This brings me to the recent sad Academy. We have big plans for the passing of Sir Patrick Moore, whom Academy to support the work of the I first met in the 1980s. He was Institute and have recently started with undoubtedly my favourite enthusiast, new interstellar themed MSc Projects. showing what could be achieved with Our first ‘customers’ are based with the great dedication and hard work. If the International Space University located in founders of the Institute can follow his Strasbourg with four students example we can look forward to a undertaking projects as part of their successful future. Space Studies course. Recently we even Thank you Patrick, RIP. had our first member travel from India to the USA to attend an international conference. We plan to develop this to Rob Swinney support the younger members of the Academy and Finance Director Institute and eventually create a full The Institute for Interstellar Studies™ scholarship programme. We are

Principium | Issue 2 | January 2013 Page 2 News from the Institute

Going interstellar in Tennessee Evacuate Earth! The Philosophy of the Starship National Geographic Channel explored Date: May 29th 2013 the possibility of interstellar travel before the end of the twenty-first century over Venue: BIS HQ 27/29 Lambeth Road, the Christmas period with their new docu- London drama, Evacuate Earth . With I4IS This is a symposium on the philosophy of Executive Director Kelvin Long onboard the Starship. At some point in the future, as a scientific consultant, Evacuate Earth focused on whether it would be possible to human kind will build robotic and human transport humanity to another star carrying vessels which will go beyond the system were Earth placed in jeopardy (in solar system, out into interstellar space the programme, from a rogue neutron and onto visit worlds around other stars. star on a collision course). As we prepare our civilization to embark Scientists, engineers, authors, on this exciting journey to establish the anthropologists and sociologists will be new frontier, it is worth pausing to think, heading to Alabama, United States in and consider how we should plan these February for the Second Tennessee Valley bold and ambitious missions. That Interstellar Workshop. It’s organised by planning begins now. NASA space scientist and science fiction History has shown examples of societies author Les Johnson – who’s book Going who built great vessels for similar Interstellar we reviewed last issue – and is purpose, such as the Portuguese Caravel being sponsored by several organisations Evacuate Earth: launching a starship from a doomed planet. sailing ships which were launched in the including the Institute for Interstellar Image: National Geographic. 1400’s and used for 300 years hence to Studies ™ and the British Interplanetary explore the coast of Africa. The Italian Society. There’s going to be a strong I4IS The show garnered a fair bit of media explorer Christopher Columbus set sail presence at the workshop, including attention, including a piece in the 21 across the Atlantic Ocean in an Kelvin Long and Claudio Maccone, as December edition of The Times , where expedition of three such ships in 1492, well as Centauri Dreams’ Paul Gilster and Long was interviewed about possible hoping to find a route to India to trade for Icarus Interstellar’s Richard Obousy. forms of starship propulsion and I4IS spices. His mission was funded by King given a mention in the newspaper – Ferdinand II and Queen Isabella of Spain. The aim of the workshop is to hopefully it is just the beginning of raising encourage discussion and debate and the Institute’s star in the media! The result was his discovery of the New promote thought-provoking ideas across a World. Similarly, HMS Challenger set out If you missed Evacuate Earth on the in 1872 on a three year scientific exercise wide-range of topics: spacecraft National Geographic Channel, you can propulsion technologies and engineering; catch it on YouTube at to lay the foundations of oceanography, economic, social and political http://www.youtube.com/watch?v=vFgJ7Hss1VA going on to discover 4,000 previously considerations; life support and unknown species. hibernation; colonisation concepts and I4IS Talks For the future Starships, what sort of exoplanet studies; and SETI. With the vessels should we send and what will be line-up of heavy-hitting speakers and Institute for Interstellar Studies Executive their function? how should they be attendees it’s going to be one not to miss Director Kelvin Long will be embarking on constructed, financed and governed? if you’re in the area. Held over 3–6 a lecture tour in the United States at the What sort of technology should such February 2013 at the Nexolve first floor beginning of February. Dates announced so vessels contain? What are the auditorium at 655 Discovery Drive, far include: risk/benefits for making the trip? What Huntsville, Alabama, USA, as part of the • Tennessee Valley Interstellar are the implications for the future workshop there will also be a tour of the Workshop, Huntsville, Alabama evolution of those star faring humans that United Launch Alliance facility where the (5 February) made the voyage? Who should go, why and workhorse Delta IV and Atlas V rockets • NASA Marshall Spaceflight Center, what characteristics should these Starship used by NASA are built. Meanwhile, the Huntsville, Alabama (6 February) humans have? What will we discover when results of the workshop will be published we get there? Do we understand what is in a special issue of the Journal of the • NASA Glenn Research Center, Cleveland, Ohio (8 February) meant by the romantic phrase “Starship”? British Interplanetary Society . The Institute for Interstellar Studies™ Kelvin also has two European dates lined has organized this symposium in For more details, visit up. First he'll be at the International Space http://lesjohnsonauthor.com/tviw/tviw_2013. collaboration with the Journal of the University in Strasbourg, France on 19–20 British Interplanetary Society. We invite February and then on the following innovative and thought provoking papers weekend of 23–24 February at the UKSEDS which explore these ideas. (UK Students for the Exploration & Devel- opment of Space) 2013 conference at the All submissions should be sent to University of Bristol. To keep up with [email protected] . Kelvin you can follow him on Twitter under All proceeds from running this 'thestarshipman' symposium will go to the British [https://twitter.com/thestarshipman ]. Interplanetary Society.

