One night about ten years ago I was walking down a quiet road on Emerald Isle, NC, the spring air spangled with stars, when a meteor flamed across the sky with such vehemence that I fully expected to hear the sound of an impact. I didn’t, of course, and on the normal scale of things, I wouldn’t be likely to. Chances are that even if the meteor did survive the fall to Earth, to become one or more of the meteorites sought by scientists as interesting chunks of the early Solar System, it landed far away and was much smaller in size than its trail seemed to imply.
Then I looked at Alan Dyer’s post on the recent meteor in Alberta, one that Dyer has illustrated with videos of the event. Taken from this week’s Carnival of Space, Dyer’s account points out that Alberta is a fine hunting ground for meteorites, but even the flat prairie can be tricky to search when you’re dealing with a momentarily visible event, a large search area and no reports of an object falling nearby. I also wondered if the average pedestrian that night wouldn’t have instinctively ducked.
The November 20 meteor over Alberta reminds us of the still unsettled state of the Solar System, and the danger that objects larger than this one might pose. Check the replay from an RCMP officer’s dashboard camera shown below, spectacular in the bright trail cutting across the sky and the fireball that follows, and imagine what might occur with an object a hundred times as large. A small near-Earth object could be far larger than the 1-10 ton meteor seen by Albertans, which is now thought to have been about as large as a chair, or maybe a desk.
Some 600 times brighter than the full Moon, it made for quite a spectacle. No wonder the local media were swamped with calls. I also notice that One Astronomer’s Noise gives a nod to a new theory of an asteroid impact that may have occurred over 2000 years ago near present-day New York City. A team from Harvard has found carbon spherules of the sort formed by extreme pressures — usually the sign of impact ejecta — in Hudson River silt. Did a 100-meter asteroid create these materials, and the tsunami whose evidence the Harvard researchers are now studying along the New Jersey and Long Island coasts? Can a crater be located?
Every major meteor sighting like the one that lit up the Albertan skies is a chance to remind the public that a prudent policy of near-Earth object detection is essential in safeguarding our future. Along with that realization comes the knowledge that a major thrust of our space program must be to develop methods of asteroid deflection in the event a serious Earth-crosser is discovered on a collision course. Some would argue that we might not need to deploy such technology for thousands of years. True enough, and I’m a gambler by nature, but this is one bet I’m not willing to take. Let’s develop the tools and sleep better at night.
Addendum: Reports from the Associated Press now say that meteorites from this event have been found near the Battle River along the rural Alberta-Saskatchewan border. And here’s a story from the Whitecourt Star on a much older crater that has now been identified in Alberta.
The phrase ‘liquid water’ is enough to quicken the pulse of the steeliest-eyed astrobiologist. We’ve long defined the concept of a habitable zone — that zone around a star in which life might flourish — by the presence of liquid water at the surface. But as we start pondering liquid water beneath the ices of outer satellites like Europa, we extend our investigations in exciting new ways. No wonder the new evidence of liquid water inside Enceladus received such attention in the mainstream media before the terrible news from Mumbai took center stage.
Image: In this artist’s concept, the Cassini spacecraft makes a close pass by Saturn’s inner moon Enceladus to study plumes from geysers that erupt from giant fissures in the moon’s southern polar region. Credit: Karl Kofoed (Drexel Hill, Pennsylvania).
On one level, liquid water on such cold, distant worlds is exciting because of the possibility of finding life that has arisen completely independent of what happened on Earth. At another, it’s energizing because it raises the prospect of other places where we might get further surprises. Joshua Colwell (University of Florida), who works on the Ultraviolet Imaging Spectrograph (UVIS) team supporting the Cassini mission, says it well:
“There are only three places in the solar system we know or suspect to have liquid water near the surface. Earth, Jupiter’s moon Europa and now Saturn’s Enceladus. Water is a basic ingredient for life, and there are certainly implications there. If we find that the tidal heating that we believe causes these geysers is a common planetary systems phenomenon, then it gets really interesting.”
