by Paul Gilster | Jun 8, 2012 | Sail Concepts |
Thinking about the poem “To Sail Beyond the Sun: A Luminous Collage,” which I published excerpts from yesterday, I was reminded that if Ray Bradbury didn’t spend a lot of time on solar sails, many of his compatriots did. Indeed, the early story of the solar sail is inseparable from science fiction. Astounding Science Fiction‘s John Campbell published the first serious look at solar sails for propulsion all the way back in May of 1951. The article’s title, “Clipper Ships of Space,” would be echoed by a highly influential paper by Gregory Matloff and Eugene Mallove called “Solar Sail Starships: The Clipper Ships of the Galaxy,” which ran in the Journal of the British Interplanetary Society in 1981.
The thirty years that passed between publication of the two articles saw the solar sail come into its own as a serious mission concept. Carl Wiley, who wrote the essay in Astounding, knew that many scientists and engineers were science fiction readers, but he was concerned enough about his reputation to submit his thoughts under the byline ‘Russell Saunders.’ The idea had much deeper roots, to be sure. Both Konstantin Tsiolkovsky and Friderikh Arturovich Tsander had considered the benefits of thin reflectors in space and J.D. Bernal discussed space sails in The World, the Flesh & the Devil (1929). The notion of sailing even shows up in the writings of Johannes Kepler.
But Wiley got the idea out to an audience comprised of people with the skills to move it forward. In 1958, Richard Garwin produced the first treatment of solar sails in a technical journal called Jet Propulsion, and within just a few years science fiction went at the topic with gusto. Several writers come immediately to mind, the first being Cordwainer Smith (Paul Linebarger),whose moody fable “The Lady Who Sailed the Soul” ran in Galaxy in 1960. Jack Vance’s “Gateway to Strangeness” (Amazing Stories, August 1962) considered the training of a solar sail crew, the same year Robert Forward began writing about beamed propulsion in the journal Missiles and Rockets.
Arthur C. Clarke was an early sail advocate, publishing a story originally called “Sunjammer” in Boy’s Life in 1964. Confusingly, Poul Anderson (writing as ‘Winston P. Sanders’) followed up with a story under the same title in Analog about a month later. The Clarke title, obligingly re-titled “The Wind from the Sun,” remains a classic. Anderson’s “Sunjammer” and Clarke’s “The Wind from the Sun” are helpfully collected in the book I mentioned yesterday, Project Solar Sail, while the Smith story can be found in The Best of Cordwainer Smith, out of print but widely available in used bookstores or online, and the Vance is available in The Best of Jack Vance (1976). Ah, the pleasures of hunting down old books!
As to Project Solar Sail, it’s an indispensable title that should be on your shelf, likewise out of print but worth seeking out. Along with the fiction and poetry by Bradbury as well as Tennyson, you get Robert Forward on lightsails, and Louis Friedman on the interplanetary economy sails might one day make possible, not to mention Eric Drexler’s “The Canvas of the Night,” which looks at how sails might be built in space and deployed throughout the system.
Les Johnson gets into this same issue in Going Interstellar, his newly released collection of essays and fiction from Baen. Building a sail in space instead of launching it from Earth has many advantages. Launching a payload is hugely stressful — you can think of what the inside of a Space Shuttle looks like not long after liftoff — and sails are inherently delicate because the thinner we can make them, the lower the mass and the more effective the design. But even if the sail makes it to low Earth orbit, it must still be deployed. We can get past packaging and deployment issues with relatively small near-term sails, but as we look to a future of sails kilometers on a side, it’s clear that future manufacturing facilities in space would be the preferable option.
All this is easier said than done, of course, but maybe we don’t have to wait for a full factory infrastructure to be placed into Earth orbit to move ahead. Johnson’s thoughts:
There is another approach that takes advantage of the Earth’s well established manufacturing infrastructure and the unique environment of space to solve the manufacturing and launch problems: build the sail on Earth, but make it more robust — thicker — than the mission requires and make the extra thickness out of materials that won’t easily tear when in the Earth’s gravity and that will not damage easily during launch. But, design the more robust sail so that the heaviest part will separate when exposed to a selected portion of the Sun’s ultraviolet light — which only happens when we are above the Earth’s atmosphere. Voila! The thick and heavy sail that was easier to make and launch quickly becomes the wispy, lightweight sail needed for rapid propulsion through interstellar space.
