by Paul Gilster | Nov 11, 2008 | Astrobiology and SETI |
Using eleven of the Allen Telescope Array’s 6.1-meter dishes, the SETI Institute and the Radio Astronomy Laboratory at the University of California (Berkeley) have detected the New Horizons spacecraft on its way to Pluto/Charon. New Horizons transmits an 8.4 GHz carrier signal that showed up readily on the SETI Prelude detection system. What I hadn’t realized was that snagging distant spacecraft transmitters is a standard part of SETI operations, as Jill Tarter notes in this brief article on the event posted at the New Horizons site:
“We look forward to checking in with New Horizons as a routine, end-to-end test of our system health. As this spacecraft travels farther, and its signals grow weaker, we will be building out the Allen Telescope Array from 42 to 350 antennas, and thus can look forward to a long-term relationship.”
Image: New Horizons as tracked by the Allen Telescope Array. This plot shows 678 hertz (Hz) of spectrum collected over 98 seconds. The New Horizons signal can be easily seen as a bright diagonal line, drifting at rate of -0.6 > Hz/second. Credit: SETI Institute.
Just how long-term a relationship it may be is shown by this second image, the result of combining fifteen of the ATA’s antennae in October to detect the carrier from Voyager 1. The most distant of all man-made objects, Voyager transmitted from 108 AU, a signal described by Tarter as reliable and ‘…with a very high signal to noise ratio.’ New Horizons may be a newcomer compared to the 37-year old Voyager, but it will doubtless offer fodder for the ATA’s antenna farm for decades to come. The method at work here is called ‘beamforming,’ a way to process the incoming signal that allows multiple antennae to function together with maximum directionality.
Image (click to enlarge): Integrated power from Voyager 1 spacecraft over 192 second observation. Credit: SETI.
Combining signals from a host of different antennae so that detectors can do their work is no easy task, but it’s heartening to this SETI skeptic that the capabilities of the Allen Array are wide. Tarter described them in a recent Space.com posting:
One of the good things about the ATA is that there are likely to be many stars that are visible at any one time within its large field of view, so with multiple beamformers, and multiple detectors, we can explore multiple stars simultaneously, at different frequencies if we want. Furthermore, we can do this while our astronomy colleagues are mapping the sky for hydrogen gas, or large biogenic molecules, or other phenomena of scientific interest to them. This multiplexing potential is a new and exciting innovation that will speed up the SETI searching in the next decades.
Thus, while a new generation of SETI signal detectors called SonATA (SETI on the ATA) goes through its shakedown (a recent success in tracking the relatively nearby Rosetta spacecraft was a success), we can continue to do interesting radio astronomy with the same instrumentation. That’s a satisfying situation in the context of continuing debate about SETI methods and the best ways to optimize our chances for finding the signal of an extraterrestrial civilization. And it points to the growing maturity of the kind of interferometry used here, linking numerous small antennae on the impressive new hardware of the growing Allen site.
by Paul Gilster | Nov 10, 2008 | Culture and Society |
Larry Klaes sends along links to four of Fred Hoyle and Chandra Wickramasinghe’s books on panspermia, now available online. I first encountered the duo’s Evolution from Space shortly after its publication in 1981, found it curious and unlikely, and went on to other things. But the idea that a microbe might make its way between planets is under greater scrutiny than ever, even if the concept of interstellar panspermia remains contentious. And I think Larry sums the matter up nicely: “Certain ideas in these works have become a bit more accepted, or at least less further from the mainstream than when they first came out. They do make for very interesting reading whether you agree with their ideas or not.”
The Cosmic Ancestry site offers resources on the topic here, including PDF’s of Hoyle and Wickramasinghe’s Space Travelers: The Bringers of Life, Viruses from Space, Living Comets and Proofs That Life Is Cosmic.
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I’m looking at a stunning image of Saturn’s rings, with a huge, smoggy Titan bisected by their arc, and battered little Epimethus hovering just above the rings. The view is courtesy of the new National Geographic title Planetology: Unlocking the Secrets of the Solar System, capturing the intriguing organic chemistry of one Saturnian moon and contrasting it (via an insert) with another, the continually surprising Enceladus. The photograph is lovely, but Planetology aims to be more than a collection of memorable imagery. The method here is to look at the natural processes that shape the landscapes we see with our probes, with emphasis upon the forces that shape their existence. Earth appears in these pages not so much as our home but as another intriguing planetary surface.
