by Paul Gilster | Sep 26, 2005 | Astrobiology and SETI, Outer Solar System
Centauri Dreams recently looked at Titan as a possible abode for life, energized by a paper given at the Division of Planetary Sciences meeting by David Grinspoon. A researcher at the Southwest Research Institute (Boulder, CO), Grinspoon is also an author whose book Lonely Planets: The Natural Philosophy of Alien Life (New York: Harper, 2004) discusses in depth and style the issue of extraterrestrial life and where we might find it. His Web site offers numerous links to his scientific output and materials from his book.
Grinspoon has been all over the news lately, as witness this interview in the online journal Astrobiology Magazine. Recently, he was kind enough to forward a copy of his DPS paper “Biologically Enhanced Energy and Carbon Cycling on Titan?” Centauri Dreams reads a lot of research papers, but Grinspoon’s work stands out not only for its rigor but its sheer energy. He speculates, for example, that our model of miniaturized cellular life in water on Earth may be misleading as a model for life elsewhere. Titan could involve “…huge (by Earth standards) and very slowly metabolizing cells…”
Image: As Cassini approached Titan on Aug. 21, 2005, it captured this natural color view of the moon’s orange, global smog. Could there be life beneath the haze? Credit: NASA/JPL/Space Science Institute.
Another intriguing notion: biological heating could contribute to the smoothness and surface activity on Titan, contributing to melting of water-ammonia ice. “There may be places on Titan that are energy-rich but liquid-poor, with plenty of acetylene to metabolize, though it may be locked up in ice. In such a case, evolution would favor organisms that could use this energy to melt their own little watering holes.”
The key issue faced by proponents of life on Titan is energy — what could sustain a metabolism on or near the frigid surface? Grinspoon can suggest an answer. In Titan’s upper atmosphere, methane is being turned into other molecules, among them acetylene, which condenses and falls to the surface. Such acetylene could turn back into methane by reacting with hydrogen gas; quite a bit of energy would result. From the paper:
“Because of acetylene’s higher specific gravity, solid acetylene may be present at the bottom of the ethane-methane reservoirs and available as an energy source for various chemical reactions that involve a multitude of organic compounds. The dearth of obvious impact features in early high-resolution Cassini imagery…and inferred youth of the surface imply the possibility of active resurfacing and possible burial or subduction mechanisms that could supply subsurface liquid reservoirs with acetylene and other photochemical products.”
The paper “Biologically Enhanced Energy and Carbon Cycling on Titan?” appears in Astrobiology Vol. 5, No. 4 (Nov, 2005), pp. 560-567; particularly noteworthy is its list of search parameters for possible life on Titan. Grinspoon notes in an e-mail message that he is now working on thermal modeling of idealized Titan organisms and the possibilities of their channeling waste heat into the environment, but this work is still in its preliminary stages.
by Paul Gilster | Sep 24, 2005 | Deep Sky Astronomy & Telescopes, Research Tools |
Does quantum mechanics determine what we see in the large-scale structure of the universe today? Centauri Dreams admits to finding the notion nonsensical until reading Brian Greene’s fine Fabric of the Cosmos (New York: Knopf, 2004), which explained the connection between the very small and what may exist on the macroscopic scale through the mechanism of cosmic inflation. In any case, it’s a fascinating thought that we may one day understand the earliest moments of the universe by applying quantum principles that might be observable in the large scale structures of the cosmos.
Physicist Raja Guhathakurta (University of California) has a go at issues like these in a presentation called “The Milky Way, Schrodinger’s Cat and You,” which was delivered as the September Keck Astronomy lecture. It’s a sign of the riches available through the digital world that we can now download Dr. Guhathakurta’s lecture through the kind offices of W. M. Keck Observatory in Mauna Kea (HI). Click here for the download, and ponder not only how helpful Keck’s outreach is but how much a note to the Observatory would encourage further efforts along these lines. Well done, Keck!
In addition to the Keck lecture, the latest listening in these parts has been the Feynman Lectures on Physics, available through Audible.com and consisting of audio recorded early in the 1960’s at the California Institute of Technology. For that matter, Centauri Dreams got acquainted with Greene’s Fabric of the Cosmos on audio from the same source, a reminder that the resources available for self-education have never been more numerous. We need to encourage other institutions to distribute class lectures, conference proceedings and other quality material in easily downloadable format.
by Paul Gilster | Sep 23, 2005 | Exoplanetary Science
We’ve developed many techniques for planetary detection since the first discovery of a planet orbiting a main sequence star in 1995, but a recent addition to the repetoire is looking in systems already known to have planets. By studying stars that display a transiting planet — a planet moving in front of the star as seen from Earth — any variation in time between the transits can be detected. From that data, information about any unseen planet perturbing the transits can be inferred.