Interesting indeed. Those remarkable geysers emanating from Enceladus’ south pole could involve water vapor escaping from a liquid underground source, becoming ice grains as they make their way through cracks in the crust. The recent work shows that the water vapor forms narrow jets as it emerges, a finding that seems to demand temperatures close to the melting point of ice to account for the observed behavior. The study was made during a stellar occultation as the plumes passed in front of the distant binary star Zeta Orionis, measuring the jets’ water vapor content and density (the secondary star was not a factor in the observations).
Four high-density water vapor jets were revealed against the background plume in this study, and it is their density and presumed temperature that support the liquid water model. All of which is enough to keep Enceladus squarely in Cassini’s sights as the spacecraft continues its extended mission, which lasts for two more years. The paper looks at competitive models, including the possibility that the jets are caused by the evaporation of volatile ices that are exposed to space when new vents open on Enceladus. It’s compelling that the timing of the jets in relation to the moon’s orbit around Saturn fails to coincide with this tidal model, but we have much to learn before declaring Enceladus a likely abode for life.
The paper is Hansen et al., “Water vapour jets inside the plume of gas leaving Enceladus,” Nature 456 (27 November 2008), pp. 477-479 (abstract).
When you’re thinking long-term, a period of 5.7 years seems like a mere blip in time. But NASA’s Long Duration Exposure Facility, deployed from the shuttle Challenger in 1984 and returned to Earth after 32,422 orbits, is a small-scale experiment that points to much weightier objectives. Think about the Voyager spacecraft, launched in 1977 and still operational after thirty-one years. Now ponder journeys to the heliopause and beyond, and potential missions to other stars that could last centuries. To learn how materials hold up in the space environment, we use tools like LDEF to collect data that can be gathered nowhere else.
57 experiments were mounted in 86 trays on the outside of the spacecraft, involving more than 200 principal investigators from private companies, universities, NASA centers, the Department of Defense and eight foreign countries. The idea was to study what happened to various materials when they were exposed to space, and as the Long Now Foundation’s Kevin Kelly noted earlier this year, each of the 86 panels has a certain ‘geeky modernist charm,’ the sort of look that wouldn’t be out of place at the trendiest modern art venues. Here you can see some of the panels on the LDEF spacecraft during the orbital experiment.
Indeed, writer and artist Jaime Morrison was so taken with these panels that he created an online gallery of them. For him, the LDEF spoke on many levels:
…it brings to mind the abstraction of certain painters, a gridded and measured minimalism in graphic design, failed utopian architecture, and the shapes and surface textures of every science fictional interior ever put on film. Add to that the subtle color palette peppered here and there with super saturated counterpoints, the unintentional, almost accidental, nature of its beauty, and (having been well battered during its 32,422 Earth orbits) the indelible stamp of decay…
And indeed, these LDEF panel shots are unforgettable in their own way. High technology as art is part of the human impulse, one that will surely accompany us on our way to the stars. The LDEF, along with the current Materials International Space Station Experiment (MISSE), is part of the enterprise of developing long-term solutions to problems, learning how to build structures that can experience space not for years or even decades but centuries. The distances involved in exploring the outer Solar System and beyond demand such thinking, not to mention the real possibility that we will one day choose to deploy large structures in space or on other worlds not just for research but lifelong habitation.
But there is another long-term issue that these panels speak to. Science itself proceeds through the efforts of researchers whose work contributes in ways small or large to the breakthroughs that actually make the news and change the course of civilizations. A breakthrough in interstellar propulsion would open possibilities we only dream about today, but if it comes, such a breakthrough may not appear for decades or centuries. The chastening demand of science is that without knowing the result, we continue to labor at the details, knowing that we may be playing only a small part in what could become an outcome that benefits all of humanity. Can the modern ego, fixated on quick gratification and immediate results, continue to adapt to what Tennyson called ‘the long result of time?’
Let’s hope and assume so. The danger of demanding quick fixes, as desirable as they may be, is that if they do not emerge, we may lose track of the ultimate goal, and of the fact that science is not about ego or personal success as much as it is about moving knowledge forward. Ad astra incrementis, the motto of the Tau Zero Foundation, reminds us that steps taken one by one must accumulate to produce the desired result, or as Lao-Tsu once said, “You accomplish the great task by a series of small acts.” And you do this without knowing whether you will see the outcome, or whether it will be reserved for your great-grandchildren or even, perhaps, theirs. In the grand scheme, what matters more than yourself is the goal.