Thus an image of Mercury’s Spider crater is contrasted with a shot from orbit of Canada’s Manicouagan crater, some sixty miles across, where rivers trace impact-generated fault lines even as weathering and crustal movement wear down other evidence of the cataclysmic event. The rift zones of Venus are contrasted with the long troughs of Mars’ Cerberus Fossae and insets of the Great Rift in East Africa. Page after page the views tell the tale of the movement of fluids on Titan and Mars, the action of ice volcanoes on Triton and the erupting plumes of Enceladus, the formation and movement of ice, the effects of storm and wind.
Astronaut and planetary scientist Tom Jones, working with planetary geologist Ellen Stofan, wrote the text, from which this:
Through field observation and experiment, earth scientists have built theories or hypotheses about how volcanoes erupt, earthquakes rumble, and glaciers advance and retreat. Today, researchers apply those models to the features seen on other planets; if those geological features can be explained by our model, then our understanding is reinforced. If solar system reality does not fit our Earth-generated theory, then the model needs revision. Geologists head back into the field for more data, and theorists go back to reassess their approach to explaining fundamental forces like impacts, volcanism, and erosion. By incorporating the data and imagery from robotic probes and astronaut expeditions into the study of our planet, we not only learn more about the solar system but also about our own Earth.
A point well taken. For me, the interesting thing about this book is the way it played with my sense of perspective, so that the unusual features we see on distant planets and moons relate to things I take for granted on this planet because I’m not used to looking at them from space. We’ll do that same kind of perspective-shifting one day when we gain the ability to image exoplanets up close, a distant prospect, but perhaps within reach in a matter of decades with extended versions of Webster Cash’s New Worlds and other space-based observatories.
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The latest Carnival of Space is up at Simostronomy, with special attention to the idea of magnetic shielding for future space travelers. Solar and cosmic radiation provide a danger great enough that an unfortunately timed solar storm would quickly prove lethal to humans and associated electronics. The Potentia Tenebras Repellendi site quotes Robert Bingham from the University of Strathclyde, one of the venues where this work is being conducted: “It would be a bit like being near the Hiroshima blast. Your skin would blister, hair and teeth fall out and before long your internal organs would fail. It is not a very nice way to go.”
Bingham’s team, as Universe Today notes, is working on a prototype that should be operational within five years, a mini-magnetosphere generator that can do for astronauts what Earth’s magnetosphere does for us on the ground, protecting our bodies from harm. The system is no bigger than a large desk and needs about as much energy as an electric kettle. It would operate through two small satellites, located outside the spaceship, which could be switched on if an approaching solar flare or coronal mass ejection were detected.
So now we have scaled the magnetic bubble idea down into an efficient deflector shield. Says Ian O’Neill at the Universe Today site:
This astounding achievement is a big step toward protecting sensitive electronics and the delicate human body against the radioactive effects of manned missions between the planets. It may sound like science fiction, but future astronauts may well shout the order to “RAISE SHIELDS!” if the Sun flares up during a 36 million mile journey to Mars…
More in this article from the Telegraph, which points out that although the idea of a magnetic bubble has been around since the 1960s, the thinking was that only a large bubble, perhaps 100 kilometers wide, could work. The energy involved in generating such a field would be enormous. The recent experiments, conducted not only at Strathclyde but at the Rutherford Appleton Laboratory and the University of York, makes it appear that a solution to the ‘space weather’ problem is on the horizon, at least until we hit the heliopause, beyond which all bets are off.
by Paul Gilster | Nov 7, 2008 | Outer Solar System |
The pace of change being what it is, adjusting our time frames can be a difficult task. That’s particularly true in the planning of space missions, where the gap between what we seem able to do and the actual window for doing it can become as large as it is frustrating. NASA and the European Space Agency, for example, will make a choice in 2009 between a Jupiter/Europa mission and a project called the Titan and Saturn System Mission (TSSM). Whichever is chosen, the projected launch date is at least twelve years away, with arrival expected no earlier than 2030. The lengthy interval is the inevitable result of the complexity of mission planning and the realities of orbital mechanics.
We’re always in a hurry about space missions because we’re so anxious for new information, but absent propulsion breakthroughs, we’re still tied to multi-decade planning cycles. Even so, as we investigate ways to fly missions faster, the prospect of what we might do with the Titan and Saturn mission looms large. An interesting article in Astrobiology Magazine looks at TSSM and notes its multiple objectives: To deploy an orbiting spacecraft around Titan, to explore its surface through a dedicated probe, and to examine its landscapes via a hot air balloon.
Image: An artist’s impression of the TSSM balloon airborne over Titan. Credit: European Space Agency.
This would be a tricky mission, one that recognizes, among other things, the challenges of a soft landscape that could trap a robotic rover. Current thinking is that a helicopter rotor could be used to move the surface probe from one location to another, or that it could be equipped with flotation devices in the event that a splashdown in a hydrocarbon lake is made the objective. The Huygens probe, for all its success, was not equipped to do surface science to any degree, so putting a probe into this terrain is needed to understand Titan’s surface chemistry.