In his “Canvas of the Night” essay, Drexler talks about getting away from sails with plastic backing and creating unbacked aluminum films a few hundred atoms thick. Using the right structural materials, he believes such a sail could be twenty to eighty times lighter than deployable plastic-film sails. But he’s not ready to give up the space manufacture of these sails, noting that learning to build such sails in space would hone our skills at working in this environment even as we built the propulsion systems that would take us deeper into the Solar System.
And what about the vast structures Robert Forward envisioned when he talked about beamed propulsion to a lightsail? A big enough laser could push a crewed starship to Alpha Centauri at 10 percent of lightspeed, but it’s hard to imagine human labor building the 1000-kilometer lens in the outer Solar System that Forward thought would be needed to collimate his huge laser beam. Here again I’m thinking about Drexler, for a future enriched by nanotechnology may offer a solution. No one knows when and if the promise of nanotech will truly arrive, but it’s not inconceivable that given enough time, we will be able to produce the kind of smart assemblers that could use nearby materials to construct large structures in space.
Meanwhile, the path forward is clear: Build ever larger and lighter sails. Experiment with beamed propulsion and consider different kinds of sail materials and interesting prospects like desorption, in which materials painted onto a sail can give it an extra boost (see A Boost for Solar Sails, in which James and Gregory Benford’s sail experiments are discussed). And be aware of the new ideas that the mixing of science with fiction can bring. It’s no surprise to me that a superb science fiction writer like Gregory Benford should be involved in sail studies, or that Arthur C. Clarke saw the promise of solar sailing long before actual sail experiments began.
And speaking of science fiction, read a little Bradbury this weekend. If you’re already familiar with his work, you have your own favorites. If not, I’d suggest either The Martian Chronicles or The Illustrated Man as the best entry points.
by Paul Gilster | Jun 7, 2012 | Culture and Society |
Thinking of Ray Bradbury, as I suppose most of us were yesterday after learning of his death, I found my reminiscences of his work mixing with what was to have been today’s topic, solar sails and their beamed sail counterparts. I’ve read almost all of Bradbury’s work up through the 1960s and admittedly little after that, but he’s a writer I return to often to try to recapture the early magic. I was going through his stories trying to think of one involving solar sails and I came up blank, but in a moment of pure serendipity, I realized that a book I mentioned yesterday held a little Bradbury gem that was all about sails and their implications for the human imagination.
The book is Arthur C. Clarke’s collection Project Solar Sail (Roc, 1990), which contains a poem Bradbury wrote with Jonathan V. Post called “To Sail Beyond the Sun: A Luminous Collage.” Like so much of Bradbury’s work, it uses language like witchcraft to pull you into the experience, and like so much of the later Bradbury, it’s a bit overwrought in places, yet when it hits the right note — and it does this more often than not — the poem weaves a kind of enchantment:
And so we earn what we shall dare
Tossed from the central sun
We with our own concentric fires
Blaze and burn
Burn and blaze. Until we feel
Once at the hub of wakening
the vast starwheel…
Of course, it’s hard to separate out what is Bradbury’s and what his co-author’s work, but the Bradbury lyricism is the dominant force, a deep music that goes back to his pulp magazine days. That music offers the rich counterpoint to The Martian Chronicles, themselves composed as short stories for the magazine market before being assembled into a coherent sequence. In places in this poem there is a taste of Gerard Manley Hopkins, and in both Hopkins and Bradbury an echo of the sturdy alliterative line that drove early Anglo-Saxon verse. You can hear that in places like this:
Small sparks, large sun —
All one, it is the same.
Large flame or small
as long as my heart is young
the flavor of the night lies on my tongue…
The Universe is thronged with fire and light,
And we but smaller suns which, skinned, trapped and kept
where we have dreamed, and laughed, and wept
Enshrined in blood and precious bones,
with heartbeat’s rhythms, passion’s tones
Hold back the night…
I came to Ray Bradbury through a 1955 collection called The October Country, a battered paperback copy of which I still have on my shelves. It was a challenging approach for a boy who had never encountered what a deft writer could do with the macabre — many of these tales were written for Weird Tales (they later appeared as part of a collection called Dark Carnival before finding their way into The October Country) and they pushed psychic buttons I didn’t know existed. I particularly recall “Skeleton,” a story about a man who develops a phobia about the bones inside his body, and “The Jar,” which caused me to put the book aside for a week before working up the nerve to see what could possibly follow it. I would have been about ten at the time.