Principium | Issue 2 | January 2013 Page 3 ADVANCES Another potentially Earth-like planet?

Future interstellar explorers may have a new destination to head for: five rocky planets, including one at an equivalent distance from its star as Earth is from the Sun, just 11.9 light years away around the star tau Ceti.

The findings come from new analysis of old radial velocity data; in other words, the slight Doppler shift in the star’s light as it and its planets ‘wobble’ around a common centre of mass. The problem for low mass terrestrial exoplanets is that they produce very small radial velocity signals that can get lost in the noise. So a multinational team of scientists led by University of Hertfordshire astronomers have attempted to get around these limitations by coming up with a new modelling technique that they claim successfully reduces the noise in the data to reveal those tiny planetary signals. In a press release the team leader, Mikko Tuomi, describes a process of “adding artificial signals to the data and testing our recovery of the signals with a variety of different approaches. This significantly improves our noise An artist’s impression of a rocky exoplanet, perhaps like tau Ceti e. modelling techniques and increases our Image: ESO/M Kornmesser. ability to find low mass planets.” The team applied this technique to Sun meaning that the distance of the cases our approach has always been to go data from the three most sensitive region where an Earth-like planet with back to the telescope and confirm with planet-finding spectrographs in the an atmosphere can support liquid water further observations.” is closer in. Additionally, planet d is on world – the HARPS spectrograph at the After a recent flurry of unconfirmed the inner edge of this zone and could European Southern Observatory in terrestrial planets (including alpha perhaps resemble Venus. However, not Chile, UCLES in Australia and HIRES at Centauri Bb and HD 40307g, both everyone is convinced yet as to the the Keck Observatory in Hawaii. The reported on last issue) we stand either existence of the planets. most notable result indicates that planet on the cusp of a new age of planetary e, with a mass 4.2 times that of Earth, “[Their work] does not give, with science, or one of disappointment as the orbits tau Ceti every 168 days at a good probability, any final answer about planet claims are retracted. One thing is distance of just over 82 million the planetary content of the system, but for certain; with each new discovery of a kilometres. Although tau Ceti is the only a first guess,” says Stephane Udry of nearby exoplanet, the clamour for an closest star to share the Sun’s spectral the University of Geneva, who works interstellar mission grows. type (G), it is slightly cooler than our with the HARPS instrument. “In such

Did you know?

Tau Ceti was one of two stars surveyed by Frank Drake for extraterrestrial signals as part of his pioneering Project Ozma (the other star being epsilon Eridani) in 1960.

Principium | Issue 2 | January 2013 Page 4 Listening Post

To the Editor, years through radioactive decay of this is a likely outcome or not, it uranium, thorium and potassium, could remains another possibility that as yet Good science depends upon precision in then support sub-surface life wherever the use of language. For example, that world might happen to be located in cannot be excluded. Such systems would physics makes important distinctions interplanetary, interstellar or even both answer a general definition of life between energy and power, mass and intergalactic space. Many such worlds and be totally independent of Earth-like weight, force and momentum. must have been ejected from their surface conditions. If the scientific community is adopting parent planetary system during the Given that the terms ‘habitable zone’ populist expressions that are chaotic processes of planetary formation. and ‘habitable planet’ are therefore scientifically inaccurate, I propose that grossly misleading at our current state of the I4IS should lead the way in knowledge, I would suggest that the I4IS promoting a more precise use of lead the way in using terms that reflect language. This is especially important in more accurately what is actually meant. such an exotic subject as interstellar ‘Earth-analogue’ planet/zone would seem studies, whose concepts are often remote to be the most precise. Life may inhabit from popular understanding, even to the an Earth-analogue planet in the Earth- point that, in his 10 December posting analogue zone around its star, or it may on Centauri Dreams, Paul Gilster inhabit somewhere else, such as a sub- commented: “I still find myself having to surface region of a world like Europa or explain the difference between Titan, or a temperate zone in the ‘interplanetary’ and ‘interstellar’ at the atmosphere of a gas giant planet, or a oddest moments.” What makes a planet ‘habitable’? completely manufactured artificial We are seeing increasing use of the Image: NASA/JPL–Caltech/R Hurt world. Any of these alternatives could be term ‘habitable zone’ around a star, and (SSC/Caltech). found at different distances from a star. ‘habitable planet’ within that zone, as for ‘Surface liquid water zone’ would also example in Principium , issue one, page six. Further, the focus on habitable zones convey the intended meaning with vastly completely ignores any possibility of life more precision than at present. The obvious implication of the being based on anything other than adjective ‘habitable’ is that on such a Such terms would allow one to draw carbon chemistry with water as a solvent. planet or within such a zone, life may be the parallel with our own planet, while Such unconventional life may exist, or it found; outside such a zone, life may not leaving open the possibilities that may not; it is much too early to close our be found. This is quite clear, and also carbon-based, water-solvent, surface- eyes to the possibility. The book Evolving highly misleading. dwelling, non-technological life may not the Alien [a.k.a What Does a Martian look be the only type of life that may be At the present state of scientific Like?: The Science of Extraterrestrial Life – encountered in our exploration of the knowledge, the limits on the possible Ed] by Jack Cohen and Ian Stewart (Ebury Galaxy in which we live. locations of living organisms are simply Press, 2002) contains a lively exploration not known. It may in fact be the case of some mind-bending alternatives to life Stephen Ashworth that the life which has evolved in the as we know it, while stating, “the Researcher, I4IS Universe so far only occurs on and near astrobiological concept of a habitable zone the surfaces of Earth-analogue planets is largely useless,” (page 10). Principium welcomes letters and that have Earth-analogue orbits around Leading researchers such as Seth dialogue from our readers on all Sun-like stars. In such a case, the current Shostak and Paul Davies have argued in interstellar related topics. use of the term ‘habitable’ would indeed their recent publications that life at our be justified. But it may also be the case E-mail us at [email protected] . stage of development naturally goes on that life, even life as we know it, is found to produce civilisations consisting purely Please provide your full name with any in underground environments on any of autonomous computerised machinery. correspondence. The Editor reserves world with sub-surface liquid water. Regardless of one’s views as to whether the right to edit or shorten letters. We thus have the ironic situation that while interstellar researchers focus their attention on the supposed habitable Have Your Say zones around nearby stars, Solar System Join in the conversation by following the I4IS on our Facebook page researchers are getting excited about the http://www.facebook.com/InterstellarInstitute possibility of finding subterranean life on worlds such as Europa, Enceladus or You can also become part of our network on LinkedIn Titan, worlds which orbit well outside http://www.linkedin.com/groups?home&gid=4640147&trk=anet_ug_hm . that supposed zone in our own planetary Also check out the I4IS’ blog, the Interstellar Index, system. Obviously, if bodies such as these for more discussion and comments! are habitable to living organisms, then the zone of habitability is essentially http://www.interstellarindex.com/blog/ coextensive with the entire astronomical Follow Kelvin F Long and the I4IS on Twitter at Universe. A terrestrial-type world, https://twitter.com/thestarshipman generating internal heat for billions of

