Centauri Dreams
Imagining and Planning Interstellar Exploration
To Ride the Solar Wind
What we hope to learn from early experiments with the electric sail is whether keeping a steady electric potential on long tethers will give us enough interaction with the solar wind to make for viable propulsion. ESTCube-1, launched earlier this week, is a step in that direction. Even though it uses but a single 10-meter wire, its rotation rate should change once the tether is fully extended and powered up. Bear in mind that ESTCube-1 is deep within the Earth’s magnetosphere, so the charged particles it will be interacting with are not from the solar wind, but a proof of principle is sought here that could make electric sailing a candidate for outer system-bound spacecraft.
It’s important to distinguish between solar sails and their electric counterparts. The Japanese IKAROS sail, successfully tested, showed that solar photons could impart momentum to a thin sail, as our experience with early satellites had already demonstrated. The beauty of sailing in any form is that we leave the propellant behind. The biggest problem with the rocket equation is that it tells us that as speed increases linearly, propellant mass increases exponentially. That’s why chemical rockets can’t take us to the stars, and why finding a way around carrying propellant has inspired concepts from lightsails to ramscoops and forms of pellet propulsion.
Pekka Janhunen’s work suggests that a fully developed electric sail might deploy 100 tethers by using its rotational motion, while an electron gun with beam sent along the spin axis would power up the system. In a sense, then, the electric sail does use electric power as part of producing thrust — in this way it’s similar to an ion engine. And in the sense that it hitches a ride on the solar wind, it could also be compared to the magnetic sail, which grew out of work by Dana Andrews and Robert Zubrin on creating a magnetic scoop to collect interstellar hydrogen. The magnetic scoop turned out to create more drag than the engine it fed could overcome, at which point the idea of using a magnetic sail for deceleration came into the picture.
An electric sail rides the solar wind using different principles, depending upon Coulomb interaction — the attraction or repulsion of particles caused by the electric charge — with the solar wind to get the work done. Positively charged solar wind protons are repelled by the positive voltage they encounter in the charged tethers. At the same time, captured electrons are ejected by an onboard electron emitter to avoid neutralizing the charge built up in the tether system.
Image: A full-scale electric sail consists of a number (50-100) of long (e.g., 20 km), thin (e.g., 25 microns) conducting tethers (wires). The spacecraft contains a solar-powered electron gun (typical power a few hundred watts) which is used to keep the spacecraft and the wires in a high (typically 20 kV) positive potential. The electric field of the wires extends a few tens of metres into the surrounding solar wind plasma. Therefore the solar wind ions “see” the wires as rather thick, about 100 m wide obstacles. A technical concept exists for deploying (opening) the wires in a relatively simple way and guiding or “flying” the resulting spacecraft electrically. Credit: Pekka Janhunen.
What worries some scientists about schemes that use the solar wind, though, is its variability. We’re dealing with a continuous stream of plasma flowing outward from the Sun. While a solar sail works with a steady source of photons, an electric sail will have to contend with solar wind particles that can vary between 400 and 800 kilometers per second. In their book Solar Sails: A Novel Approach to Interplanetary Travel, Gregory Matloff, Les Johnson and Giovanni Vulpetti compared riding the solar wind to putting a message into a bottle at high tide and throwing it out to see whether the currents will take it to the right destination.
But here the electric sail design may have an edge on magnetic concepts, because the spacecraft may be able to control the electric field that surrounds it. Would this be sufficient to produce a controlled level of thrust despite a rapidly shifting solar wind flowing past the vehicle? The question is unanswered, which is why we need early experiments like ESTCube-1 and the upcoming Aalto-1 to tell us more. But as he is the authority on electric sails, it seems pertinent to quote Pekka Janhunen on the matter. He believes that the thrust can be controlled by adjusting the electron gun current or voltage. This is from a 2009 paper delivered at the Aosta interstellar conference in Italy:
…there are two mechanisms that efficiently damp the variations of the electric sail thrust even when the solar wind parameters (density and speed) vary a lot. The first mechanism is due to the fact that the electron sheath width has an inverse square root dependence on the solar wind electron density. Thus when the solar wind density drops, the thrust becomes lower because the dynamic pressure decreases, but the simultaneous increase of the effect sail area (sheath width) partly compensates for the decrease.