Bradbury had a long career in the pulps, and somewhere in this office I have a copy of “Pendulum,” his first professionally published story, which appeared in Super Science Stories in November of 1941. Of course, he would soon move into the glossy magazines and win acclaim for the prescient and eerie fiction of The Illustrated Man (1951) and Fahrenheit 451 (1953) and soon he was a cultural icon, working for Hollywood, producing plays, poems and essays and always turning out his 1000 words a day, a practice he recommended in Zen and the Art of Writing (1990). I taught The Martian Chronicles a couple of times while working as a teaching assistant at a university and loved introducing new readers to his sense of language.
John Scalzi wrote about his first experience with The Martian Chronicles in an introduction to the Subterranean Press edition, available online as Meeting the Wizard:
The Martian Chronicles is not a child’s book, but it is an excellent book to give to a child—or to give to the right child, which I flatter myself that I was—because it is a book that is full of awakening. Which means, simply, that when you read it, you can feel parts of your brain clicking on, becoming sensitized to the fact that something is happening here, in this book, with these words, even if you can’t actually communicate to anyone outside of your own head just what that something is. I certainly couldn’t have, in the sixth grade—I simply didn’t have the words. As I recall, I didn’t much try: I just sat there staring down at the final line of the book, with the Martians staring back at me, simply trying to process what I had just read.
Obituaries are out there by the score, like this one in the New York Times and another good one in The Guardian, so there is no need to run through all the statistics. But it’s fun to hear the stories around the edges. Back in 2006, the public library in Fayetteville, AR was highlighting Fahrenheit 451 in a city-wide ‘Big Read’ event. Bradbury was corresponding with the assistant director of the library about all this and in the process reminisced about the composition of “The Fireman,” the short story from which Fahrenheit 451 would eventually grow. Shaun Usher recently reprinted the letter on his wonderful Letters of Note site, from which I quote:
I needed an office and had no money for one. Then one day I was wandering around U.C.L.A. and I heard typing down below in the basement of the library. I discovered there was a typing room where you could rent a typewriter for ten cents a half hour. I moved into the typing room along with a bunch of students and my bag of dimes, which totaled $9.80, which I spent and created the 25,000 word version of “The Fireman” in nine days. How could I have written so many words so quickly? It was because of the library. All of my friends, all of my loved ones, were on the shelves above and shouted, yelled and shrieked at me to be creative. So I ran up and down the stairs, finding books and quotes to put in my “Fireman” novella. You can imagine how exciting it was to do a book about book burning in the very presence of the hundreds of my beloveds on the shelves. It was the perfect way to be creative; that’s what the library does.
This morning my newspaper contains an account of Bradbury’s distrust of colleges and universities. He liked libraries better and thought they were the place to learn, the place where he could tap the energies of the great writers who had gone before and fine-tune what he called his “passionate output.” Passionate it was, and so was the man in every respect. Just last week he appeared in The New Yorker to discuss his inspiration, describing his frenzy over reading early issues of Hugo Gernsback’s Amazing Stories and remembering in particular one magic discovery that would change his life:
My next madness happened in 1931, when Harold Foster’s first series of Sunday color panels based on Edgar Rice Burroughs’s “Tarzan” appeared, and I simultaneously discovered, next door at my uncle Bion’s house, the “John Carter of Mars” books. I know that “The Martian Chronicles” would never have happened if Burroughs hadn’t had an impact on my life at that time.
I memorized all of “John Carter” and “Tarzan,” and sat on my grandparents’ front lawn repeating the stories to anyone who would sit and listen. I would go out to that lawn on summer nights and reach up to the red light of Mars and say, “Take me home!” I yearned to fly away and land there in the strange dusts that blew over dead-sea bottoms toward the ancient cities.
So much of what we try to do here involves engaging the imagination. Neil deGrasse Tyson likes to quote Antoine de Saint-Exupéry on the topic: “If you want to teach someone to sail, you don’t train them how to build a boat. You compel them to long for the open seas.” Ray Bradbury was not a boat-builder, and in his science fiction he was content to leave the details of construction to others. His driving wish, deep and unquenchable, was to awaken in his readers the same passion for raw experience he found within himself, by invoking the small events that define all our lives. Midnight carnivals, small town summers and rockets cutting into the dawn became his working materials, lighting fires that for many of us will burn long after he is laid to rest.
by Paul Gilster | Jun 6, 2012 | Sail Concepts |
I’ve been thinking about solar sails these past few days, a topic that inevitably invokes Arthur Holly Compton, who first demonstrated that x-rays have particle-like properties. Compton’s experiments in 1923 produced a body of work for which he would receive the Nobel Prize in Physics later that decade. Thanks to him we learned that while photons have no mass, they do have momentum, a useful fact for space exploration in that momentum can be transferred to a thin reflective sail, like the Japanese IKAROS that was successfully launched and tested in space in 2010. No question that the force is tiny — a sail would have to be a square mile in area to feel just five pounds of force at the Earth’s distance from the Sun.
