by Paul Gilster | Sep 13, 2005 | Astrobiology and SETI |
Space artist Jon Lomberg, whose work illustrated yesterday’s entry on the white dwarf star GD 362, wrote recently with a comment on Centauri Dreams‘ September 8 story on Titan. The story discussed new theories on Titan as an abode for life, citing a presentation at the recent Division of Planetary Sciences meeting in Cambridge and quoting Southwest Research Institute scientist David Grinspoon on the possibilities inherent in Titan’s abundant hydrocarbons and acetylene, which might help power a metabolism.
Titan, of course, is a very cold place, which would seem to inhibit the needed chemistry. But Lomberg points out a way around the problem:
“Consider the organic superconductor dimethyltetra-thiofulvalene tetracyano-quinodimethane. Discovered in the 1970s, this was the first organic superconductor found, and it remains superconductive at [relatively] high temperatures. More have been discovered since. When Carl Sagan and I were working on my Encyclopedia Galactica series of paintings, he liked my speculation that such substances might provide a way to circumvent the slow pace of low-temperature chemical reactions. We were thinking specifically of planets around cool stars, but certainly Titan is a closer candidate worth considering in this regard. Carl suggested changing the …..quinodimethane to….quinodimethanic acid and listing it as the genetic base for low temperature organisms…”
Organic superconductors as a way around the low temperature problem — ingenious! You can find a description of a civilization based on such chemistry on p. 313 of COSMOS (I’m using the Random House 1980 hardcover edition, but later editions follow this pagination). The summary, written by both Sagan and Lomberg, is a hypothetical entry from the Encyclopedia Galactica that Sagan speculated might one day become available through interstellar radio contact.
As for the Encyclopedia itself, ponder as Sagan did what might be found in a radio message from another star. Perhaps its contents will be something like a palimpsest, whereon ancient writers reused papyrus by writing new material over old. A primer teaching the language of interstellar discourse could surround the real message. “Radio technology permits that message to be inconceivably rich,” Sagan writes. “Perhaps when we tuned in, we would find ourselves in the midst of Volume 3,267 of the Encyclopedia Galactica.” (p. 314).
And as Sagan goes on to say:
“…with our newly acquired information sorted into a computer memory, we would be able to see which sort of civilization lived where in the Galaxy. Imagine a huge galactic computer, a repository, more or less up-to-date, of information on the nature and activities of all the civilizations in the Milky Way Galaxy, a great library of life in the Cosmos. Perhaps among the contents of the Encyclopedia Galactica will be a set of summaries of such civilizations, the information enigmatic, evocative — even after we succeed in translating it.”
It’s a long way from Titan to a galactic civilization, but living processes there would imply that life takes hold in remarkably varied environments. Some introductory information on organic superconductors can be found here. A sample of Lomberg’s Encyclopedia Galactica paintings can be found at his Web site.
by Paul Gilster | Sep 12, 2005 | Deep Sky Astronomy & Telescopes, Exoplanetary Science |
The white dwarf star GD 362 has been cooling for up to five billion years. You might think of it as an image of our Sun’s future, although it was originally about seven times more massive. As the Sun’s will do five billion years from now, this star’s core simply ran out of fuel, reaching a point where it could no longer create the heat needed to counterbalance gravity. As the star died, it would have given off stellar material, initially swelling dramatically, then dying back to the dwarf we see today.
But what has astronomers studying Gemini Observatory data talking is that GD 362 seems to be surrounded by an extensive band of dust and debris. The find is striking — gravity and radiation should long ago have removed such materials from the star’s proximity. The only reasonable explanation is that an asteroid, or perhaps something as large as a planet, has survived the demise of the star and is now contributing material for the debris disk. “The parallel to our own solar system’s eventual demise,” says Eric Becklin, UCLA astronomer and Principal Investigator for the Gemini observations, “is chilling.”
Image: Artist’s visualization of what a dust disk might look like around the white dwarf GD 362. A more distant planet (shown at upper left) might be responsible for “shepherding” the dust ring and promoting ongoing collisions. This striking image (click to enlarge) is the work of noted space artist Jon Lomberg (www.jonlomberg.com).
From a Gemini Observatory news release:
“There are just precious few scenarios that can explain so much dust around an ancient star like this,” said UCLA’s Mike Jura, who led the effort to model the dust environment around the star. “We estimate that GD 362 has been cooling now for as long as five billion years since the star’s death-throes began and in that time any dust should have been entirely eliminated.” Jura likens the disk to the familiar rings of Saturn and thinks that the dust around GD 362 could be the consequence of the relatively recent gravitational destruction of a large “parent body” that got too close to the dead star.
