The ExoClimes 2010 conference (“Exploring the Diversity of Planetary Atmospheres”) is well in progress in Exeter (UK) as I write, with its talks now being posted online and the hope that video of the presentations will soon be available on the conference site. Already the latest lingo is in the air, as in ‘Hermean,’ a term used by Brian Jackson (NASA GSFC) to describe hot, rocky exoplanets with tenuous atmospheres. The analogy is with Mercury, though these are even hotter places with magma oceans and melted surfaces, leading to what Jackson calls a ‘rock vapor atmosphere’ that just might be visible given sufficient spectral resolution.
But what catches my eye this morning, as I survey the ongoing conference buzz online from an ocean away, is Franck Selsis (Laboratoire d’Astophysique de Bordeaux) and his work on the atmospheres of short-period terrestrial exoplanets. Selsis is interested in the habitability of planets around M-dwarfs, noting their strong tidal interactions with their primary, the likelihood of tidal locking for planets in circular orbits, and the problems of atmospheric freeze-out on the dark side, calling for a heat redistribution mechanism to produce habitable surface conditions.
The broader issue, obviously of interest for this conference, is how a terrestrial world in the habitable zone of an M-dwarf would maintain an atmosphere in the first place. What Selsis argues in his presentation (I’m looking at his slides) is that finding and characterizing dense atmospheres on super-Earths is a major objective for understanding how such atmospheres form and survive. Active M-dwarfs show flare activity longer than the more sedate K and G-class stars, so we need to understand how atmospheres act here, and for that we need statistics.
That’s where it gets tricky. Transiting worlds within 10 parsecs aren’t going to offer the statistics we need, leading Selsis to speculate on whether we can measure the phase curves of non-transiting terrestrial exoplanets. If so, we can increase the number of targets by a factor of 10, but only if we can work out ways to detect and measure the infrared phase curve based on reflected light from the planet, as opposed to the primary and secondary transits of more established methods. A large, rocky planet around a low-mass M-dwarf is a good test case. Make it hot enough (0.05 AU) and you get a surface temperature that’s not too hot to hold an atmosphere, and you also get the highest planet/star contrast available for such a planet.
Other Exeter news: Sushil Atreya (University of Michigan) is interested in another kind of hot world, a version of Saturn’s moon Titan. Imagine a nitrogen-rich atmosphere like Titan’s in a temperature regime where chemical reactions are accelerating rather than moving in ultra-slow motion. A hot Titan would be a world much more like Venus than the Earth. But given the right migration scenario, such a world should be out there, its atmosphere filled with carbon soot and sulphur, in the grip of heat and abundant greenhouse gases. Atreya’s presentation lays out the case, and I’m looking forward to the video of it and other talks as ExoClimes 2010 continues.
We’re entering the era of the ‘super-Earths,’ when rocky planets larger than our own will pepper the lists of new discoveries. These smaller worlds will occasionally make a transit of their star, as does CoRoT-7b, and that’s when things really get interesting. After all, we know that secondary eclipses, in which a transiting exoplanet swings behind its star as seen from Earth, can be used to study distant atmospheres. The method collects light from both star and planet and, when the planet is hidden, subtracts the starlight to get the planetary signature.
Now Lisa Kaltenegger (Harvard-Smithsonian Center for Astrophysics) and colleagues Wade Henning and Dimitar Sasselov are advancing the idea that we can use near-term instrumentation like the James Webb Space Telescope to spot volcanic eruptions using these same methods. Their model is based on eruptions on an Earth-like planet, extrapolating from what happens on our world to suggest that sulfur dioxide from a major volcanic event on an exoplanet is measurable because it can be produced in huge quantity and is slow to wash out of the air.
Mount Pinatubo, which erupted in the Philippines in 1991, accounted for 17 million tons of sulfur dioxide blown into the atmosphere in a layer between 10 and almost 50 kilometers above the Earth’s surface. But we also have the example of the Tambora eruption of 1815, which was as much as ten times more powerful than Pinatubo. Tambora is the largest observed eruption in recorded history, an explosion that could be heard 2600 kilometers away. Fine ash particles stayed in the atmosphere for a period of years, and the summer of 1816 became known as ‘the year without a summer’ in the northern hemisphere , a climatic anomaly evidently related to the release of vast amounts of sulfur.