So in at least one sense we have the possibility of a self-correcting system. Janhunen goes on:
The second mechanism arises from the natural desire to run the electric sail electron gun with the maximum available power. When the solar wind electron density drops, so does the electron current gathered by the tethers, so that one may increase the tether voltage (electron gun voltage) without increasing the power consumption. Both mechanisms combined imply that if applying the strategy of running the electric sail with the maximum available power, the thrust depends only on power ? of the solar wind density.
Janhunen goes on to say that the navigability of the electric sail is “almost as good as that of any other propulsion system such as an ion engine.” His results so far have shown that variations in the thrust are much weaker than variations in the solar wind itself, and careful juggling of power margins should allow the craft to correct for the unevenness of the flow. All this, of course, needs to be tested out in space, and not just through small, preliminary satellites but larger deployments that build upon what we learn. It’s good to see with the launch of ESTCube-1 that this process has begun.
The paper is Janhunen, “Status report of the Electric Sail: a revolutionary near term propulsion technique in the solar system,” in Proceedings of the 6th IAA Symposium on Realistic Near-Term Advanced Scientific Space Missions: Missions to the outer solar system and beyond, G. Genta (ed.), Aosta, Italy, 6-9 July 2009, 49-54, 2009.
Enter the Electric Sail
Some years back at the Aosta interstellar conference I had the pleasure of being on a bus making its way at night through the Italian alps with Pekka Janhunen sitting immediately in front of me. Janhunen (Finnish Meteorological Institute) is the developer of the electric sail concept soon to be tested by the ESTCube-1 satellite, which launched last night aboard a Vega rocket from the Kourou spaceport in French Guiana. Our group had been talking about interstellar issues all day at the conference and now, headed back to the hotel following a memorable dinner at high elevation, I was curious whether an electric sail had interstellar applications.
The immediate answer seemed to be no, given that the highest velocities Janhunen had been talking about for the idea were about 100 kilometers per second, much faster than Voyager 1’s 17 kilometers per second, but a long way short of what we would like to see on an interstellar flight. But the ever thoughtful Pekka pointed out to me that as a means of deceleration, electric sails might have a future, braking against the stellar wind from a destination star. Deceleration being a huge problem for any interstellar probe, the idea has stuck with me ever since.
Image: The electric sail is a space propulsion concept that uses the momentum of the solar wind to produce thrust. Credit: Alexandre Szames.
What an electric sail would do is to ride the stream of charged particles flowing out from the Sun, and fast missions to the outer system could thus be implemented if we get the system into full gear. The ESTCube-1 satellite, the work of Estonian students testing out Janhunen’s ideas, uses a long wire that maintains a steady electric potential as its means of interacting with the solar wind. Janhunen, in an article in IEEE Spectrum, calls ESTCube-1 “…the first attempted experiment to measure the Coulomb drag experienced by a charged wire or tether in moving plasma.”
ESTCube-1’s tether is a 50 micrometer wide, 10 meter long wire made out of four strands of aluminum that will gradually be deployed from the satellite in a process that could take as much as a week. Once deployed, the tether will be charged and variations in the satellite’s rotation rate will, if all goes well, reveal the interactions between it and atmospheric ions. But future electric sails will soon be deploying longer wires. A follow-up to ESTCube-1 called Aalto-1 is designed around a 100-meter tether. This one is also a student project, built at Aalto University in Finland and designed in part to test charged tethers as a means of deorbiting small satellites.
Assuming the concept passes its initial muster, we can look forward to upsized missions using tethers up to 20 kilometers long, deploying as many as a hundred of these from a single spacecraft. This is the design that, in computer simulations, yields potential speeds of 100 kilometers per second, fast enough to get a payload into the nearby interstellar medium in about fifteen years. With a spacecraft like this, keeping the sail’s wires in a 20 kV positive potential allows the sail to ride the solar wind ions while making issues of deployment relatively simple.