Principium | Issue 2 | January 2013 Page 5 Meet the Neighbours

Before deciding where to send current lack of data on very low mass degrees Celsius and is most unlikely to be planets, it could easily be many more. habitable. However, the presence of one an interstellar space probe it However, as things currently stand only planet implies that others may exist in the four of these stars are actually known to system and, given that alpha Centauri is will be necessary to perform a have planets. These are alpha Centauri B the closest possible target for an detailed inventory of the (a member of the alpha Centauri triple interstellar probe, it is very important to system at a distance of 4.4 light-years, and determine whether other planets are nearest stars to the Sun and thus one of the very closest stars to the indeed present. Although alpha Centauri Sun); epsilon Eridani (a single K-type star is a multiple star system, dynamical characterise, to the best extent at a distance of 10.5 light years), tau Ceti calculations indicate that planets should that we can, any planetary (a G-type star spectrally similar to the have stable orbits within about two Sun, 11.9 light years away and home to astronomical units of both alpha Centauri systems they may have, writes five planetary candidates – see the A and B, so habitable planets in the Ian Crawford. Advances section this issue for more) and system are certainly possible in principle. the red dwarf GJ 674 at a distance of 14.8 light years. As noted above, the statistics Cataloguing nearby star systems is going imply that many more stars within 15 light to be crucial for maximising both the years of the Sun will have planets, but they scientific returns and the design of such are currently below the detection a mission . Clearly we would wish to send thresholds of existing search methods. our first interstellar probe to a An excellent summary of all known scientifically interesting target but the extra-solar planets (currently more than more distant the target the longer the 850) can be found in the Extrasolar Planet mission will take, the greater the Encyclopedia maintained by Jean challenges to be faced by the hardware Schneider at the Paris Observatory. and software on board will be, and the higher the risk of damage by collision with interstellar dust particles. It follows that the designers of the probe will need to know the destination well in advance. Given realistic propulsion options it The Dog Star Sirius, which is the seems likely that the maximum range of brightest star in the sky, is a double star humanity’s first interstellar mission would with a white dwarf partner (nicknamed be of the order of 15 light years. This ‘the Pup’) both located 8.6 light years would imply a journey time of 150 years at from the Sun. However no planets have 10 percent of the speed of light – a hugely yet been found in the Sirius system. challenging undertaking but certainly not Image: NASA/ESA/H Bond (STScI)/M physically impossible. If we wanted Barstow (University of Leicester). journey times of the order of a human lifetime then, almost certainly, we would be restricted to targets within just a few Imaging our near neighbours light years. Within 15 light years of the Sun there are approximately 58 stars in 38 Unfortunately finding them will not be separate stellar systems. Probably the easy. The radial velocity technique used to most authoritative recent compilation, discover the alpha Centauri B planet was and the one on which my number of 58 Alpha Centauri – the closest star system really pushed to its limit for this discovery stars is based, is that published by the to the Solar System. A triple star, one of and finding an Earth-mass planet in an Research Consortium on Nearby Stars . its members hosts a planet. Earth-like (1 AU) orbit using the same Image: ESO/Digitised Sky Survey II. technique is at present impossible because Closest exoplanets the radial velocity signature decreases Owing to its relative proximity, the with increasing orbital distance. The Based on the detection rate of extra- planet orbiting alpha Centauri B prospects are not much better for the solar planets to date and allowing for the (provided the recently reported detection transiting technique that has recently known biases in the detection methods, it is confirmed by further work) is of been employed by the Kepler spacecraft to has been estimated that at least 30 particular interest from the point-of-view identify large numbers of planet percent of main sequence (i.e. Sun-like of planning interstellar space missions. candidates: the probability that an Earth- stars) stars will have planets of one sort or This planet has approximately the same sized planet in an Earth-like orbit around another (see Astronomical Considerations mass as Earth but is in a very tight (0.04 either alpha Centauri A or B will undergo Relating to the Choice of Target Star ). astronomical units, AU) orbit about the transits as seen from Earth is only about Thus, we might expect at least 17 of the star. At this orbital distance the planet’s one percent. It therefore seems likely that 58 stars within 15 light years to be daytime hemisphere will have a surface direct imaging, probably with large space accompanied by planets and, given the temperature well in excess of 1,000 telescopes specially designed to detect the