Eruptions of this magnitude don’t occur frequently on Earth, but there is no reason to think that young, rocky exoplanets would not be more volcanically active than our more mature world. And ponder the effects of tidal heating, not only on planets but also on their moons. From the paper:
Tidal heating may contribute significantly to volcanism for eccentric exomoons or eccentric planets in heliocentric periods of 20-30 days or less… Such tidal heating has the potential to generate from thousands to millions of times more internal heating than in the modern Earth. However, at the upper end of this heat range, magma is more likely to escape in a non-explosive pattern, or may simply emerge into lava lakes or magma oceans partly sustained by the high insolation values near stars, such as the magma ocean suggested for Corot 7b. Such extreme worlds may also be more likely to have a reducing atmosphere. Significant tidal activity can be stimulated in multi-body systems by secular perturbations, secular resonance crossings, or a deep and stable mean motion resonance, analogous to the Galilean moon system.
So the most extreme heating may well work against detectable volcanic activity, but tidal effects may be pronounced in more moderate scenarios:
Modest tidal heating cases may easily supply some exoplanets with both a 10x increase in the size and frequency of large eruptions, while simultaneously enhancing nonexplosive activity.
And that, of course, is only part of the picture. Volcanic activity may also be keyed to planetary age, with younger planets expected to have more residual accretion heat and higher radionuclides, while plate tectonic activity can increase the frequency of explosive volcanoes. The paper is careful to examine other mechanisms for heat escape in non-explosive events and notes that we don’t know whether hotter planets would necessarily show more explosive eruptions. Nonetheless, an Earth-like world less than thirty light years from the Sun should be a fair candidate for JWST studies that can help us put constraints on some of these variables.
Although it’s true that secondary eclipse studies give us a relatively crude picture of a planetary atmosphere, they do help us find particularly abundant molecules and provide us with a basic model that can be developed over time. This new work shows that in the best case scenario, volcanic features become visible at values between 1 to 10 times the Pinatubo eruption — the probability of observing an eruption of Pinatubo class is about 1 percent if four Earth-like planets are observed for one year, while a Tambora-size event could be detected with a 10 percent probability by observing roughly 50 such planets for two years. The paper concludes:
These observations becomes a very interesting option to characterize rocky planets, especially if one assumes larger, and/or more frequent eruptions than on Earth, or smaller host stars, where a planet in the HZ orbits closer to their stars, increasing the transit probability., or longer SO2 residence times than on Earth.
The paper is Kaltenegger et al., “Detecting Volcanism on Extrasolar Planets,” in press at The Astrophysical Journal (preprint).
My friend Tibor Pacher quotes from Hermann Hesse on the front page of his PI Club site: “To let the possible happen, the impossible must be tried again and again.” No one works harder at pushing the boundaries of the possible in terms of public outreach on interstellar topics than Tibor, whose efforts have ranged from the Faces from Earth project (championing messages from humanity on deep space missions) to the MiniSpaceWorld contest (soliciting ideas and designs for space-themed exhibits). In today’s essay, Tibor looks back at a memorable evening in his youth, and ponders the sources of inspiration even as he gears up Faces from Earth for a new campaign based on the Voyager missions and the deeper meaning of their ‘golden records.’
I remember a wonderful starry night at Lake Balaton in Hungary, some forty years ago in my childhood. In those times street light was much more sparse in the evening than today, even in such holiday locations as Balaton. We watched an open air movie and were on the way back to our vacation home. I’ve forgotten the movie but not the starry night with its blinking jewels.
That time I had already seen the fantastic adventures of the spaceship Orion – the now legendary Space Patrol series started on 17 September 1966 in Germany and came in early 1968 to Hungary – and some of the Apollo landings as well. Perhaps this night was the first one in my life as a then wannabe astronomer when I found myself pondering whether we could get to the stars one day and wondering what we would find there if we did.