A sail like this is surprisingly efficient. From a page on the concept maintained by Pekka Janhunen:
The solar wind dynamic pressure varies but is on average about 2 nPa at Earth distance from the Sun. This is about 5000 times weaker than the solar radiation pressure. Due to the very large effective area and very low weight per unit length of a thin metal wire, the electric sail is still efficient, however. A 20-km long electric sail wire weighs only a few hundred grams and fits in a small reel, but when opened in space and connected to the spacecraft’s electron gun, it can produce several square kilometre effective solar wind sail area which is capable of extracting about 10 millinewton force from the solar wind.
As with any sail, the effect is small but cumulative and yields serious velocities over time:
…by equipping a 1000 kg spacecraft with 100 such wires, one may produce acceleration of about 1 mm/s2. After acting for one year, this acceleration would produce a significant final speed of 30 km/s. Smaller payloads could be moved quite fast in space using the electric sail, a Pluto flyby could occur in less than five years, for example. Alternatively, one might choose to move medium size payloads at ordinary 5-10 km/s speed, but with lowered propulsion costs because the mass that has to launched from Earth is small in the electric sail.
ESTCube-1 will help us measure the forces exerted on its single tether by the ionospheric ram flow acting on the satellite, a flow that substitutes for the solar wind in the case of this small CubeSat mission. The Aalto-1 test will occur next year if all goes well, and we will then have to see how the electric sail stands up compared to its solar sail competition. More on electric sail concepts tomorrow, when I want to look at important questions of stability.
A key paper on electric sails is Janhunen and Sandroos, “Simulation study of solar wind push on a charged wire: solar wind electric sail propulsion,” Annales Geophysicae 25, (2007), pp. 755-767.
Update on Starship Century Symposium
We had a successful launch last night of the ESTCube-1 satellite from Kourou, about which more tomorrow when I’ll be talking about electric sails and their uses both interplanetary and interstellar. But this morning, with the Starship Century Symposium rapidly approaching, I wanted to run this overview, which corrects and updates several things in the post I published a couple of weeks ago. Seats are still available for those of you in range. Thanks to Jim Benford for the following:
The Starship Century Symposium is the inaugural event at the new Arthur C. Clarke Center for Human Imagination at UC San Diego, Tuesday Wednesday, May 21-22. The program is located here. The symposium celebrates the publication of the Benfords’ anthology, Starship Century. Jon Lomberg, the artist who collaborated extensively with Carl Sagan, has read the book and has this comment:
Starship Century is the definitive document of this moment in humanity’s long climb to the stars. Here you can find the physics, the astronomy, the engineering, and the vision that provides the surest guideposts to our future and destiny.
A number of luminaries will discuss a wide variety of starship-related topics derived from the book. The gathering features thinkers from a variety of disciplines including scientists, futurists, space advocates and science fiction writers. The program includes Freeman Dyson, Paul Davies, Robert Zubrin, Peter Schwartz, Geoffrey Landis, Ian Crawford, James Benford and John Cramer. Science fiction writers included are Neal Stephenson, Gregory Benford, Allen Steele, Joe Haldeman and David Brin. Other writers attending are Jerry Pournelle, Larry Niven and Vernor Vinge.
The book will be available for sale for the first time on Tuesday the 21st at a book signing immediately following the first day of the Symposium. There many of the authors in the anthology will be available for signing. Following the first day of the Symposium there will be a reception featuring an exhibition of Arthur C. Clarke artifacts in the Giesel Library of UCSD.
In addition to the speakers, there are a number of panels. One, about the development of the Solar System, is ‘The Future of New Space’. Another is a panel on ‘Getting to the Target Stars,’ moderated by SETI celebrity Jill Tarter. The conclusion is a science fiction writers panel, ‘Envisioning the Starship Era,’ moderated by Gregory Benford and featuring Joe Haldeman, David Brin, Vernor Vinge and Jon Lomberg. At the conclusion of the Symposium there will be a book signing for other books of the authors present. There will also be a later book signing at Mysterious Galaxy bookstore a few miles from the University. It will feature Starship Century and the works of the other writers present.