The beauty of the sail, of course, is that it can keep producing thrust as long as it’s in sunlight. But how to increase the thrust? In an essay in his new book Going Interstellar (edited with Jack McDevitt and just out from Baen), Les Johnson notes that if we wanted to equal the thrust produced by one Space Shuttle engine, we would need a sail of one hundred thousand square miles in area, which works out to the surface area of Alabama and Mississippi combined. Working at Marshall Space Flight Center in Huntsville, Johnson knows the terrain of which he speaks. He also knows that we’re not about to start producing solar sails of this magnitude any time soon.
The alternative is to take advantage of the inverse square law, which says that moving the sail twice as far from its light source will result in its receiving four times less illumination. A similar move to four times the distance drops the illumination to one-sixteenth of its former value. The flip side of this is that reducing the distance to one-half its former value results in four times the force, and so on. You can see where this is heading: Johnson is building us up for a close solar pass, what sail experts Gregory and James Benford call a ‘Sundiver’ maneuver. Get your sail to swing close enough to the Sun and you get quite a push.
It’s interesting to speculate on just how big that push could be. Here we can take advantage of Gregory Matloff and Roman Kezerashvili (New York City College of Technology, CUNY), who have been massaging the numbers on a sail one mile in diameter moving to within nine million miles of the Sun. They find that a sail of this class could achieve a Solar System exit velocity of 250 miles per second. Johnson talks about all this in miles per second but let’s switch to kilometers, which is my normal practice here. 250 miles per second works out to about 400 kilometers per second, which we can usefully compare to Voyager 1’s 17 km/sec, as Johnson does:
A craft traveling this fast would pass the Earth in four days, Jupiter in twenty-one days and reach the Alpha Centauri system in just over three thousand years. By comparison, the fastest rocket we’ve ever sent into space won’t cover the distance to the Alpha Centauri system for another seventy-four thousand years! By increasing the sail size and keeping the payload mass the same, we can see an engineering path to building a sail that could cover this immense distance in about a thousand years. For you and me, there isn’t much difference between a thousand years and seventy-four thousand years. But in the lifetime of civilizations, the difference between these numbers is significant.
The difference is history. Go back 74,000 years and you are in the realm of archaeology, looking for the remains of nomadic, pre-literate cultures. Go back a thousand years and you are dealing with recorded human history. Ralph McNutt, who is doing such splendid work on interstellar concepts with the Innovative Interstellar Explorer design, once in a NIAC study worked out a trajectory involving a close solar pass that would get a payload to Epsilon Eridani in 3500 years, which he noted as the lifetime of the Egyptian empire. A 1400 year mission to Alpha Centauri would get the payload there in a time period as long as some buildings — the Hagia Sophia in Constantinople and the Pantheon in Rome — have been maintained.
And what would happen to the crew in that amount of time? One solution is the ‘generation ship’ that sees the birth and death of numerous generations on its way to the stars. But in a short story Johnson wrote for the same Going Interstellar volume, the author speculates about another method. The crewmembers of the long-haul starship in “Choice” are put into suspended animation, their minds kept active through hundreds of years of virtual reality simulations, just as their bodies are occasionally adjusted and massaged by intelligent machinery.
Thus the experience of the story’s protagonist, Peter Goss:
He, and every member of the crew, had programmed into the computer system their general wishes for the type of virtual reality scenarios they’d wanted to experience during the long voyage. The liquigel and the regular neuromuscular stimulation that went with it had kept their bodies alive and in peak condition while they slept. The VR scenarios had done the same for their minds and right now Goss wished he were one of the crew, blissfully unaware of the impending crisis, living out some extended adventure in a dream-like stupor. But it was a fleeting thought. He’d always preferred reality to the VR sims — that was one of the reasons he’d volunteered for the trip to Epsilon Eridani. Goss had to get away from the existential existence that was slowly creeping across the Earth and sapping the lifeblood out of the people there.