Later, I became a theoretical physicist, studied cosmology, and tried to figure out if in our world there might emerge a hyperdrive like the one in Asimov’s Foundation universe (I did not succeed, unfortunately, but neither have I given up the search). Then my paths led me to very different, much more earthbound fields like business consulting on financial processes, which secured my living. I have seen lots of interesting companies, met people from very different countries from Kazakhstan to Georgia, Singapore to Sweden and Bosnia-Hercegovina, but after all this, I came to the conclusion that this kind of job is something which cannot satisfy my needs to learn more about the Universe.
So early this millenium I started once again to dig deeper into the really interesting things, to rediscover my early intellectual loves, topics like interstellar spaceflight and life in the universe. My notes tell me that it was the 2nd of July 2004 when the name peregrinus interstellar was born, which I now regularly use for my celestial wanderings. (The term “peregrinus” means “wanderer”, “stranger”, or “alien” and originates in ancient Rome, denoting people not having Roman rights. It is also the root for the word “pilgrim”. In Hungarian, the word “peregrinus” was also used in earlier times to mean a wandering student).
Now, six years later, I often remember that starry night forty years ago at Lake Balaton. These seemingly distinct events mark perhaps the two most relevant cornerstones on the way to my current projects, amongst them Faces from Earth. Surely like the old wanderers, looking at the stars I enjoy the beauty of the heavens, and, as many others, often pause for a moment to think about our place in the Universe. I also believe that it is good for a wanderer to be prepared for strange encounters, whatever nice places he approaches.
Humanity has made its first steps on the long path to the stars, having sent out the first ambassadors, the Pioneer and the Voyager probes, in the 1970’s. On these four probes there is a “visiting card”, the Pioneer plaques, and the Golden Records – attempts to tell as much as possible about the makers of the spacecraft, should they be found by some other species, or perhaps by our own descendants, in the future.
Since our vessels are actually uninvited wanderers into unknown territory, as Larry Klaes’ says, “…[this] makes it vitally important that some kind of relevant information about ourselves is placed on each and every spacecraft sent into the Milky Way.” Within the framework of Faces from Earth we aim to help in preparing our future interstellar wanderers – and all of us, who stay at home but perhaps will experience an encounter with E.T. – with information on Messages from Earth – history, rationale, possible effects on humanity, organizing events to educate the public about space and astronomy, and promotion of deep space missions supporting the creation of the next artifact messages to put on board.
To quote Larry again:
“The importance of being in essence respectful citizens of the galaxy and giving some kind of valuable legacy to our children is a driving force in the creation of Faces From Earth. It is designed to bring together people from multiple fields and disciplines across human culture to more fully represent the beings and items of our world to the Universe on all future deep space missions.”
You probably will understand why one of the Faces from Earth projects is especially important for me. This is the campaign series “E.T. Are You Out There?”, which introduces the notions of possible extraterrestrial life and interstellar messages to school students, and constitutes a part of our attempt to “give some valuable legacy to our children.” On May 19 of this year, we came together at 5:30 PM – school scheduling and some unfortunate circumstances prevented a couple of students from coming, so we had a familiar meeting with Arianna, Corvin, Louisa, Michel and Vincent (12 to 14 years old) in my home in Molfsee, next to Kiel, “the sailing city”. However, being such a small group we had the opportunity to go into lots of details, checking information in the Internet immediately – about the Viking experiments on Mars (searching for life indicators), the Grand Tour of the Voyagers (the rare lineup of the outer planets in the Solar System), and, of course, the chances to talk to E.T., to name but a few – before the exciting time of creating the pictorial messages and the preparation of the balloon payloads arrived.