The Symposium will be webcast and then archived. The webcast, which activates at the time of the event, is here.
The Benfords will donate the profits from sale of the book to interstellar research activities. They are currently working to establish a research committee that will award research contracts. The edition available at the symposium will be unique, a collectors item. The book will then go into general distribution in the summer. The Benfords recommend purchasing through a link that will soon appear on the Starship Century website.
This route is optimal because it maximizes the percentage profit, thus maximizing the money available for research. As we all know, research dollars have been greatly lacking in the interstellar area, which is one reason why the interstellar organizations such as Icarus Interstellar, Tau Zero and the Institute for Interstellar Studies are volunteer organizations. The Benfords are planning a second symposium to be held in London in the fall.
Robert Goddard’s Interstellar Migration
Astronautics pioneer Robert H. Goddard is usually thought of in connection with liquid fuel rockets. It was his test flight of such a rocket in March of 1926 that demonstrated a principle he had been working on since patenting two concepts for future engines, one a liquid fuel design, the other a staged rocket using solid fuels. “A Method of Reaching Extreme Altitudes,” published in 1920, was a treatise published by the Smithsonian that developed the mathematics behind rocket flight, a report that discussed the possibility of a rocket reaching the Moon.
While Goddard’s work could be said to have anticipated many technologies subsequently developed by later engineers, the man was not without a visionary streak that went well beyond the near-term, expressing itself on at least one occasion on the subject of interstellar flight. Written in January of 1918, “The Ultimate Migration” was not a scientific paper but merely a set of notes, one that Goddard carefully tucked away from view, as seen in this excerpt from his later document “Material for an Autobiography” (1927):
“A manuscript I wrote on January 14, 1918 … and deposited in a friend’s safe … speculated as to the last migration of the human race, as consisting of a number of expeditions sent out into the regions of thickly distributed stars, taking in a condensed form all the knowledge of the race, using either atomic energy or hydrogen, oxygen and solar energy… [It] was contained in an inner envelope which suggested that the writing inside should be read only by an optimist.”
Optimism is, of course, standard currency in these pages, so it seems natural to reconsider Goddard’s ideas here. As to his caution, we might remember that the idea of a lunar mission discussed in “A Method of Reaching Extreme Altitudes” not long after would bring him ridicule from some elements in the press, who lectured him on the infeasibility of a rocket engine functioning in space without air to push against. It was Goddard, of course, who was right, but he was ever a cautious man, and his dislike of the press was, I suspect, not so much born out of this incident but simply confirmed by it.
In the event, Goddard’s manuscript remained sealed and was not published until 1972. What I hadn’t realized was that Goddard, on the same day he wrote the original manuscript, also wrote a condensed version that David Baker recently published for the British Interplanetary Society. It’s an interesting distillation of the rocket scientist’s thoughts that speculates on how we might use an asteroid or a small moon as the vehicle for a journey to another star. The ideal propulsion method would, in Goddard’s view, be through the control of what he called ‘intra-atomic energy.’
Image: Rocket pioneer Robert H. Goddard, whose notes on an interstellar future discuss human migration to the stars.
Atomic propulsion would allow journeys to the stars lasting thousands of years with the passengers living inside a generation ship, one in which, he noted, “the characteristics and natures of the passengers might change, with the succeeding generations.” We’ve made the same speculation here, wondering whether a crew living and dying inside an artificial world wouldn’t so adapt to the environment that it would eventually choose not to live on a planetary surface, no matter what it found in the destination solar system.