Principium | Issue 2 | January 2013 Page 6 An artist’s impression of the planetary system, including an asteroid belt, around the star epsilon Eridani, 10.5 light years away. Image: NASA/JPL–Caltech/T Pyle (SSC). faint light from planets orbiting nearby the Sun. Not only will these instruments stars, will be the most efficient means of be able to identify which stars have Jargon Buster characterising planets around alpha planets and calculate their orbital Centauri and other nearby stars. Direct parameters, they will be able to make imaging has the great advantage that, basic spectroscopic searches for Astronomical Unit having obtained the light from an extra- biosignatures in their atmospheres. Thus, An astronomical unit (AU) is the solar planet, it will be possible to analyse it although we currently cannot identify an average distance between Earth and spectroscopically to search for biomarker obvious specific target for humanity’s first the Sun, which is 149.6 million molecules in its atmosphere. interstellar space probe, when the time kilometres. This unit of measurement comes to build one we are likely to have a Although it may be possible to make a is used as the standard distance scale very good idea where to send it! start with currently planned instruments, for planetary systems, while light such as the 6.5-metre James Webb Space years are used for distances between Telescope to really make progress in the one star and another. There are characterisation of nearby planetary About the author 63,338 astronomical units in a light year. Our most distant probes, systems will probably require a dedicated Ian Crawford is Professor of Planetary infrared space interferometer such as the Voyager 1 and 2 (see our retrospective Science and Astrobiology at Birkbeck this issue) are by comparison only a European Space Agency’s proposed College, University of London Darwin mission. Although ESA has mere 122 and 100 AU from the Sun (http://www.bbk.ac.uk/es/staff/Ian_Crawford ), after 36 years of travel. decided not to proceed with the Darwin is Lead Designer for the Project Icarus study at the present time, something like ‘Astronomical Target’ module and is a this ambitious space-based instrument will member of the I4IS Advisory Council. almost certainly be required if we are ever to characterise nearby planetary systems in sufficient detail to plan interstellar missions to visit them. Fortunately, it seems likely that that the recent discovery of the alpha Centauri B planet will stimulate thinking along these lines. The bottom line is that only further observational work will reveal how common planets actually are around the nearest stars and what those planets are like. The good news is that, long before we will be in a position to build an interstellar spacecraft, astronomical technology will have reached the point where we will probably have a complete census of planetary systems within 15 light years of

Principium | Issue 2 | January 2013 Page 7 Retrospective: Voyager

NASA’s veteran Voyager this time. Within the next decade they are past the first two planets. Unfortunately expected to cross the boundary between little Pluto would miss out, although this probes have been true where the Sun’s magnetic influence ends has since been rectified by NASA’s New and that of interstellar space begins. Horizons probe, scheduled to encounter pioneers, from exploring the When that happens, the Voyagers will the diminutive dwarf planet in 2015. outer planets to becoming the become our first interstellar craft. first to venture to the edge Their story begins almost five decades ago, in 1960s California. Amidst the of the heliosphere. Here is decade of hippies, free love and war protests, at Pasadena’s Jet Propulsion their story. Laboratory an aerospace engineer by the name of Gary Flandro noted that the outer planets were aligned in such a way that by making use of gravitational assists – effectively using the gravity well of a planet as a slingshot to speed up a spacecraft and alter its trajectory – pairs of probes could be sent to all of the outer planets, including Pluto. It was going to be a once in a lifetime opportunity: the alignment neatly set The ringed world Saturn photographed itself up during the late 1970s and by Voyager 2. The two dots below are wouldn’t happen again for another 175 the moons Rhea and Dione. years. That the Space Age had dawned when it did was fortuitous indeed. It wasn’t to be. Ambition on this scale Braving the radiation belts Our interstellar adventure has already costs money and, with the United States The Voyagers launched weeks apart in begun, blasting off 36 years ago with the embroiled in a war in Vietnam, Congress August and September 1977 (Voyager 2 launch of twin science probes on missions simply wasn’t willing to part with the actually launched first, on 20 August, but of discovery. They were the Voyagers, billions of dollars that such a ‘Grand Tour’ was quickly overtaken by its sibling). spindly sets of booms and arms arranged would have gobbled up. So the programme Designed to function for at least five years, under the iconic shapes of their antenna was scaled back to just two robotic probes, their most severe test would be to navigate dishes, which toured the outer Solar namely Voyager 1 and 2, which would both the harsh radiation belts of Jupiter, which System and now venture boldly towards fly past Jupiter and Saturn with the option could fry their circuitry and shut them interstellar space, still operating and to carry onwards to Uranus and Neptune – down. Voyager 1 was first to enter the conducting scientific operations after all should they survive the hazardous journey danger zone on 5 March 1979, flying within 277,500 kilometres of Jupiter’s cloud tops and making its main observations of the Jovian system over a short 48-hour period. Voyager 2 repeated the fly-by on 9 July 1979 and both emerged unscathed, discovering in the process volcanoes on Io, new rings around Jupiter, numerous tiny new satellites and producing astonishing imagery of the tumultuous atmospheric bands that encircle the planet and the giant maelstrom that is the Great Red Spot – the biggest storm in the Solar System, large enough to engulf the Earth several times over. Fly-bys of the beautiful ringed planet Jupiter imaged by Voyager 1, with moons Io (left) and Europa (right) in the foreground, Saturn followed in November 1980 and and the Great Red Spot looming behind them. All images: NASA/JPL–Caltech. August 1981, with equally wide-ranging