Luckily, we had two balloons for each message :-) We went then to the “launch pad” – a couple of minutes walk to a gentle hill – and the countdown (we’ve got it, Space Patrol Orion) started: … drei … zwei… eins… zero: “Guten Flug” (good flight) – and the Molfsee messages began their journey. It is very improbable that anybody will ever read them, but we hope that the children, not only the five in Germany, but the other approximately 100 we reached on three continents with our first campaign in May 2010, will be proud of their first symbolic message to E.T. and inspired to learn more.
Our second campaign “E.T. Are You Out There? – The Voyager Campaign” has just started on 5th September 2010, the 33rd anniversary of Voyager 1’s launch, and runs until 26 September. We hope that many young school students and their educators will remember the celebration of the Voyagers, with their own messages painted and perhaps released in some enjoyable way, just as the kids did in May.
As you can see in our summary video of the May campaign, to send a message to a hypothetical E.T. can be a deeply human endeavour.
Sometimes as I click through imagery from spacecraft and observatories, I think about what the world was like before we had an Internet to deliver this kind of information. Consider the early surveys of the heavens, exemplified by William Herschel sweeping the sky in the late 1700s. Herschel’s survey would find a new planet, create a basic map of the Milky Way, and note the location of the ‘cloudy things’ called nebulae, many of which turned out to be galaxies in their own right. His lists and annotations would grow into the New General Catalogue, which identifies thousands of objects by the now familiar NGC numbers.
The sky is all about statistics, as Herschel saw. When you’re dealing with objects whose lifespan is far longer than a human’s, you try to understand them by looking at enough examples to see the objects at every stage of their existence. Ann Finkbeiner offers this lovely Herschel quote in her new book A Grand and Bold Thing (Free Press, 2010):
“[The heavens] are now seen to resemble a luxuriant garden, [and]…is it not the same thing, whether we live successively to witness the germination, blooming, foliage, fecundity, fading, withering, and conception of a plant, or whether a vast number of specimens, selected from every stage through which the planet passes in the course of its existence be brought at once to our view?”
And then there’s Fred Hoyle, who said, “The Universe is so vast, and the lengths of time…are so long, that almost every conceivable type of astronomical process is still going on somewhere or other.” Finkbeiner’s book is all about the Sloan Digital Sky Survey, placing it firmly in the context of earlier astronomical work while bringing home with clarity and conviction how the new tools at our disposal, from adaptive optics to light-absorbing CCDs, have changed the game. Go back to the mid-20th Century and ponder the first optical survey done with a camera, the Palomar Observatory Sky Survey done with Caltech’s 48-inch telescope on Mount Palomar.
Surveys and Their Limitations
The Palomar survey, begun in 1949, produced some four thousand glass photographic plates, and if you were going to be a thorough astronomer in that era, you would need a set of photographic prints of the plates ($14,000) or glass copies of them ($25,000). Find something odd in a radio or X-ray observation and you would take your data to the Palomar plates to see what you were detecting. With the coordinates established, you could then go to a telescope and take a spectrum of whatever you had found. Needless to say, there was no ready access to telescopes or databases of their observations through a network available in the office.
But that wasn’t the only thing wrong with the plate method. For one thing, although their resolution was excellent, the plates used grains of silver halide that darkened when exposed to light. Too much light caused the plates to saturate, sharply reducing astronomers’ ability to measure the brightness of an object. And like all photographic plates, the Palomar plates differed from each other, exposed at different times and under different conditions. The advent of CCDs meant we could start measuring light without saturation and with immediate response. Moreover, the brightness of an object could now be measured to exceedingly high levels of accuracy.
Compared to all previous methods, the beauty of a digital sky survey like the SDSS is obvious. Data go from telescopes into computer storage, from which computers everywhere can access them. But doing a digital survey was a job of mind-numbing complexity (and I’ll spare you the political and academic dimension, which Finkbeiner covers in great detail and with a whimsical verve). Here she describes what the the Sloan Digital Sky Survey was attempting to do:
The Sloan itself was a new creature, effectively a real-time robotic astronomer. The software needed to observe and record, then locate, characterize, identify, and archive. It needed to be able to handle at least a trillion bytes of data — a terabyte, a unit astronomers had never before had any cause to use — coming off the telescope at a rate of 17 gigabytes, 17 billion bytes, every hour. It needed to command the automation of the telescope and the observations so that the only people on the mountain would be a staff of professional observers to oversee and troubleshoot, and everybody else could stay home and download galaxies. It needed to take the data coming off the instruments — the camera and the spectrographs — and reduce it, that is, turn data from the CCDs into images and spectra, standardized so that the stars and galaxies and quasars all looked as though they’d been taken on the same night under the same conditions.