And if atomic energy could not be harnessed? In that case, Goddard speculated that humans could be placed in what we today would think of as suspended animation, the crew awakened at intervals of 10,000 years for a passage to the nearest stars, and intervals of a million years for greater distances. Goddard speculates on how an accurate clock could be built to ensure awakening, which he thought would be necessary for human intervention to steer the spacecraft if it came to be off its course. Suspended animation would involve huge changes to the body:
…will it be possible to reduce the protoplasm in the human body to the granular state, so that it can withstand the intense cold of interstellar space? It would probably be necessary to dessicate the body, more or less, before this state could be produced. Awakening may have to be done very slowly. It might be necessary to have people evolve, through a number of generations, for this purpose.
As to destinations, Goddard saw the ideal as a star like the Sun or, interestingly, a binary system with two suns like ours — perhaps he was thinking of the Alpha Centauri stars here. But that was only the beginning, for Goddard thought in terms of migration, not just exploration. His notes tell us that expeditions should be sent to all parts of the Milky Way, wherever new stars are thickly clustered. Each expedition should include “…all the knowledge, literature, art (in a condensed form), and description of tools, appliances, and processes, in as condensed, light, and indestructible a form as possible, so that a new civilisation could begin where the old ended.”
The notes end with the thought that if neither of these scenarios develops, it might still be possible to spread our species to the stars by sending human protoplasm, “…this protoplasm being of such a nature as to produce human beings eventually, by evolution.” Given that Goddard locked his manuscript away, it could have had no influence on Konstantin Tsiolkovsky’s essay “The Future of Earth and Mankind,” which in 1928 speculated that humans might travel on millennial voyages to the stars aboard the future equivalent of a Noah’s Ark.
Interstellar voyages lasting thousands of years would become a familiar trope of science fiction in the ensuing decades, but it is interesting to see how, at the dawn of liquid fuel rocketry, rocket pioneers were already thinking ahead to far-future implications of the technology. Goddard was writing at a time when estimates of the Sun’s lifetime gave our species just millions of years before its demise — a cooling Sun was a reason for future migration. We would later learn the Sun’s lifetime was much longer, but the migration of humans to the stars would retain its fascination for those who contemplate not only worldships but much faster journeys.
Starship Musings: Warping to the Stars
by Kelvin F.Long
The executive director of the Institute for Interstellar Studies here gives us his thoughts on Star Trek and the designing of starships, with special reference to Enrico Fermi. Kelvin is also Chief Editor for the Journal of the British Interplanetary Society, whose latest conference is coming up. You’ll find a poster for the Philosophy of the Starship conference at the end of this post.
Like many, I have been inspired and thrilled by the stories of Star Trek. The creation of Gene Roddenberry was a wonderful contribution to our society and culture. I recently came across an old book in the shop window of a store and purchased it straight away. The book was titled The Making of Star Trek, The book on how to write for TV!, by Stephen E.Whitfield and Gene Roddenberry. It was published by Ballantine books in 1968 – the same year that the Stanley Kubrick and Arthur C Clarke 2001: A Space Odyssey came out. What with all this and Project Apollo happening, the late 1960s was a time to have witnessed history. Pity I wasn’t born until the early 1970s when the lunar program was winding down. I digress…
In this book, one finds the story of how Roddenberry tried to market his idea for a new type of television science fiction show. It is clear from reading it that Roddenberry was very much concerned for humankind and in the spirit of Clarke’s positive optimism, he was trying to steer us down a different path. In this book we find out many wonderful things about the origins of Star Trek, including that the U.S.S Enterprise was originally called the U.S.S Yorktown and that Captain James T.Kirk was originally Captain Robert T. April. He was described as being “mid-thirties, an unusually strong and colourful personality, the commander of the cruiser”.
The time period that Star Trek was said to be set was sometime between 1995 and 2995, close enough to our times for our continuing cast to be people like us, but far enough into the future for galaxy travel to be fully established. The Starship specifications were given as cruiser class, gross mass 190,000 tons, crew department 203 persons, propulsion drive space warp, range 18 years at light-year velocity, registry Earth United Spaceship. The nature of the mission was galactic exploration and investigation and the mission duration was around 5 years. Reading these words today, we see that what Roddenberry was doing was laying the foundations for many future visions of what starships would be like.