The new method is called TTV, for ‘transiting timing variations,’ and here’s the most exciting thing about it: a planet comparable to the size of Earth should be detectable using these methods, giving TTV a sensitivity in advance of any other current detection method. And we do expect to find many a multi-planet system out there, with data that can provide insights into the formation of our own Solar System. But to use the method we have to discover and monitor transiting planets.
All of this is summarized in a new paper by Jason H. Steffen and Eric Algol, physicists at the University of Washington. Their work focuses on the TrES-1 planetary system discovered in 2004, and reports on their search for a possible perturbing planet in that system. Found through the efforts of the Trans-Atlantic Exoplanet Survey (TrES), TrES-1 is roughly 500 light years from the Sun in the constellation Lyra. Although Steffen and Algol could find no convincing evidence for a second planet in the system, they were nonetheless able to place constraints on any planet that might be there.
From the paper:
It is unclear what fraction of probable planetary companions are excluded by our results….The sensitivity of TTV to the mass of a perturbing planet renders it ideal for discovering and constraining the presence of additional planets in transiting systems like TrES-1. These studies can help determine the ubiquity of multiple planet systems and resonant systems-including the distribution of mass in those systems. Moreover, TTV analyses of several systems can play a role in identifying the importance of various planet-formation mechanisms. For example, the presence of close-in terrestrial planets favors a sequential-accretion model of planet formation over a gravitational instability model…
So the TrES-1 system may or may not include other planets than the one already detected, but Steffen and Algol argue that TTV methods applied to higher precision observations should be able to create a more detailed map of such systems. TTV thus emerges as another tool in the planet hunter arsenal, complementing radial velocity, planetary microlensing and planetary transit detections. It may be taking us one step closer to the first terrestrial planet ever found orbiting another star.
The paper is Steffen, J. and E. Algol, ” An analysis of the transit times of TrES-1b,” available at the arXiv site via the above link.
by Paul Gilster | Sep 22, 2005 | Outer Solar System
As a boy, I recall paging through an old, nine-volume encyclopedia we kept on a livingroom shelf. Published some time in the 1920s, it was hopelessly out of date from a science standpoint, and I remember reading its entry on the planets and feeling, with the smug certainty of youth, that my modern world (this was the late 1950s) had now figured out most of the puzzles still unsolved by the editors. The editors, after all, hadn’t known about Pluto, but we did, and Pluto’s discovery surely meant that the mapping of the Solar System was complete.
Youthful smugness has a way of being brought up short by events, and so do astronomical depictions of things we’ve seen imperfectly. Today we know that Pluto itself is one of what may be a vast number of ‘ice dwarfs,’ a kind of planet probably numerous in the Kuiper Belt. Sedna and Quaoar are members of this class, as is, evidently, Neptune’s moon Triton and the newly discovered 10th planet, still known officially as 2003 UB313. Indeed, according to Alan Stern, principal investigator for the New Horizons Pluto mission, we’ve only catalogued about 2 percent of the Kuiper Belt and have already found over a thousand of these remote objects in their distant elliptical orbits.
Stern, who checks in every month at the New Horizons Web site with thoughts on the mission’s progress, paints a picture of planetary formation that’s a long way from what showed up in my ancient blue encyclopedia. As the giant planets formed, hundreds to thousands of smaller worlds also emerged, some Pluto sized, some larger than Earth. Most of these dwarf planets were ejected into much more distant orbits as the gas worlds cleared out their formation zones some four billion years ago.
Image: The New Horizons spacecraft during its encounter with Pluto and Charon. Scientists hope the spacecraft will make at least one flyby of a Kuiper Belt object beyond Pluto’s orbit. Credit: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI).
Consider the clues: Pluto’s moon Charon was evidently formed from an impact with an object nearly as large as Pluto itself. Triton circles Neptune in a retrograde orbit that indicates gravitational capture, an ice dwarf that avoided ejection into the outer system. Uranus and Neptune both exhibit pronounced polar tilts, the mark of collisions with Earth-sized bodies and up. Stern believes that for such collisions to have occurred, as many as a few dozen Earth-sized worlds must once have populated the outer regions of the Solar System.