A Titan orbiter, meanwhile, would substantially add to what Cassini has already done. Our views of Titan from the descending Huygens were spectacular, with liquid methane rivers winding down icy slopes amidst the hydrocarbon haze, but while Cassini has been able to peer through the atmosphere with radar, it’s unable to see large parts of the surface. Thus Athena Coustenis (Paris Observatory), who is involved in TSSM mission design:
“We need a Titan-dedicated orbiter because after four years of Cassini, we still haven’t mapped more than 25 percent of Titan’s surface. When you see the diversity the moon has, you realize it needs full-coverage mapping. And we can have a polar orbiter, whereas Cassini only passes by Titan on the ecliptic.”
The balloon concept is particularly intriguing. You may remember reading about a 1983 NASA workshop at which the idea of seeding the atmosphere of Titan with floating laboratories was discussed. A large balloon or powered blimp would move through the skies while dispersing smaller balloons to operate between ten and 100 kilometers above the surface. The TSSM concept is not quite so grand but seems more realistic, with a pared down mission scenario that builds upon our experience with Cassini and Huygens. The latest TSSM update has this to say:
We are now in the phase of describing our study of the past year for a return to Titan and the Saturnian System (TSSM) in extensive reports that will allow the science committees appointed by NASA and ESA agencies to evaluate the interest and feasibility of the mission. The Joint Science Definition Team (JSDT), and engineers have been working hard on putting together these reports and on defining the science, as well as the measurement requirements related to our ambitious mission, which comprises a dedicated Titan orbiter, and two in situ elements: a hot-air (Montgolfière) balloon and a Mare lander. The balloon is to fly over Titan’s mid latitudes at 10 km altitude for about 6 months, while a short-lived probe will land in a north-polar lake. The CNES French Agency has committed to supplying a large part of the balloon, and is actively studying the Montgolfière. For the lander, the flourishing heritage from Huygens is of great benefit to implementation of the mission as the orbiter heritage from Cassini.
Despite all our recent work, Titan remains in so many ways an enigma. Yes, we see geophysical processes that remind us of Earth, and a methane cycle that corresponds to the hydrological cycle on our own planet. Is there a form of volcanism on Titan involving water ice and ammonia? Is Titan’s climate stable or changing even as we study it? A free-ranging balloon could tell us so much about the processes at work here, while probe concepts ranging from a long-lived equatorial lander to a short-term probe destined for a northern lake would firm up our understanding of conditions at the surface. This is an ambitious mission whose progress through the funding minefield we’ll watch with interest.
by Paul Gilster | Nov 6, 2008 | Exoplanetary Science |
Roughly twenty percent of all detected exoplanets are in binary systems, intensifying our interest in Alpha Centauri. Recent work, however, has been less than encouraging to those hoping to find one or more terrestrial worlds around these stars. Indeed, Philippen Thébault (Stockholm Observatory), Francesco Marzari (University of Padova) and Hans Scholl (Observatoire de la Côte d’Azur) have shown that in the case of Centauri A, the zone beyond 0.5 AU is hostile to the accretion processes that allow planets to form. Any terrestrial-class world that close to Centauri A would be excluded from the habitable zone, a region thought to extend from 1.0 to 1.3 AU around the star.
The same team now goes to work on Centauri B, having pointed out in the earlier paper that the mathematical modeling it used there was unique to Centauri A and could not be applied indiscriminately to other systems, not even to the second star of the Centauri binary. The authors are targeting the phase of planetary formation when kilometer-sized planetesimals accrete, and examining the effect that perturbations and gas drag have on impact velocities within a test population of such planetesimals. As with Centauri A, the results show that this early formation stage can take place only in a region within 0.5 AU.
That just might allow the needed accretion and hence planet formation to occur within the innermost part of Centauri B’s habitable zone, which is estimated to extend from 0.5 to 0.9 AU. But even here the limits are tight, and the authors believe that because planetesimals in this region would have such high relative velocities (as opposed to a system unperturbed by the close binary Centauri A), planet growth would tend to occur much more slowly.
But let me quote the paper directly on this crucial matter:
Planetesimal accretion is marginally possible in the innermost parts, ?0.5 AU, of the estimated habitable zone. Beyond this point, high collision velocities, induced by the coupling between gas friction and secular perturbations, lead to destructive impacts. Moreover, even in the ? 0.5 AU region, ?v are increased compared to an unperturbed case. Thus, ”classical”, single-star like runaway accretion seems to be ruled out.