To Craft a Starship
What I found absolutely fascinating about reading this book however, was the process by which Roddenberry and team actually came up with the U.S.S Enterprise design. Roddenberry met with the art department and in the summer of 1964 the design of the starship was finalised. The art directors included Pato Guzman and Matt Jefferies. Roddenberry’s instructions to the team on how to design the U.S.S Enterprise were clear:
“We’re a hundred and fifty or maybe two hundred years from now. Out in deep space, on the equivalent of a cruise-size spaceship. We don’t know what the motive power is, but I don’t want to see any trails or fire. No streaks of smoke, no jet intakes, rocket exhaust, or anything like that. We’re not going to Mars, or any of that sort of limited thing. It will be like a deep-space exploration vessel, operating throughout our galaxy. We’ll be going to stars and planets that nobody has named yet”. He then got up and, as he started for the door, turned and said, “I don’t care how you do it, but make it look like it’s got power”.
According to Jefferies, the Enterprise design was arrived at by a process of elimination and the design even involved the sales department, production office and Harvey Lynn from the Rand Corporation. The various iterations produced many sheets of drawings – I wonder what happened to those treasures? The book shows some of the earlier concepts the team came up with.
Today, many in the general public take interstellar travel for granted, because Star Trek makes it look so easy with its warp drives and antimatter powered reactions. But for those of us who try to compute the problem of real starship design, we know the truth – that it is in fact extremely difficult. Whether you are sending a probe via fusion propulsion, laser driven sails or other means, the velocities, powers, energies are unreasonably high from the standpoint of today’s technology. But it is the dream of travelling to other stars through programs like Star Trek that keeps our candles burning late into the night as we calculate away at the problems. In time, I am sure we will prevail.
Fermi’s Enterprise?
There is an element of developing warp drive theory however that is usually neglected and I think it is now time to raise it – the implications to the Fermi Paradox. This is the calculation performed by the Italian physicist Enrico Fermi around 1950 that given the number of stars in the galaxy, their average distance, spectral type, age and how long it takes for a civilization to grow – intelligent extraterrestrials should be here by now, yet we don’t see any. Over the years there have been many proposed solutions to the Fermi paradox. In 2002 Stephen Webb published a collection of them in his book If the Universe is Teeming with Aliens…Where is Everybody? Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life, published by Paxis.
One of the ways to address this is to ask if interstellar travel was even feasible in theory, and as discussed in my recent Centauri Dreams post on the British Interplanetary Society, Project Daedalus proved that it was. If you can design on paper a machine like Daedalus at the outset of the space age, what could you do in two or three centuries from now?
But even then travel times across the galaxy would be quite slow. The average distance between stars is around 5 light years, the Milky Way is 1,000 light years thick and 100,000 light years in diameter. Travelling at around ten percent of the speed of light the transit times for these distances would be 50 years, 10,000 years and 1 million years respectively. These are still quite long journeys and the probability of encountering another intelligent species from one of the 100-400 billion stars in our galaxy may be low. But what if you have a warp drive?
The warp drive would permit arbitrarily large multiple equivalents of the speed of light to be surpassed, so that you could reach distances in the galaxy fairly quickly. Just like Project Daedalus had to address whether interstellar travel was feasible as an attack on the Fermi Paradox problem, so the warp drive is yet another question – are arbitrarily large speeds possible, exceeding even the speed of light?
If so, then our neighbourhood should be crowded by alien equivalents of the first Vulcan mission that landed on Earth in the Star Trek universe. To my mind, if we can show in the laboratory that warp drive is feasible in theory as a proof of principle, and yet we don’t discover intelligent species outside of the Earth’s biosphere, then of the many solutions to the Fermi paradox, perhaps there are only two remaining. The first would be some variation on the Zoo hypothesis, and the second is that we are indeed alone on this pale blue dot called Earth. Take your pick what sort of a Universe you would rather exist in.