And GD 362 raises other mysteries. Perhaps most surprising is the abundance of metals — calcium, magnesium and iron at levels similar to our own Sun — where no heavier elements would have been expected. UCLA’s Benjamin Zuckerman, a co-author on the Gemini-based paper that will appear in an upcoming issue of the Astrophysical Journal, calls the finding “a complete surprise.” You can hear audio clips of Zuckerman discussing the star by following links on this page.
An independent team working with the NASA Infrared Telescope Facility (IRTF) has produced data that support the idea of a dust disk around GD 362. And note this comment by University of Texas grad student Mukremin Kilic, who led the team making the IRTF observations. Here he makes reference to the only other white dwarf known to have a dust disk:
“Both of these stars’ atmospheres are continuously polluted by metals — that is, heavy chemical elements — almost surely accreted from the disk,” Kilic said. “If the accretion from a debris disk can explain the amounts of heavy elements we find in white dwarfs, it would mean that metal-rich white dwarfs — and this is fully 25% of all white dwarfs — may have debris disks, and therefore planetary systems, around them. Planetary systems may be more numerous than we thought.” More on the IRTF work can be found here.
by Paul Gilster | Sep 10, 2005 | Astrobiology and SETI, Outer Solar System
How long would it take to get to Alpha Centauri using a solar sail? The fastest travel time I’ve seen calculated is 1000 years. Imagine a reflective sheet only nanometers in thickness attached to the payload with diamond strength cable. A close pass by the Sun (the classic ‘Sun-diver’ maneuver, first called this, as far as I know, by Gregory Benford) is followed by sail deployment as close to the Sun as possible. Assume a sail of perhaps 100 kilometers in diameter, a payload of several million kilograms, and accelerations of a few g. After acceleration, the sail would be wound around the habitat for cosmic ray detection, and later re-deployment for deceleration.
Gregory Matloff presents these ideas in an essay with the fetching title “The Reenchantment of the Solar System: A Proposed Search for Local ET’s,” available online (thanks to Larry Klaes for the tip on this). As you can see from the title, the sail mission to Centauri is only the beginning of the possible wonders discussed here. For Matloff goes on to show that an advanced civilization whose star is leaving the main sequence could use identical techniques to reach much higher speeds. Replace the Sun with a giant star a thousand times more luminous and you cut travel time to Centauri down to about 320 years.
And while Centauri Dreams has often considered possible targets for interstellar probes, Matloff turns the story around. His paper discusses stars in the solar neighborhood that might be home to migrating interstellar civilizations. To fit the bill, the stars need to be subgiant or giant class, like Procyon (11.3 light years from the Sun), Beta Hydri (21.3 light years) or Pollux (35 light years). Could such stars have produced interstellar arks that might have reached the vicinity of our Sun? If so, wouldn’t the logical place to look for them be in the outer Solar System?
From the paper:
If we are indeed within such a “Dyson Sphere” of artificial worldlets, we could detect their presence through astronomical means since a space habitat will emit more infrared radiation than a like-sized comet or asteroid. Interestingly, several Kuiper-Belt objects have recently been found to have an unexpected and substantial red excess. It is argued that, in opposition to the assumptions of current SETI searches, the very advanced occupants of this possible local Dyson Sphere may have as little interest in beaming radio signals in our direction as we do in communicating with termites. A research program is proposed whereby large and small college observatories would routinely monitor the spectral irradiances of Near Earth and Kuiper Belt objects while a concurrent theoretical effort models the spectral characteristics of various proposed space habitats.
This paper, a winner in the National Institute for Discovery Science essay competition, is nicely followed up by Matloff’s recent work in the Journal of the British Interplanetary Society, including specifics on how to study hypothetical Kuiper Belt Objects of artificial origin. The author’s The Starflight Handbook (New York, John Wiley & Sons, 1989) remains an essential book for students of interstellar flight.
by Paul Gilster | Sep 9, 2005 | Outer Solar System
“Santa,” “Easterbunny,” and “Xena” may be odd names, but they beat the official designations given these objects by the International Astronomical Union — 2003 EL61, 2005 FY9, and 2003 UB313. All three are Kuiper Belt Objects (KBOs) discovered with the 48-inch Samuel Oschin Telescope at Palomar Observatory. The last of the three is the now famous 10th planet, but the other two KBOs are close to Pluto-size themselves, and like that world, are in elliptical orbits that take them out of the plane of the Solar System.
Did we say ’10th planet?’ Centauri Dreams realizes the designation is controversial, especially at the IAU, but cannot resist the urge to editorialize (if only obliquely) on behalf of a planetary designation for Xena. The rule seems simple: Pluto-size and up means planet.