Principium | Issue 2 | January 2013 Page 8 discoveries, but here is where the fates of moving slightly slower at 56,000 the two spacecraft separated. Voyager 1, kilometres per hour after its two extra upon reaching Saturn first, was tasked planetary encounters, passed the with two important objectives at the termination shock in September 2007. ringed planet: one, to fly behind the rings Interestingly, both did so at different and analyse the particles that make up distances from the Sun (Voyager 1 crossed their gossamer framework and two, get a at 94 astronomical units, i.e. 94 times closer look at Saturn’s enigmatic moon further from the Sun than Earth, while Titan. But this meant Voyager 1 had to fly Voyager 2 crossed at 84 astronomical past Saturn in its equatorial plane, which units), showing that, despite its name, the was tilted with respect to the plane of the heliosphere is not a sphere centred on the Solar System and the other planets. This Sun, but an elongated, teardrop shape trajectory would take it up and out of the streamlined by resistance to the Solar Solar System – there would be no Grand System’s motion through the interstellar Tour for this spacecraft. medium and inflating and deflating on the solar wind. Voyager 2, on the other hand, would plough onwards, gaining a gravity assist Brilliant, azure blue Neptune – the last Since crossing the termination shock, from Saturn to speed it towards Uranus in planet on the Grand Tour. the Low Energy Charged Particle (LECP) January 1986 and Neptune in August instruments on both Voyagers have 1989. Prior to these encounters the ice the Solar System and snap a group shot of monitored the speed of the solar wind giants, as they are termed, had appeared all the distant planets, leading to the slowing gradually from 241,000 kilometres through telescopic eyepieces as little more famous Pale Blue Dot photograph of per hour to zilch. It doesn’t mean that the than pale blobs. Voyager 2 brought them Earth. The jaw-dropping vista hints at how solar wind has dissipated, however; to life, the bland turquoise features of extraterrestrial observers may view our Voyager scientists merely suspect it has Uranus and its menagerie of odd moons planet from faraway. ‘turned a corner’ and the charged (especially patchwork-quilt Miranda) and particles of the solar wind – electrons, dim rings, and the azure blue of Neptune Interstellar component protons, ions, that kind of thing – riding with its white atmospheric ‘scooters’, the along the chaotic magnetic field lines in antithesis of Jupiter’s Great Red Spot in As Voyager 2 slid away into the the heliosheath have simply begun the form of a Great Dark Spot, plus more darkness, it was only the end of the moving perpendicular to the Voyager’s new moons and a close look at Triton and beginning. Now Voyager scientists direction of travel. its towering eight-kilometre high geysers scrambled into a new mode of exploration There have been more dramatic of nitrogen gas laced with black dust. – an interstellar mission, one that was to be shared by both Voyager craft on their occurrences recently. An increase in high- And then the Grand Tour was over, with separate trajectories out of the Solar energy cosmic rays coming in from beyond Voyager 2 likely to remain the only visitor System. Out there, in those deep, icy the Solar System over the past few years to the ice giants until at least the mid realms, the Sun still wields influence, even was to be expected. What wasn’t expected twenty-first century, even in the best case at a distance of 18 billion kilometres from was a sudden five percent increase in scenario. In 1990 Carl Sagan requested the Solar System’s warm heart. The cosmic rays detected by the LECP on 14 that Voyager 2 be turned to look back at further the Voyagers push into space, May 2012. A similar increase followed on however, the weaker that influence 28 July but this time it was accompanied becomes until one day they will reach the by a five-fold decrease in the number of point where the Sun reigns no longer and lower energy particles originating from the spacecraft will find themselves in the within the heliosphere. Then on 25 space between the stars. August Voyager 1 experienced the largest increase in cosmic rays yet, bringing the Think of the majority of the Solar total increase from March 2012 to 30 System – the planets, asteroids and the icy percent. Something strange was bodies of the Kuiper Belt – as being happening. encompassed within a giant magnetic bubble, blown on the supersonic gusts of Signposts the solar wind emanating from the Sun. This bubble is known as the heliosphere; We’ll know when the Voyagers pass the its outer boundary buffets against the signpost that states ‘you are now leaving magnetic fields of interstellar space, the heliosphere’, from which point on lies creating a turbulent region known as the interstellar space, when three key heliosheath on the inside of the boundary conditions are met. First is that the where the speed of the solar wind drops density of high-energy cosmic rays from below supersonic. Voyager 1, careening beyond the Solar System jumps up. through space at 61,000 kilometres per Second is that the density of low energy hour, crossed this ‘termination shock’ in particles from the heliosphere drops off. December 2004, but it wasn’t a clean That’s two boxes ticked. Crucially, crossing. Since the solar wind is not however, the third and final criteria is steady, but varies in response to solar that the magnetic field will suddenly activity, the termination shock moves change direction as the interstellar field During its fly-by of Uranus in January takes over. 1986 Voyager 2 imaged its odd moon inwards and outwards on the gusts of the Miranda with its chaotic terrain. solar wind like the ebb and flow of a tide “Had we been looking at the particle washing up on a distant shore. Voyager 2, data alone, we would have said we’re out,