Missions of vast duration pose problems we haven’t even thought of, and the one Johnson dreamed up is a beauty. If, having experienced your choice among thousands of available VR simulations for a thousand years, you realized you were approaching your destination, would you really want the journey to end? After all, being awakened to land on a planet would put you back on your normal biological clock. No more simulations stretching out before you with no end in sight, but rather a far shorter and physically demanding existence creating a colony on what might be a difficult and chancy world. Obviously, I’m not going to give away the ending.
Going Interstellar is an intriguing volume. I’ve only read the two Johnson essays and another by Greg Matloff on antimatter propulsion, but you’ll find the major ideas for getting us to the stars here, though the editors are quick to note that they cover only the propulsion options open to us with known physics. You’ll find no warp drives or hyperspace vehicles in these pages. You will get, in addition to the work of scientists, stories by science fiction writers like Ben Bova, Michael Bishop and Mike Resnick. The combination reminds me of Arthur C. Clarke’s Operation Solar Sail (1990), which took on every aspect of sail traveling through both a fictional and non-fictional perspective.
It’s a good combination when you’re offering up a potpourri of current thinking on the intractable issue of starflight. We’ll be coming back to this book as I get deeper into it.
by Paul Gilster | Jun 5, 2012 | Deep Sky Astronomy & Telescopes |
Back in 1997, astronaut John Grunsfeld pulled off one of the great radio gags of all time by calling in to National Public Radio’s ‘Car Talk’ program while orbiting the Earth aboard Atlantis in STS-81. He had called to complain about his vehicle’s performance which, as he told the show’s hosts — known as ‘Click and Clack, the Tappet Brothers’ — was driving him crazy. His troublesome ride would buck and rattle and run loud for four minutes, then get much quieter for another ten, and then the engine would quit. Odd behavior for any vehicle but the Space Shuttle, as Click and Clack eventually realized, and a memorable exploit for Grunsfeld’s second Shuttle mission.
Image: A bumpy ride to orbit — liftoff of STS-81 on January 12, 1997. Credit: NASA.
Grunsfeld is more commonly remembered as a repairman for the Hubble Space Telescope, a task he performed on three subsequent missions without the help of ‘Car Talk.’ Now the astronaut, with over 58 days in space and eight space-walks, is in the news again, this time with a plan that would not only save NASA money on a future mission design but rescue equipment that is otherwise unused. Grunsfeld has presented a plan to use one of two space telescopes the size of Hubble that were originally designed as spy satellites and re-purpose the instrument toward deep space exploration. Its uses in studying dark energy and exoplanets are among the attractions.
An even bigger attraction is that this hardware is sitting in storage waiting for a ride. The indispensable Dennis Overbye has the story in yesterday’s New York Times, where he discusses what Grunsfeld had to say on Monday at a meeting of the National Academy of Sciences in Washington. The telescopes themselves are in a ‘clean room’ in Rochester, NY, the property of ITT Exelis, an aerospace and technology company headquartered in McLean, VA. The National Reconnaissance Office is ready to pass them along. Overbye offers a description:
Dr. Grunsfeld described the telescopes as “bits and pieces” in various stages of assembly, lacking a camera and other accouterments, like solar panels or pointing controls, of a spacecraft. “We can’t say what they were used for,” he said.
A spokeswoman for the National Reconnaissance Office, Loretta Desio, said, “This is not something we’re going to talk about,” adding, “We’re hoping this becomes a NASA story.”
The two telescopes have a 94-inch-diameter primary mirror, just like Hubble, but are shorter in focal length, giving them a wider field of view: “Stubby Hubbles,” in the words of Matt Mountain, director of the Space Telescope Science Institute, adding, “They were clearly designed to look down.”
But astronomers are telling Grunsfeld they can also be used to look up and out. The question of the moment: Could a repurposed telescope like one of those at ITT Exelis be folded into the WFIRST concept? The Wide Field Infrared Survey Telescope, recommended by the National Academy of Sciences in 2010, has been slated for a launch in the mid-2020s, if then, but the $1.5 billion project could be completed sooner and at lower cost — about $250 million lower — if one of the repurposed telescopes were to be used. Overbye points out that the telescope would have twice the diameter as the one being considered for WFIRST, allowing operations in geosynchronous Earth orbit rather than the solar orbit previously anticipated, and offering a faster sky survey as well as more efficient data downloads.