So how do such orbits happen? Mike Brown, a professor of planetary astronomy at Caltech and leader of the discovery team, says these exotic objects may have actually formed in a much warmer environment. “We think that these orbital characteristics may mean that they were all formed closer to the sun, and then were tossed around by the giant planets before they ended up with the odd orbits they currently have,” Brown said.
We’ve discussed Xena before, but much remains to be said about its size. For we don’t know how reflective its surface is — assume a completely reflective, mirrored surface and you get an object that, at Xena’s current 97 AU from the Sun, would be about the size of Pluto. Kuiper Belt Objects are not, of course, perfect reflectors, and that implies Xena is actually larger than Pluto. It will take data from the Spitzer Space Telescope, gathered in late August, and the 30-meter IRAM instrument in Spain to help confirm Xena’s size. Spitzer’s infrared observations should help establish an upper limit.
Of the other two objects, Santa is the more curious. It seems to be cigar-shaped, with the longer axis of its body being about the diameter of Pluto in length. Moreover, Santa rotates in four hours, the fastest rotation of any large body in the Solar System. A tiny moon, nicknamed Rudolph, circles Santa every 49 days.
Easterbunny, like Santa some 52 AU from the Sun at present, is also about 3/4 the size of Pluto, and like that planet (and Xena as well) seems to be covered in frozen methane. For more, check Brown’s active and interesting Web site. A California Institute of Technology press release is here.
by Paul Gilster | Sep 8, 2005 | Astrobiology and SETI, Missions, Outer Solar System
Can there be livable habitats on Titan? A paper just presented at the Division for Planetary Sciences meeting in Cambridge makes the case that several key ingredients of life may be present on the huge moon. Titan possesses liquid reservoirs, organic molecules and the needed energy sources. The question: is the environment simply too cold? With temperatures down to -178 degrees Celsius (-289 degrees Fahrenheit), the chemical reactions to produce life would move ponderously, but perhaps not too slowly to function.
The first images from beneath Titan’s cloud cover made the speculation all the more intense. Methane shows up in clouds as well as in liquid form at the surface at these temperatures, and may provide the analog for Earth’s water in a life-sustaining hydrological cycle. Moreover, there are hints of ice volcanoes that imply the existence of large amounts of water (mixing with ammonia) not far below the surface.
So where does it all lead? From a Southwest Research Institute (San Antonio, TX) news release:
“One promising location for habitability may be hot springs in contact with hydrocarbon reservoirs,” says lead author David H. Grinspoon, a staff scientist in the SwRI Space Science and Engineering Division. “There is no shortage of energy sources [food] because energy-rich hydrocarbons are constantly being manufactured in the upper atmosphere, by the action of sunlight on methane, and falling to the surface.”
The team focuses on acetylene, which could be used by organisms in reaction with hydrogen to release the energy that could power a metabolism. That this is speculative is obvious, but if you’re looking for bizarre forms of life, consider Grinspoon’s other comment:
“The energy released could even be used by organisms to heat their surroundings, helping them to create their own liquid cryoenvironments,” says Grinspoon. “In environments that are energy-rich but liquid-poor, like the near-surface of Titan, natural selection may favor organisms that use their metabolic heat to melt their own watering holes.”
Centauri Dreams‘ take: It has always been natural to look for life in more or less terrestrial terms, but the recent study of extreme environments is showing us even on Earth how wide the parameters for life may be. It’s fascinating to realize that we now must include the satellites of outer planets, like Jupiter’s Europa, Ganymede and Callisto, along with Titan and even poor, battered Enceladus in the list of possibilities. Hard to imagine, but who knows what we may someday find on places as exotic as Triton.
Image: This processed image from Cassini’s Aug. 22, 2005, flyby of Titan reveals mid-latitudes on the moon’s Saturn-facing side. Is it conceivable that a living ecosystem may exist at the moon’s frigid temperatures? Credit: NASA/JPL/Space Science Institute.
And if we do start finding such life forms, it’s going to give a huge impetus to the belief that life is all but ubiquitous in the universe. Whether or not any significant percentage of it is intelligent is another question (Centauri Dreams leaves for philosophers the attempt to define ‘intelligence’). But a galaxy crowded with living worlds is a vision that awaits only the first confirmed sightings of terrestrial planets to go front and center. We should have such sightings within a decade, if not less. Keep your eye on the Kepler mission.
The paper “Possible Niches for Extant Life on Titan in Light of Cassini-Huygens Results” was presented today at the Division for Planetary Sciences meeting in Cambridge.