As we learn more about cosmic rays, it becomes clear that these incoming particles — protons and electrons accelerated to high energy levels — do not reach us uniformly. Just a few days ago we saw that the ATIC (Advanced Thin Ionization Calorimeter) experiment had revealed a source of cosmic rays relatively close to the Earth. Now the Milagro Gamma-Ray Observatory, based at Los Alamos National Laboratory, has found two such cosmic ray ‘hot spots.’ Again we are looking at a source of high energy cosmic rays not terribly far (in galactic terms) from our planet.
Jordan Goodman (University of Maryland) is principal investigator for Milagro:
“These two results may be due to the same, or different, astrophysical phenomenon. However, they both suggest the presence of high-energy particle acceleration in the vicinity of the earth. Our new findings point to general locations for the localized excesses of cosmic-ray protons observed with the Milagro observatory.”
Milagro has been monitoring the entire northern hemisphere sky since 2000, recording over 200 billion cosmic ray collisions with the atmosphere. Such collisions create a shower of secondary particles that reach the surface, collisions now observed in sufficient numbers for the Milagro collaboration to see statistical peaks like the two most recently observed. The results are intriguing because the magnetic field of the Milky Way deflects cosmic rays, making it difficult to pin down their source. Now we see peaks that imply sources closer to our planet.
Image: An international team of researchers, using Los Alamos National Laboratory’s Milagro observatory, has seen for the first time two distinct hot spots that appear to be bombarding Earth with an excess of cosmic rays. The hot spots were identified in the two red-colored regions near the constellation Orion. Credit: John Pretz.
So what is the source of these phenomena? And why are these peaks found to be stronger in winter than in summer? All we can say at present is that they raise more questions than they answer, including the issue of how cosmic rays originate, and the more immediate question of whether the Solar System’s movements through the interstellar medium may have something to do with how they arrive. That latter issue points out how little we know about the heliosphere, and how much we could use a dedicated mission to this distant region. Note this, which I’m drawing from an article on the American Physical Society site by Karl-Heinz Kampert (University of Wuppertal, Germany):
Some clues may come from the actual sky position of the hot spots… The Milagro team noticed a directional coincidence of the stronger of the two hot spots with the heliotail. The heliotail is located in the direction opposite to the motion of the solar system with respect to the local interstellar medium (ISM), but there is no model of cosmic-ray acceleration in this region, so it may be purely coincidental.
Yes, and there’s also the fact that the hot spots encompass the Geminga pulsar that resulted from a relatively nearby supernova. Are the hot spots related to the supernova event, or is there some other acceleration mechanism nearby that can account for the high energies of these cosmic rays? We need more data. The Tibet Air Shower Gamma Array experiment has collected a huge amount of data (more than Milagro), within which are clues to what may be another cosmic ray ‘hot spot’ near Cygnus. As Kampert notes, getting the data from these teams together for refinement is a logical next step.
The paper is Abdo et al., “Discovery of localized regions of excess 10-TeV cosmic rays,” Physical Review Letters 101, 221101 (24 November, 2008). Abstract available. The Kampert article is “Puzzling Hot Spots in the Cosmic-Ray Sky,” Physics 1, 37 (2008), available online.
Addendum: Dennis Overbye discusses the ATIC findings, among other results, in this New York Timesarticle, looking at them in the context of a possible dark matter signature.
What might make a star particularly interesting from a SETI point of view? Bruce Cordell looks at the question in a post in the latest Carnival of Space, drawing on a JBIS article by Martin Beech (“Terraformed Planets and SETI,” February 2008). The method seems to be to examine the ratio of a star’s age to its Main Sequence lifetime.
Beech does this for 123 stars with known exoplanets, making the interesting point that terraformed planets might throw a particular observational signal in systems with the right ratio. Three are particularly promising for future study: HD4308, HD190360, and 70 Virginis. Pondering all this, Cordell writes:
If habitable planets are discovered near these or similar stars, ebullient Earth-bound astronomers contemplating interstellar voyages will check their spectra, to see if ‘the lights are on’ just in case any ETI’s are home.