And yes, suitably modified, one of these telescopes could also be used as an exoplanet hunter. Grunsfeld, who is now NASA associate administrator for space science, has worked out the initial details with a team of astronomers, who seem enthusiastic about the prospect of getting WFIRST — or something perhaps even better — into the sky in an earlier time frame. Could we see a mission using a telescope with four times the light-gathering power of the WFIRST concept ready to fly as early as 2020? The opportunity is there even if a new cost estimate is not, but surely the possibility will come in for consideration at the highest levels. Unused equipment sitting in storage is made to order for economic times like these.
Addendum: This story has plenty of layers to it. See, for example, These Are Not the Telescopes NASA Was Looking For, which just appeared on NASA Watch. Also, check this site (thanks Bill Higgins) and find “Implication of New Developments for the Astronomy and Astrophysics Decadal Survey” — Alan Dressler, Observatories of the Carnegie Institute. Also see “New Developments in Astronomy and Astrophysics” — Paul Hertz, Associate Administrator for NASA Science Mission Directorate (SMD), linked off the same page. Finally, Marcia Smith has a good overview of the initial announcement on SpacePolicyOnline.com.
by Paul Gilster | Jun 4, 2012 | Exoplanetary Science |
While we wait for the last transit of Venus of the century, it’s worth remembering how tricky transit studies can be when we push them out to exoplanetary distances. You would think that catching a transit of a planet like Venus, closer to us than the Sun, would be simplicity itself, but the orbital planes of Venus and the Earth are not precisely enough aligned to allow for more than a pair of transits followed by over a century of waiting for the next. I’ve just received a copy of Mark Anderson’s The Day the World Discovered the Sun (Da Capo Press, 2012) and will be writing about 18th Century transit studies and their impact in coming weeks.
The transits Anderson writes about and the expeditions that ranged the globe to study them played a role in helping astronomers understand the dimensions of the Solar System. And you can see that if Venus is a challenge, tracking planets around other stars will push our technology to its limit. Nonetheless, we’re getting quite good at teasing information out of our data, as the planet known as HD 189733b continues to show us. It was just 16 months ago that carbon dioxide and methane were discovered in the planet’s atmosphere. Moreover, the work was done using a 3-meter instrument located at NASA’s Infrared Telescope Facility at Mauna Kea that ranks no higher than 40th among our ground-based instruments.
Sodium had already been found in the atmosphere of HD 189733b, and now comes word that astronomers working at the Hobby-Eberly Telescope at UT Austin’s McDonald Observatory have identified interactions with the parent star that show the planet is slowly dissolving. 63 light years away in the constellation Vulpecula, the planet is losing hydrogen in great streamers that are much hotter than previously thought, an indication that flare activity on the star is interacting with the atmosphere of the planet. Given the proximity of planet to star, that’s not entirely surprising: HD 189733b, a ‘hot Jupiter,’ orbits 10 times closer to its star than Mercury to our Sun.
Probing an exoplanet’s atmosphere is made possible by its transits as seen from Earth, as Seth Redfield (Wesleyan University) explains:
“Each time the planet passes in front of the star, the planet blocks some of the star’s light. If the planet has no atmosphere, it will block the same amount of light at all wavelengths. However, if the planet has an atmosphere, gases in its atmosphere will absorb some additional light.”
Image: The dotted line shows the planet’s orbit around the star HD189733. The planet orbits the star once every 2.2 Earth days, crossing the face of the star well below its equator. The small circles indicate the planet’s location during each of Seth Redfield’s more than 200 Hobby-Eberle Telescope observations over the course of one Earth year. The red circles indicate observations during transit; the rest of the circles denote out-of-transit observations. Credit: S. Redfield/T. Jones/McDonald Obs.
It was Redfield who first identified sodium in HD189733b’s atmosphere using the same instrument, based on observations that compared the spectrum of the light collected during a transit with the light of the star by itself. As huge as this planet is — 20 percent more massive than Jupiter — it blocks only 2.5 percent of the star’s light, along with another 0.3 percent that is accounted for by the planet’s atmosphere. Exoplanetary atmosphere studies using transits are built around the slight differences that are revealed when the planet passes in front of the star. It’s worth reflecting on all this as we wait for tomorrow’s transit of Venus and ponder how far transit studies have taken us since the first scientific expeditions set out to study them.
The paper is Jensen et al., “A Detection of Hα in an Exoplanetary Exosphere,” Astrophysical Journal Vol. 751, No. 2 (2012), p. 86 (abstract / preprint). More in this McDonald Observatory news release.