Principium | Issue 2 | January 2013 Page 9 A diagram showing the different parts of the heliosphere, including the termination shock, heliosheath and bow shock, as well as the relative positions of the Voyager probes. out of the Solar System,” Stamatios boundary – and interstellar space beyond. time as the light delay will allow) only Krimigis of Johns Hopkins University, who Yet Ed Stone, Voyager’s Project Scientist when commanded to do so at times when is LECP’s lead scientist, told a NASA at JPL who has been with the mission the Deep Space Network (DSN) of radio press conference in December 2012. Yet since the very beginning, reckons it may dishes across the globe is pointed towards the onboard magnetometer indicated no be another five years before Voyager 1 it. Nothing is stored onboard the change in the magnetic field direction – marks that major milestone and becomes spacecraft. Given that the DSN is a Voyager was still within the heliosphere. humanity’s first ever interstellar emissary, shared resource, being utilised for swiftly followed by Voyager 2. Still, that’s communicating with the likes of probes at Instead, it is believed that Voyager 1, not bad for a pair of spacecraft that, on 13 Mars, Dawn in the Asteroid Belt, Juno on which is currently around 18 billion August 2012, became the longest the way to Jupiter, Cassini, New Horizons kilometres away (Voyager 2 lags behind, operating mission, surpassing Pioneer 6’s as well as the twin Voyagers, then 15 billion kilometres from the Sun), has record of 12,758 days. opportunities for communication are now hit the fast lane along a magnetic limited. highway that is driving low-energy Long-duration missions are a good particles out of the Solar System and habit to get into if one wishes to truly go Each Voyager is energised by a trio of allowing cosmic rays to race in. It is interstellar one day – even under the most radioisotope thermoelectric generators completely unexpected. “It’s as though powerful engines that we can realistically (RTGs), which produce power from the somebody opened the floodgates and the think of, it will still take decades to reach radioactive decay of plutonium-238. With water all moved downriver,” says Krimigis. the nearest star. Thus the Voyagers are a half-life of 87 years we know that the true pathfinders in this regard. That they plutonium power sources will decrease in This is likely the last, unexplored layer still produce useful science is a testament output to the point that in 2020 scientists of the heliosheath before Voyager 1 to the skill and quality that went into will have to begin switching instruments reaches the heliopause – that their construction. off and, by 2025, there won’t be enough aforementioned signpost at the outer energy for the spacecraft to function. The “[Voyager’s] instruments still do a Voyager mission will be at an end. remarkable job of returning high quality science data after over 35 years of space An interstellar journey travel,” says Arik Posner, the Voyager Program Scientist for NASA’s Heliospheric Suppose, however, the Voyagers were Division. Yet 1970s technology does have able to continue and, just suppose, they its limitations, he tells Principium . were able to reach another star. Can we “Voyager’s main limitation that could be take what we have learned from the improved with today’s technology is Voyagers about the interface between onboard data storage.” the heliosphere and interstellar space and apply it to what a future interstellar Voyager 1 is now in a new region of Remember, it is only relatively recently probe could expect to find upon entering the heliosheath, a magnetic highway that computer memory has become an ‘astrosphere’ around another star? that is allowing low-energy particles cheap; in the 1970s you were lucky to get a out of the heliosphere and high-energy few bits of data storage. Instead, Voyager We know that other stars traverse the cosmic rays in. relays everything that it observes and Galaxy embedded within their own measures in real time (or as much in real magnetic bubbles because we can see

Principium | Issue 2 | January 2013 Page 10 Infrared and Cosmic-ray subsystem ultraviolet Characterises the nature of cosmic rays and how they interact with both spectrometers the heliosphere and planetary These instruments magnetic fields and atmospheres. were designed to study planetary Photopolarimeter atmospheres. Mapped surface texture on planetary bodies and atmospheric composition Low Energy Charged by studying polarised light. Particle Instrument (LECP) By studying the energy of ions and electrons, the LECP is able to characterise the high-energy radiation environments of both planetary magnetic fields and the High gain antenna heliosheath. To communicate with Earth, receive commands and relay data