Stars for JWST
Red dwarfs or brown? The question relates to finding targets as the James Webb Space Telescope gets closer to launch. We’re going to want to have a well defined target list so that the JWST can be put to work right away, and part of that effort means finding candidate planets the telescope can probe. Yesterday’s white paper on a proposed search for brown dwarfs using the Spitzer Space Telescope lined up a number of reasons why these objects are good choices:
* for a given planetary equilibrium temperature, the orbit gets shorter with decreasing primary mass, increasing the probability of transit and providing 50+ occultations per year (and 50+ transits);
* the planet to brown dwarf size ratio means transiting rocky planets produce deep transits and permit the detection of planets down to Mars’ size in a single transit event when using Spitzer;
* the reliability of the detection is helped by the absence of known false astrophysical positives: brown dwarfs have very peculiar colors, small sizes, and being nearby, have a high proper motion allowing to check what is within their glare
All this is in addition to the fact that the fainter the star, the greater the contrast between the primary and the planet. But interest in red dwarfs remains high as well. Here again we are dealing with small stars where the habitable zone can be closer than the distance between Mercury and the Sun, making for easier transit detections than with G or K-class stars. Daniel Angerhausen (Rensselaer Polytechnic Institute) and team are thus proposing a project of their own called HABEBEE, for “Exploring the Habitability of Eyeball Exo-Earths.”
Eyeball? This online feature in Astrobiology Magazine lays out the background. Angerhausen knows that tidal lock will set in on a closely orbiting planet, with the night side likely covered in ice while the day side could offer, at the right orbital distance, clement conditions for life. The article cites the disputed candidate planet Gliese 581g as a possible ‘eyeball’ world, but there seems to be little need to single out such a controversial object. Planets meeting this description should be relatively common given that M-dwarfs make up 70-80 percent of all stars in the galaxy, so that it’s possible they are the most abundant locations of life.
“A little bit closer to the star — that is, hotter — they would completely thaw and become waterworlds,” Angerhausen tells Astrobiology Magazine‘s Charles Choi; “[A] little bit further out in the habitable zone — that is, colder — they would become total iceballs just like Europa, but with a potential for life under the ice crust. These planets — water, eyeball or snowball — will most probably be the first habitable planets we will find and be able to characterize remotely. Thats why it is so important to study them now.”
Image: This artist’s impression shows a sunset seen from the super-Earth Gliese 667 Cc. The brightest star in the sky is the red dwarf Gliese 667 C, which is part of a triple star system. The other two more distant stars, Gliese 667 A and B appear in the sky also to the right. Finding planets in the habitable zones of red dwarfs and characterizing their atmospheres will be a major component in our search for life in the universe. Credit: ESO/L. Calçada.
There’s plenty to work with, especially given the flare situation on younger M-dwarfs, which can cause ultraviolet radiation spikes of up to 10,000 times normal levels. We have copious information about M-dwarf flares that has been gathered by observers over the years, while new observations of likely JWST candidate stars should help us characterize those more likely to host habitable planets. Radiation experiments involving the Brazilian National Synchrotron Light Source at Campinas will help the team understand the effects of radiation on ice.
The plan is to put together various models for red dwarf planets in the habitable zone that will help astronomers predict how well existing and future telescope surveys can find them. The team also hopes to travel to Antarctica to gather microbes in places that are transition zones between ice and water. They’ll use a planetary simulation chamber that was originally designed at the Brazilian Astrobiology Laboratory to mimic conditions on Mars. There the Antarctic microbes can be tested under various conditions of radiation and atmosphere to simulate M-dwarf possibilities.
So many unknowns, no matter what kind of star we home in on. I suspect that Amaury H.M.J. Triaud (Kavli Institute for Astrophysics & Space Research), who heads up the brown dwarf team, and Angerhausen himself would agree that we can’t be doctrinaire about where we look for life. Their proposals focus on brown or red dwarfs respectively not because they think these are the only possibilities for life, but because a case can be made that finding rocky worlds in the habitable zones of such stars will be quicker and the planets more easily characterized than the alternatives. The more we learn now, the better we’ll be able to use our future instruments.
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