Thus an entirely new paradigm emerges. Here’s Stern:
Less than two centuries ago it was discovered that all the stars one can see by eye, and their innumerable brethren seen by telescope, are distant Suns, with numbers too great to count. Similarly, it was just under a century ago that our galaxy, the Milky Way, was realized to be but one of literally billions of galaxies. Both of these realizations, like the 16th century realization that the Sun (not Earth!) is the center of our solar system, jarred perceptions and changed textbooks in revolutionary ways. Just as jarring to us now is the newly emerging view that our solar system made, and is still littered with, very many distant planets, most of which are nothing like the familiar planets that orbit close to the Sun, like Earth. In a real sense, we are seeing a new chapter unfold in the revolution that Copernicus wrought when he displaced the Earth from the center of everything.
So the strange worlds in their distant, highly elliptical orbits seem to be the norm, and the well-ordered Solar System we all grew up with gives way to a planetary system that may extend out a thousand times farther than Pluto. All of which is ample material for the New Horizons mission as it pushes past Pluto into the Kuiper Belt, and a salutary reminder that just when we start to feel confident, even comfortable in our worldview, new data may just turn everything upside down.
Stern’s most recent “PI’s Perspective” column is here.
by Paul Gilster | Sep 21, 2005 | Autonomy and Robotics
New technologies, rarely foreseen by ‘futurists,’ often change everything. Just as science fiction could not predict the PC, so visionaries like Arthur C. Clarke could not predict the developments in electronics that would make his idea of geostationary relay satellites practicable. Yes, Clarke dreamed up the idea of such satellites, but he was talking about manned space stations handling the abundant telecommunications traffic that was to come. In a mere 15 years, it would become possible for radio technology to bring Clarke’s ideas to fruition, just as Earth observation, astronomy and military reconaissance would be performed by unmanned satellites.
Now we speculate about proposed manned expeditions to Mars, but is the future human or robotic as we push into the outer Solar System? Bob Parkinson tackles the subject in an essay in the March/April issue of the Journal of the British Interplanetary Society. Consider the march of machinery in the years since the first manned spacecraft. People are still in low Earth orbit (other than the still unduplicated Moon landings), but every planet except Pluto has been studied by robotic probes, and the New Horizons mission will leave for Pluto as early as this January.
Cassini has been triumphant in its still unfolding tour of Saturn space, we’ve touched down robotically on Venus, Mars and Titan, not to mention NEAR’s asteroid landing, and we’ve banged an impactor into an onrushing comet. It’s important to realize, Parkinson writes, that these are not just scouting missions for future human flights, but contributions to our knowledge in their own right, and perhaps a model for what is to come.
I can think of a variety of reasons why manned Mars missions will be tricky (and Parkinson lists them all, from dealing with zero-g over long flight times to radiation exposure hazards and problems of long-term, closed-cycle life support). Even so, he’s not arguing that men will never set foot on Mars as much as noting the reasons why robotics can help and sometimes take precedence over humans. Consider the possibility of life on Mars — if we find it via robotic rover, can we land people on the planet without contaminating it? Are our rapidly improving rovers capable of answering such questions without putting human crews on the surface?
And consider this intriguing virtual reality notion:
In 1997 the author suggested that if Mars was mapped down to very high resolution, it might be possible to create a ‘virtual Mars’ through which tourists could wander as they chose. Rather than using this data for science alone, direct access would allow ordinary people to actually see for the first time sights that had never been seen before by human eyes.
25 years ago, the issue of man vs. machine in outer space would not have had the resonance it has today. Parkinson concludes with a thought on funding and commitment:
Robotic exploration missions continue to be justified on the basis of their scientific value, and as a consequence compete for funding with other science programmes — not always successfully. The implication is that we must learn to find arguments which parallel those used by advocates of human spaceflight, which emphasize the adventure, heroism and (vicarious) participation aspects of exploration. Then the exploration (and exploitation) of the Solar System can become a joint carbon-silicon enterprise.
The paper is Parkinson, “The carbon or silicon colonization of the universe?” JBIS 58 (March/April 2005), pp. 111-116. Centauri Dreams hereby reiterates its lament that JBIS is unavailable in full-text form even on the major scientific databases, making a nearby research library all but essential unless you’re a subscriber.
