This is what a solar sail looks like in space. The images below were taken by a camera flown aboard the IKAROS mission and then separated from it using a spring, according to the Japan Aerospace Exploration Agency (JAXA).
These pictures (and you can find several more here) take me back to my first reading of Cordwainer Smith’s ‘The Lady Who Sailed the Soul,’ in which a far future sail mission involving a sail tens of thousands of kilometers across plays against the tangled relationship of two lives (full text here). IKAROS may be far smaller, but if seeing a deployed sail in space doesn’t fire the imagination, what will? A brief snippet from the story:
The first sailors had gone out almost a hundred years before. They had started with small sails not over two thousand miles square. Gradually the size of the sails increased. The technique of adiabatic packing and the carrying of passengers in individual pods reduced the damage done to the human cargo. It was great news when a sailor returned to Earth, a man born and reared under the light of another star. He was a man who had spent a month of agony and pain, bringing a few sleep-frozen settlers, guiding the immense light-pushed sailing craft which had managed the trip through the great interstellar deeps in an objective time-period of forty years.
“The Lady Who Sailed the Soul” was published in Galaxy‘s April, 1960 issue, and still has a prized place on my shelf, along with all the other Galaxy issues of that era. If you haven’t yet made the acquaintance of Cordwainer Smith (Paul Linebarger), I envy you. Not only did he lead an unusual life (scholar, diplomat, spy and successful author), but the images he created with his words offer up a far future that is at once alien and deeply human. I wish he could have seen these pictures.
IKAROS will now be used to measure the effect of photon pressure from the Sun even as the spacecraft team examines the effectiveness of the thin film solar cells built into the sail. Just how navigable will IKAROS turn out to be, and how much can it teach us about future sail deployment and operations? We learn more day by day as this extraordinary mission continues.
The release of the first 43 days of Kepler data has demonstrated just how powerful a planet-hunting technology we’ve put into space. Listen to principal investigator William Borucki (NASA Ames) in a video released yesterday by NASA television:
“We’re releasing data on 156,000 stars that we’ve been monitoring with the Kepler mission for 43 days, the first dataset. In these data are some 750 planetary candidates. Some of those are actual planets, some are false positives. Our science team is looking at 400 of those candidates with ground-based telescopes, to figure out which are planets, which aren’t.”
Borucki assumes about fifty percent of the candidates will be false positives, eclipsing binary stars, starspots, or other misleading signals. Now it’s in the hands of ground-based telescopes in the Canary Islands, Texas, Arizona and Hawaii to comb through these findings to make the call. The team is also releasing the data for the remaining 350 candidates to the world community of astronomers to assist with the analysis.
Addendum: The video mentioned above has suddenly gone private. I don’t know why, but will hope to post it again when it reverts to public access.
Ponder this: The number of planet candidates here is actually greater than the number of all the planets that have been discovered in the last 15 years. We could conceivably double the list of known exoplanets with these 43 days of data alone. And, obviously, Kepler is still on the job.
Dennis Overbye discusses Kepler’s data release policy, a subject we’ve examined here before, in a new article for the New York Times, from which this overview of Kepler:
…the treasure hunt for the end to cosmic loneliness continues.”The public wants to know whether there is life on other planets,” Mr. Borucki said, noting that it could take decades. The effort to get an answer, he said, reminds him of the building of the great cathedrals in Europe, in which each generation of workers had to tell themselves that “someday it will be built.”
“In a sense, we, too, are doing these things,” he said.
Well spoken. The Kepler work segues nicely into a new piece by astrobiologist and author Caleb Scharf (Columbia University), who discusses the search for habitable worlds in a guest post for Scientific American. Scharf makes the point that most stars can be described with only a few parameters. Analyze mass, age, and abundance of elements and it’s fairly easy to create the stellar taxonomy that categorizes them. Planets, however, are a different matter. With them, we consider orbit, type of primary, atmospheric composition, axial tilt, gravitational tides…
Well, you get the idea. The complete list takes in magnetic field, geology, chemistry and more. The problem this presents is that while we want to choose the right candidate planets to study for extraterrestrial life, we’re dealing with space-based observatories with finite resources. We’d like to come up with nearby stars to examine that are not so different from our Sun, but 75 percent of all stars are less than half as massive as Sol, and most nearby stars are red dwarfs like these, where planetary and stellar conditions may make life problematic.