What changes we’ve seen. In the late 1980s, Finkbeiner writes, there were about 4500 astronomers in the US and ten large telescopes, the majority of which were private. An astronomer would make observations at such an instrument and return with plates that would be analyzed in isolation. Astronomers without private telescopes could use the National Science Foundation’s two national observatories, coping with the fact that the instruments were far oversubscribed. Even then, scientists labored without well calibrated archives. Some early Sloan participants contemplated putting their data on CDs and selling them for $20,000 per set.
Image: 2.5m dedicated SDSS telescope at Apache Point Observatory. Credit: SDSS.
Taking the Data Online
Digital networking, of course, changed the equation. Today we can take a quick trip online to the SkyServer, downloading data with abandon and the kind of ease that will have future generations wondering how earlier astronomers ever functioned with so few major instruments and such inaccessible data. Putting terabytes of data into an online gateway, though, first meant collecting the information. It was James Gunn (Princeton) who coupled the idea of using state of the art CCDs with a camera and spectrograph fed by optical fibers to take spectra of hundreds of galaxies at once. His story animates Finkbeiner’s account. Gunn’s notion just grew and grew: Let the camera and spectrograph be fixed to a telescope that can drift scan one strip of sky after another and you wind up with images and spectra of galaxies galore.
Gunn’s idea would galvanize the astronomical community. Listen to Finkbeiner as she describes the reaction of Tim Heckman (Johns Hopkins) upon reading the Sloan proposal:
…the Sloan was going to change the way astronomers without private telescopes worked: Instead of taking a couple of years writing and rewriting proposals for three clouded-out nights on a public telescope, you could just take the interesting question that occurred to you and find the data you needed in the library of the universe. And the interesting questions would not be just about large-scale structure: for every question in optical astronomy that Heckman could think of, the Sloan archive would have data. And the amount of data on each question would be orders of magnitude larger than it had ever been before.
Amazing what you can do with a 2.5-meter mirror. Amazing, too, how institutions and individuals can alternately work together and frustrate each other to the point where projects like the SDSS are brought within an inch of being canceled. Finkbeiner has the whole story, and it’s sharply etched with the personalities of its protagonists. But what a result: The SkyServer holds everything in the surveyed sky, everything available through spectra, every image in five colors, every object from star to galaxy to quasar sorted as required and available for data manipulation.
How big has the SDSS become?
By the end of 2003, Science magazine’s Breakthrough of the Year was the new standard model of the universe revealed by comparing the cosmic microwave background as measured by NASA’s WMAP satellite with the large-scale structure as mapped by Sloan. By mid-2004, Sloanies had written 400 papers, and non-Sloanies using Sloan data another 125. In August, Scot Kleinman, an Apache Point observer, went to the Fourteenth European White Dwarf Workshop in Germany and reported that nearly 40 percent of the talks mentioned the Sloan. A non-Sloanie attending an American Astronomical Society meeting said he was astounded at the way the Sloan permeated all the talks…In 2001 and 2006, of all the optical observatories — the Hubble Space Telescope included — the Sloan was the most productive; in the intervening years, no one bothered to rank observatories…. As of October 2009, 2,656 papers were based on Sloan data and were cited in other papers 100,000 times. A non-Sloanie at the Space Telescope Science Institute said that Sloan hadn’t even been on his radar, and now it was astronomy’s eight-hundred-pound gorilla.