Optical calibration target and radiator

Electronics bus RTG Magnetometer Radioisotope This studied not only the Thermoelectric Generators magnetic fields of the gas Planetary radio and plasma used the radioactive decay giants but also how the solar wave antennae (2) of plutonium 238, wind interacts with those producing 470 watts of magnetic fields, and how the The plasma wave system studied the power at their peak. magnetic field interacts with the magnetic sheaths of the fields around the edge of the heliosphere and the giant planets as well as the plasma interstellar magnetic fields. properties of the heliosheath. them. Take Mira, for example, also Posner points out that the first data not going to be able to slow down, but known as omicron Ceti, the prototype to be gleaned upon approach to another rather whiz through any planetary for a class of variable red giant stars. star would be the conditions of the systems they come across. Voyager has This star is speeding through space, interstellar medium buffeting the prepared us for this kind of hasty ploughing through the diffuse gas of the astrosphere – in the case of Mira the science, squeezing out every last drop of interstellar medium. Like the white environment would be quite severe. science possible during fly-bys of the froth in the waves riding ahead of a boat, However, he points out that the Sun is outer planets that only lasted 48 hours. Mira’s astrosphere is also creating able to create a ‘neutral’ wind though Furthermore, as good as they have a bow shock in the interstellar medium, the exchange of charge between the been the Voyagers have taught us how leaving a long tail that in ultraviolet solar wind and the neutral interstellar we could do an interstellar mission light is reminiscent of a comet’s tail. gas. The resulting neutral wind, which better. “It is certainly clear that both This is a more extreme example, passes through magnetic fields like they energetic particle instruments and but many other stars have quieter are not there, could extend quite deep neutral atom imagers would be astrospheres much like the into the interstellar medium. emphasised [on a future mission],” says Sun’s heliosphere. “Therefore, approaching another star Ralph McNutt of the Johns Hopkins “Our knowledge about the more could allow us to analyse this neutral University Applied Physics Laboratory, benign astrospheres of stars that are stellar wind and infer properties of the who is co-investigator of Voyagers’ LECP similar in their interaction to ours is charged stellar wind before we would get and plasma science (PLS) instruments. rather limited due to the lack of immersed in it,” he says. This wind could McNutt should know; he was on the observational signatures,” says Posner. tell us about conditions deep within the science definition team for a NASA “Nonetheless, we will learn a lot from system, on the star itself. study of a dedicated mission to the stars, Voyager that will apply elsewhere as the Innovative Interstellar Explorer, in So how do the Voyagers stand as well and it is interesting to think the early 2000s. In addition, Arik Posner testbeds for a true interstellar mission of through a scenario of entering an proposes that an interstellar dust discovery? After reaching a significant astrosphere from the outside, whether detector would also be an advantage. percentage of the speed of light, a technically possible or not.” subsequent interstellar probe is probably

Principium | Issue 2 | January 2013 Page 11 symbol, a statement of humanity This record represents our hope and reaching out into space. Perhaps in the How gravity assists works determination and our goodwill in a future human interstellar explorers will vast and awesome Universe. chance upon the lost Voyager probes, the Despite being only tiny pebbles — President Carter greatest time capsules of all, showing compared to the vastness of the our ancestors a glimpse into a world that mighty, mythologically-tinged outer was, a world at the dawn of an planets, the Voyagers dared to steal Now into their thirty-sixth year, it interstellar future. from the gods. The alignment of the would be nice if the Voyagers could last planets that enabled the Grand Tour half a century. Alas, it seems they will wasn’t simply a case of permitting fall just short. When they do shut down, quicker travel times; it was an they’ll just be a light day from Earth, a far cry from the several light years to the essential necessity for the success nearest stars. They won’t truly be out of of the mission. the Solar System either. Although they Launched on Titan III/Centaur will have departed the heliosphere, the rockets, the Voyagers were only Sun’s gravity will still reign supreme in able to build up enough speed to the Oort Cloud of comets which is reach Jupiter – the Sun’s gravity well speculated to extend up to a light year would otherwise trap them in an away, possibly further. One day, however, elliptical orbit with aphelion out at the Voyagers will reach the stars. In the Jupiter’s orbit and perihelion near year 40,272, Voyager 1 will come within Earth’s orbit. The answer was a 1.7 light years of the star AC+79 3888 gravity assist off Jupiter itself. (also known as Gliese 445, the star is currently 17.6 light years away but Gravity assists, first developed in 1961 by JPL engineer Michael within forty millennia will have moved The cover to the golden disc carried much closer to us). Around the same Minovich, work on the basis of onboard both Voyager spacecraft momentum. As each of the time, Voyager 1 will fly within 1.7 light includes information on where to find years of the red dwarf star Ross 248 in Earth relative to local pulsars (bottom Voyagers plunged into Jupiter’s the constellation of Andromeda. left) and how to play the record (top gravity well, they were carried along left and right). At bottom right is a by the planet’s angular momentum. Epilogue depiction of a hydrogen molecule. Because they have mass, the Voyagers were able to transfer some In that far distant future, any intelligent being that stumbles across either of the of Jupiter’s angular momentum to Voyagers will find a gift attached to the themselves – in essence stealing it, spacecraft. A golden disc – a gold-plated providing a boost out of Jupiter’s copper phonographic record – containing gravity well and on towards Saturn. sounds and pictures from Earth and of At Saturn Voyager 2 pulled off the humans, including greetings in 55 same manoeuvre, as it also did at languages, classical music and Chuck Uranus. Despite the theft, the Berry’s Johnny B Goode. As the disc’s amount of angular momentum that recorded message from President Jimmy is ‘stolen’ is so miniscule as to not Carter says, “This record represents our be noticed by Jupiter, but to the hope and determination and our Voyagers it was a big deal, enough goodwill in a vast and awesome Further reading to take them into the icy, outer Universe.” The hopeful intention of the Voyager Interstellar Mission: depths of the Solar System and disc’s originators, including Carl Sagan, http://voyager.jpl.nasa.gov/ ultimately beyond. Jon Lomberg, Frank Drake, Timothy Ferris, Linda Salzman and Ann Druyan, Follow the Voyager probes on Twitter: was that any intelligent extraterrestrials https://twitter.com/NASAVoyager that found the Voyager probes could Contents of the golden records: learn of its origins, but in the vastness of http://en.wikipedia.org/wiki/Contents space such an encounter would be _of_the_Voyager_Golden_Record unlikely. Rather the golden records are a Where are the Voyagers? http://voyager.jpl.nasa.gov/where /index.html Michael Minovich’s gravity assist website: http://www.gravityassist.com/