The case is strong — in order to arrive at the subsequent planet, you first have to let accretion go to work to build it, whether in or out of the habitable zone. This work does not, then, contradict other findings that planets are feasible within the habitable zones of the Centauri stars, but does insist that they are highly unlikely to form there. So are there other ways we could wind up with planets in the habitable zone?
Two possibilities remain: Changes in planetesimal orbits as gas within the early system is dispersed, and greater separation between the two stars early in their history, which would make perturbations less pronounced. Can either leave us hope for such worlds? The first seems dubious:
…we ?nd that later progressive gas dispersal reduces all ?v to values that might allow accreting impacts. However, we ?nd that the system has ?rst to undergo a long accretion-hostile transition period during which most of the smaller planetesimals are removed by inward drift and most bigger objects are probably fragmented into small debris. Thus, the positive effect on planetesimal accretion is probably limited.
As to a wider initial separation of the Centauri stars reducing the perturbation effects, much work remains to be done. The minimum separation for accretion processes to prove favorable to the formation of a planet in the habitable zone seems to be 37 AU. Could the Centauri stars have once been separated by this amount or greater? Finding the answer to that question depends upon working out the likelihood of orbital changes in early open clusters. In short, we don’t know.
Thébault, Marzari and Scholl are doing significant work, examining as they do the crucial early stages of planet formation, and the authors point out that the even earlier phases, when the kilometer-sized planetesimals are themselves forming, have not yet been modeled. Right now we can hold out hope for the region 0.5 AU or so around Centauri B, but it is chastening to reflect that this narrow region may offer the only realistic prospect for a habitable world in this nearby system.
The paper is Thébault et al., “Planet formation in the habitable zone of alpha Centauri B,” accepted for publication in Monthly Notices of the Royal Astronomical Society and available online. Thanks to andy for the pointer.
by Paul Gilster | Nov 5, 2008 | Astrobiology and SETI |
The Moon is, for obvious reasons, rarely considered an interesting venue for astrobiology. But I’ve been looking through Joop Houtkooper’s presentation at the European Planetary Science Congress, noting his contention that some lunar craters might hold samples of life from the early Earth, and perhaps even from Mars. If the name Houtkooper rings a bell, it may stem from the splash he made last year by suggesting that the Viking probes to Mars may have discovered Martian microbes consisting of fifty percent water and fifty percent hydrogen peroxide.
Although some extremophiles here on Earth put hydrogen peroxide to use, the theory is quite a long shot. But then, Houtkooper (University of Giessen, Germany) seems to thrive on remote possibilities. His lunar theory works like this: Certain craters on the Moon are effectively shielded from sunlight, at least deep within their recesses. Shackleton crater at the south pole is a case in point, a place that may contain sub-craters free of even reflected light from the crater edges. These ultra-cold places might preserve any life that found its way there.
Ancient meteorites would be the source of that life, debris blasted off a primordial Earth by various impacts. It is even conceivable, though at the outer edges of possibility, that we might find viable microbes that have survived the intervening eons in a dormant state. Let me quote from an abstract of Houtkooper’s talk that is available online:
Some of this biogenic material would have likely been preserved on the Moon, probably frozen into the regolith and later being covered by lunar dust. Some of its microbial load, dislodged with rocks from Earth, might have survived the transport to the Moon, and would have possibly remained in a viable state if buried quickly under the radiation reworked surface. Some of these organisms may have even landed in lunar locations, where liquid water was present for a temporary period. These pockets of water would have been small in extent, possibly microscopic, within an excavated impact crater. Perhaps, these impact zones would have provided suitable conditions to support a highly localized biosphere for a limited period of time. Given the dryness of the Moon, its lack of a substantial atmosphere and lack of dynamic activity, we consider it unlikely that any surviving microbes would still be active on the Moon, but it is not entirely impossible if liquid would be found beneath the lunar ice in some locations. More likely, however, is that these temporarily existing liquid water pools froze and may still hold viable microbial organisms, possible even organisms that extended their life time for a short while on the Moon.
Houtkooper is suggesting that a large enough impact could create a temporary and vanishingly thin lunar atmosphere that conceivably could call dormant life back into action. Life on the Moon. The odds seem astronomical, but the chance to study ancient microbes from our planet’s earliest history, and perhaps microbes from Mars as well, would make this an investigation worth pursuing if we were in the vicinity anyway. The search for lunar ice at the bottom of such craters could make this a possibility for future manned missions. See also this piece in Astrobiology Magazine on earlier work by John Armstrong, Ian Crawford and Emily Baldwin on the survival of biological markers from Earth on the Moon.