The impact of the SDSS is undeniable, and it’s no surprise that the public impulse behind it has spawned further innovations like Google Sky, WikiSky, and the Galaxy Zoo. Sloan II followed, then Sloan III as astronomy continued to move from a solitary scientist on a mountain to group collaboration and papers with not one or two but 150 co-authors. Today large surveys like Pan-STARRS and the LSST are in the works and like the SDSS, they will be online. Astronomy has opened up, becoming more accessible for practitioner and amateur alike. What a sea-change we’ve witnessed, and the Sloan Digital Sky Survey has been in the thick of it, described in this new book with panache by a writer who knows her science as well as her verbal craft.
The book is Finkbeiner, A Grand and Bold Thing: An Extraordinary New Map of the Universe Ushering in a New Era of Discovery. New York: Free Press, 2010.
Terraforming is an extreme notion, modifying an entire planet to create a biosphere within which Earth-based live could thrive. But a recent BBC story (thanks to Erik Anderson for the tip) takes on a kind of terraforming that we’ve already accomplished on the South Atlantic island of Ascension. Up until now, I had always thought of Ascension in terms of the BBC transmitter there — in my shortwave days, I always knew who had a relay station where and on what frequencies. But the vision I had was solely of high-tech antennae amidst volcanic debris. Now I learn Ascension has its green side.
Image: British programmer and traveler Les Smith has made several trips to Ascension Island and has produced a wonderful photo log of his travels. This image shows the view looking down from Green Mountain. Further on in the story is a second image from Smith, this one of a garden showing how verdant some places on the island have become as a once barren landscape takes on new life.
David Catling (University of Washington) has been following the travels of Charles Darwin and investigating his association with botanist and explorer Joseph Hooker. Darwin reached Ascension in 1836 at the tail end of his epic voyage aboard the Beagle. The island in those days was, as the inhabitants of the more southerly island of St. Helena told him, no more than a cinder, a volcanic outcropping between Africa and South America, and a long way from each.
The description reminds me of Iceland, which can be unexpectedly verdant in places (particularly the southwest, south of Reykjavik), but which also houses landscapes that are positively lunar in appearance, so devoid of evident life in all directions that you are reminded sharply of the place’s geological immaturity. But just as Iceland has its areas of farmland and growth, so Ascension has acquired a green patina on Green Mountain, its highest peak. The difference is that Ascension’s burgeoning ‘cloud forest’ is entirely artificial. Catling speculates that Darwin had a hand in the eventual growth, which Joseph Hooker became instrumental in creating.
Darwin evidently goaded Hooker to advise the Royal Navy to begin sending trees to Ascension, the idea being to create more water for the growing naval base on the island. From the BBC story:
The idea was breathtakingly simple. Trees would capture more rain, reduce evaporation and create rich, loamy soils. The “cinder” would become a garden.
So, beginning in 1850 and continuing year after year, ships started to come. Each deposited a motley assortment of plants from botanical gardens in Europe, South Africa and Argentina.
Soon, on the highest peak at 859m (2,817ft), great changes were afoot. By the late 1870s, eucalyptus, Norfolk Island pine, bamboo, and banana had all run riot.
Back in England, Charles Darwin and his theory of evolution were busily uprooting the Garden of Eden.
But on a green hill far away, a new “island Eden” was being created.
The story goes on to quote Dave Wilkinson (Liverpool John Moores University), who discovered plants that seldom co-exist growing together on Green Mountain. Wilkinson is interested in the principles Ascension demonstrates, the notion that brute force terraforming should give way to helping life gradually transform an environment. Could such principles take hold on other planets? The answer is at the other side of a great and necessary debate, one that questions whether we have the right to impact possible life forms on other worlds, and whether even on a lifeless world, such terraforming is more important than preserving what nature hath wrought.
Meanwhile, Les Smith’s photography renews my interest in one day making the South Atlantic island tour, which would take in Ascension, St. Helena, and the incredibly remote Tristan da Cunha, along with a side journey to the Falklands. The Darwinian echoes at Ascension spur me on, as does interest in how the community on Tristan has survived its long isolation.
In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).
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