Principium | Issue 2 | January 2013 Page 12 Reviews Hull Zero Three manages to integrate genetic seed banks, shattered by a living nightmare as the sleeper ships, the necessity for a moral main character stumbles about a cold, conscience in the face of contact with dark ship with only intermittent gravity Author: Greg Bear alien life and the possibility that an and no answers to his many questions. interstellar mission will be subsequently Bear permeates the opening 100 pages overtaken by missions with more with an atmosphere of terror that almost sophisticated technology (what Marc drips from the page as horrific monsters Millis describes as the ‘incessant stalk the ship’s empty corridors, but obsolescence postulate’). nothing really develops for those first 100 pages. Thankfully the chapters are Notable for interstellar enthusiasts is reasonably short, which helps the first the design of the ship, which is definitely half of the book pass quicker than it more hard SF than ‘sci-fi’. As the title otherwise would. As more survivors on indicates, there are three hulls – long, the ship are encountered, the mystery cylindrical structures each 12 kilometres begins to unfold and, given that for most long – atop pylons that attach to a of the bleak tale the character’s situation central icy comet taken from the Oort seems hopeless, the ending is filled with Cloud. Water is mined from this comet two quintessential ingredients of good to be used as a reaction mass for a SF: hope and wonder. Recommended, but fusion-based engine that drives the ship you have to be patient with it to get the at 20 percent of the speed of light. The rewards at the end. A staple of science fiction is the alien illusion of gravity is provided by the hulls invasion that aims to wipe human life rotating. One neat scene comes when the deflection shield that protects the hulls from Earth so that the aliens can claim Hull Zero Three our world as their own. But what if the is turned off by what the main characters boot were on the other foot? believe to be their unseen foe, and Hull Author: Greg Bear Zero Three becomes in danger of being Published by Gollancz (paperback, 307pp) This science fiction novel from Hugo scraped off the ship as it rams into Award winner Greg Bear takes our ideas interstellar detritus at 0.2c. ISBN: 978-0-575-10096-1 of interstellar colonisation and turns them on their head. It is a subtle read What about the story? The novel Find this book on Amazon via our but, without giving too much away, it begins when a dream of hope is Interstellar Index website .

Pandorum Like Hull Zero Three , the film begins hypersleep is not a new concept, it is with the main character, Corporal Bower an area of real ongoing medical research Dennis Quaid, Ben Foster (Foster) awaking from hibernation, and something we’ll explore more in an confused and alone, with wires and tubes upcoming issue. Meanwhile, the idea embedded in his ooze-covered skin. of ‘space madness’, while completely Slowly Bower begins to unravel the fictional, is driven by underlying mystery of the ship along with a psychological issues that may or may crewmate, Payton (Quaid) and assorted not go hand-in-hand with such deep other survivors he finds scattered space voyages. around the ship, while avoiding bouts Overall Pandorum is an interesting of space madness (‘pandorum’) and the film that, despite being somewhat cannibal-like creatures that threaten derivative, does have a neat twist to the everybody onboard. eventual outcome of their voyage and The workings of the ship are not as does attempt to bring the cinematic detailed or realistic as we might expect depiction of interstellar travel a little from a novel, but there are still some closer to what it may be in reality. concepts worth discussing. Bower has to stabilise the ship’s reactor; it is not said what type of reactor it is, but we Pandorum can assume it’s fusion (despite not Starring: Dennis Quaid, Ben Foster looking anything like a fusion reactor). This 2009 science fiction movie bears The journey to Tanis is quoted in the Directed by: Christian Alvart striking resemblances to Greg Bear’s Hull film as taking 123 years, again implying Script by: Travis Malloy & Christian Alvart Zero Three . An interstellar voyage onboard sub-light speed propulsion a gothic-looking sleeper ship named Find this movie on Amazon via our More interesting is the concept of a Elysium is transporting colonists from a Interstellar Index website . dying Earth to the newly discovered world sleeper ship, wherein the journey takes of Tanis. However, something has gone so long that the crew are placed in very wrong with the mission. hibernation for the duration. Although

Principium | Issue 2 | January 2013 Page 13 Planetary nebula NGC 5189. Image: We'd love to hear from you, our readers, NASA/ESA/Hubble Heritage Team about your thoughts on Principium, the R IN (STScI/AURA). Institute or interstellar flight in general. O T F E R E S Join us on our Facebook page to join in T T U

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