What to do? Scharf suggests looking at the big picture by putting statistics to work:
Suppose there are biospheres scattered across many systems, perhaps driven by the same kind of microbial machinery that dominates our own. Conditions can vary tremendously among these worlds, but biospheres still persist. Environments on such planets may be held in subtly different equilibria than their sterile equivalents – seen through atmospheric composition, reflectivity, and temperature. No single world may actually present enough of a smoking gun to let us say, “there be life,” but put the data from all these planets together, and that signature might be detectable.
Could a statistical approach to astrobiology succeed? Scharf continues:
Statistics are wonderful, if finicky, things. They let us cut through the haze and see things we would otherwise never find. Suppose we accumulate crude, rudimentary data on not just a few planets, but on hundreds or thousands. No single observation of a planet may tell us if it is teeming with life, but the cumulative weight of different parts of the planetary zoo might at least tell us if there is life on some of them. By letting go of our desire to locate a single instance of life, we’d stand to answer the global question.
Interesting to keep this in mind as we learn more about Kepler’s findings. For Kepler is itself statistically based, looking at a huge number of stars with the expectation, now being borne out, that a number of these will have systems tilted just the right way so that we can observe planetary transits from our perspective here on Earth. Scharf explores the kind of signal we might dig out of the statistical noise in his Life, Unbounded blog, and it’s heartening to think that in an era when budget realities keep terrestrial planet finder spacecraft indefinitely shelved, we might still locate habitable worlds by virtue of big datasets and brute force computing.
If we ended last week on a high note with the successful deployment of the IKAROS sail, this week started equally well with the return of JAXA’s Hayabusa spacecraft, whose re-entry capsule has now been recovered from the Australian desert and is intact. We’ll learn once it gets back to Japan how much material from asteroid Itokawa it was able to acquire. But what an exciting finish to this mission, and what a accomplishment by JAXA to survive battery failures, communications problems, engine issues and more and bring this mission home.
The canister return is the fruit of a seven year journey that saw Hayabusa touch down on Itokawa back in 2005, and although the many glitches caused a three year delay in its return, Hayabusa may well offer us at least trace amounts of material from the asteroid, valuable in helping us understand not only the asteroid itself but also the early history of the solar system. We have so few instances of material recovered from space — Moon rocks, cometary dust (from the Stardust mission), solar wind particles (Genesis), and whatever Hayabusa bears — and we may now have new samples that have changed little since the beginning of our solar system. The return canister now awaits preparation and transit to the Sagamihara curation facility in Tokyo.
New CoRoT Planets (and a Brown Dwarf)
Meanwhile, we also launch the work week with more news from CoRoT, which has detected six new exoplanets and one brown dwarf. CoRoT works by measuring the decrease in a star’s light caused by the transit of a planet across its face as seen by the spacecraft, a method doubly valuable because it allows a determination of the planet’s radius. Follow-up Doppler studies can then make a determination of the mass of the object, and with mass and radius known, the mean density of the planet can be derived.
Image: CoRoT’s 15 exoplanets. Credit: CNES.
CoRoT’s new findings include CoRoT-8b, 70 percent of Saturn’s size and mass, and a string of ‘hot Jupiters’ — CoRoT-10b, CoRoT-11b, CoRoT-12b, CoRoT-13b and CoRoT-14b. The brown dwarf is CoRoT-15b, sixty times as massive as Jupiter. The extreme eccentricity of the orbit of CoRoT-10b sets it apart from the rest, while CoRoT-11b orbits a star that spins at a high rate. While our own Sun rotates approximately every 26 days, this star spins around its axis in less than two days. ESA’s Davide Gandolfi led the study of this world:
“This is the third exoplanet discovered around such a rapidly rotating star. Because of the fast rotation of its host star, such a planet could only have been discovered because it transits in front of it, thus only a transit-hunter, such as CoRoT, could have spotted it.”
CoRoT-11b represents deft work indeed, for a high rotational rate makes it difficult to achieve high-quality Doppler measurements that would reveal the presence of a planet. But the transit finding could then be corroborated by photometric and spectroscopic follow-up observations, allowing estimates of the planet’s mass — about twice that of Jupiter — and its radius, about 1.4 times that of Jupiter. Thus the transit technique (you can see the lightcurve below) allows us to home in on an exoplanet that Doppler studies alone wouldn’t have found, simply because the observational time required would have caused researchers to pick more likely targets.