A star of a certain age, in other words, may have been around long enough to allow an extraterrestrial civilization not only to emerge but to make its presence known to other observers, either intentionally or through evidence of planetary engineering. Cordell is right that we’ll be ebullient to find such a planet, but at this stage in the game, finding a potentially habitable planet around any star, regardless of age or possible inhabitants, is going to be cause for celebration.
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More on Dyson Spheres: Tibor Pacher writes with a pointer to an older proposal to search for Dyson-style engineering using the German ISOPHOT instrument, an imaging photo-polarimeter that was built for the ESA’s Infrared Space Observatory satellite. Here’s the essence of the proposal:
The program will be the first attempt to perform active SETI in the infrared using a spacecraft. A photometric survey, covering 3–60 microns, of several old main sequence stars will be performed in order to assess infrared excesses compatible with the presence of large astro-engineering products like Dyson spheres that emit a blackbody temperature of several hundred K. This survey shall identify candidates for Dyson spheres. In addition, a few objects which are known to show infrared excesses in the 12 or 25 micron IRAS measurements are considered for a detailed photometric investigation. The usage of the ISO satellite is crucial for the success of the program as only ISO currently offers, with its infrared photometer, the high sensitivity that is needed to detect the radiation of cold artificial structures superimposed on the several thousand K blackbody background spectrum of the host star.
As far as I know, the Infrared Space Observatory’s operational phase ended before any observations could be implemented — does anyone have further information? The paper is Tilgner and Heinrichsen, “A Program to Search for Dyson Spheres with the Infrared Space Observatory,” Acta Astronautica Vol. 42 (May-June, 1998), pp. 607-612.
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Centauri Dreams readers know all about Greg Laughlin’s hopes to create a dedicated radial velocity search for planets in the Alpha Centauri system. The UC-Santa Cruz planet hunter notes the key factors — brightness, age, spectral type, metallicity, orientation, and sky position — that make Alpha Centauri b “…overwhelmingly best star in the sky for detecting habitable planets from the ground and on the cheap.”
So I’ve been wondering for some time how Laughlin reacted to recent work by Philippe Thébault and his collaborators, work that notes how unfavorable the environment around both Centauri stars is for planets to form. We know there are stable orbits around Centauri b, for example, and the right number of planetary embryos should produce terrestrial-class planets there. But if Thébault’s team is correct, the perturbations produced within this binary system, coupled with gas drag on the planetesimals, create a situation where the planetesimals don’t hold together after they collide because of high collision velocities.
The end of our hopes for the Centauri stars? In a recent post, Laughlin remains cautiously optimistic:
Even when confronted with these results, I’m still cautiously long Alpha Cen Bb. It’s not that I think the simulations are wrong or that there is any problem with the outcomes that they produce. Rather, I don’t think a high gas density in the inner AU of the Alpha Cen B disk is cause for alarm.
Why? Thébault uses a model consistent with the disk that produced our own Solar System, a set of conditions here referred to as the ‘minimum-mass solar nebula’ (MMSN). Adjust the parameters for Centauri b, though, and things begin to change, with embryos forming much further out from the star (Thébault saw areas outside 0.5 AU as hostile to planet formation, making habitable planets all but impossible). Laughlin again:
In a nutshell, I don’t see evidence that the MMSN is of any particular utility for explaining the extrasolar planetary systems that we’ve found so far, and hence I’m not depressed that high gas densities were required for Alpha Cen B to have fostered an accretion-friendly environment. Reconstitute, for example, the HD 69830 protoplanetary disk or the 55 Cnc protoplanetary disk. I’m plain skeptical of the validity of a fiducial MMSN scaling for the disks that orbited the Alpha Cen stars. The Alpha Cen binary has twice the total mass of the Solar System, and more than two thousand times the total angular momentum.
Which gets us back to radial velocity observations, and the compelling need to make them over the long observing runs that will tell us what’s really around the Centauri stars.
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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