Among the other planets, CoRoT-8b is noteworthy in being the smallest planet yet discovered by the CoRoT team after CoRoT-7b, a transiting ‘super-Earth.’ CoRoT-10b is intriguing because its eccentric orbit causes the amount of radiation it receives from its star to vary tenfold in intensity in short order. Current estimates are that the planet’s surface temperature may increase from 250 to 600 degrees Celsius in the space of its year, which lasts 13 Earth days.
Image: Phase-folded lightcurve of the transit of CoRoT-11b, as derived by superimposing all the transits observed in the lightcurve. The best-fit model (thick line) is plotted on top of it. Credit: D. Gandolfi [Gandolfi et al, 2010].
An upcoming paper on this work is Gandolfi et al., “Transiting exoplanets from the CoRoT space mission XII. CoRoT-11b: a transiting massive ‘hot Jupiter’ in a prograde orbit around a rapidly rotating F-type star,” submitted to Astronomy and Astrophysics.
Here’s something to put the cap on a scintillating week in space science. It’s from Hal Levison (SwRI), who has led an international team in computer simulations focusing on our Sun’s earliest days. It turns out that our older assumption that the Oort cloud of comets surrounding the Sun came from the Sun’s protoplanetary disk may not be accurate. Yes, our system produced comets, but not enough to account for the Oort’s entire population, which swarms in a vast sphere that extends half the distance to Alpha Centauri. Says Levison:
“If we assume that the Sun’s observed proto-planetary disk can be used to estimate the indigenous population of the Oort cloud, we can conclude that more than 90 percent of the observed Oort cloud comets have an extra-solar origin.”
Image: Comet McNaught, possibly an interloper from another star, according to recent work. Credit: Stéphane Guisard.
The process works like this: We believe the Sun formed in a cluster containing hundreds of closely packed stars. Each of these stars would have formed its own population of comets out of its circumstellar disk, and most of these comets, including those in our own infant system, would have been ejected by the gravitational effects of newly forming gas giants. Moving out into the cluster, they would have eventually been captured by other stars, just as our Sun would have captured its own share of comets as the cluster dispersed, the hot young stars blowing its gases into the void.
Our star’s early life, then, would have involved substantial sharing with nearby stars, all of which have now moved away. If this is true, then the Oort should house materials from a wide range of the stars the Sun was born with, and many comets, perhaps famous ones like Halley, Hale-Bopp and McNaught, are actually interstellar visitors now in the Sun’s gravitational thrall. Says Ramon Brasser (Observatoire de la Cote d’Azur): “The formation of the Oort cloud has been a mystery for over 60 years and our work likely solves this long-standing problem.”
The paper is Levison et al., “Capture of the Sun’s Oort Cloud from Stars in its Birth Cluster,” published online by Science June 10, 2010 (abstract).
For those of you interested in the key IKAROS post describing the final deployment of the sail, Lionel Ward has been so kind as to translate it in context. I’m leaving out the actual photographs, which you can see via the links posted in my previous IKAROS coverage — and also here in context — but here is the text from JAXA:
——-
2010?6?11?[??]?
A world first! Solar Powered Electrical Sail deployment and power generation is successful!
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On June 8th the finalization of the primary deployment was executed, and on June 9th the secondary deployment was executed.
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IKAROS’ state at the end of the primary is detailed over on the Ikaros blog.
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Upon sending the command to initiate secondary deployment, a state of nervousness persisted in the command center during the 46 second propagation delay (the separation from earth is 7.4 million km!) until the initial data could be seen.
That deployment had occurred normally was first able to be seen from from the spin rate data and the positioning data. Continuing, although only a part of the monitoring camera’s images were being down-linked, we were able to confirm the deployment from the images. During June 10th the sail spread out beautifully, images of the ‘stretched state’ were acquired, and the post-secondary deployment confirmation efforts ended with the sail confirmed as successfully deployed.
The simultaneously deployed thin film solar batteries’ power generation is confirmed – minimum success targets have been accomplished!! This realisation of solar sail deployment and power generation becomes a world first!
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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