by Paul Gilster | Nov 14, 2006 | Astrobiology and SETI |
Astrobiology, the study of life as a planetary phenomenon, aims to understand the fundamental nature of life on Earth and the possibility of life elsewhere. To achieve this goal, astrobiologists have initiated unprecedented communication among the disciplines of astronomy, biology, chemistry, and geology. Astrobiologists also use insights from information and systems theory to evaluate how those disciplines function and interact. The fundamental questions of what “life” means and how it arose have brought in broad philosophical concerns, while the practical limits of space exploration have meant that engineering plays an important role as well.
So goes the introduction to the Astrobiology Primer now available as a reference tool for those trying to acquire the fundamentals of this multidisciplinary subject. Ninety researchers contributed insights and information to the collaborative effort. The work ranges through stellar formation and evolution, planet detection and characterization to the evolution of life through time, and it’s hard to imagine a better way to bone up on the basics. An exotic specialty now, astrobiology will gradually become one of our most significant disciplines as we continue to find and examine the worlds that fill the galaxy in their millions.
by Paul Gilster | Nov 14, 2006 | Astrobiology and SETI |
Where did our planet get the stuff from which life is made? The sources seem surprisingly diverse, and we’re learning more about how organic materials may have complemented each other in forming life four billion years ago. Extraterrestrial compounds — biomolecules formed in deep space and falling to Earth — probably contributed. And so did lightning and ultraviolet radiation, along with vulcanism and deep water chemical reactions that could enhance molecular synthesis.
Now getting new emphasis is the role of mineral surfaces in helping to activate molecules essential to life, like amino acids (from which proteins are made) and nucleic acids (think DNA). In a recent study, Robert Hazen (Carnegie Institution Geophysical Laboratory) described where we stand at identifying the pairing of molecule and mineral. When molecules like amino acids adhere to mineral surfaces, a variety of organic reactions can occur that affect what life can emerge.
“Some 20 different amino acids form life-essential proteins,” Hazen explained. “In a quirk of nature, amino acids come in two mirror-image forms, dubbed left and right-handed, or chiral molecules. Life, it turns out, uses the left-handed varieties almost exclusively. Non-biological processes, however, do not usually distinguish between left and right variants. For a transition to occur between the chemical and biological eras, some process had to separate and concentrate the left- and right-handed amino acids. This step, called chiral selection, is crucial to forming the molecules of life.”
The hunt, then, is to find what mineral surfaces are what Hazen calls the best ‘docking stations’ for various biomolecules. The possibilities are vast considering the number of mineral types and available molecules, but Hazen’s team is using DNA microarray technology to help. The result is to overhaul the protocols for doing this work and make the investigation both more accurate and much faster. The technique allows the team to study these complex interactions and discover which mineral surfaces and which organic molecules manage to work together.
Much work lies ahead, but Hazen’s team can now identify a million types of biomolecules through their interactions with mineral surfaces, and analyze the results quickly. The goal is an understanding of how specific organics from the vast number available assembled into early life, and how they were able to become concentrated enough to begin a basic metabolism. The work, which draws on biology, chemistry and geology, gives us a glimpse not only of the primitive Earth but a better understanding of the conditions that may lead to life on other worlds.
The paper is Hazen, “Mineral surfaces and the prebiotic selection and organization of biomolecules,” American Mineralogist Vol. 91, No. 11-12 (November, 2006), pp. 1715-1729.
by Paul Gilster | Nov 13, 2006 | Astrobiology and SETI |
An interesting story on Seth Shostak’s recent appearances in Athens, OH ran today in The Athens News. In a pair of talks Shostak, senior astronomer for the SETI Institute (Mountain View, CA), explained to a general audience why he thinks extraterrestrial life is out there. He even gave a timeline for its discovery: within the next two dozen years (he went on to bet each member of the audience a cup of Starbuck’s coffee on the proposition). Each SETI experiment, Shostak added, gathers more data than all the previous ones combined.
Deep in the article are two Shostak suggestions for extending the SETI search. First, focus on the same area of sky for longer periods of time, instead of today’s common practice of looking at a star for a few minutes and then moving on. Keep a longer gaze and look for signals of short duration that may repeat every few hours or days.
The second tactic: work harder on binary systems. These may contain technological civilizations that have explored both sides of their twin solar systems (inevitably, Centauri A and B come to mind). If two members of a binary system line up properly from our vantage point — and if the two systems are talking to each other — then there is a possibility for detecting their powerful, tightly focused communications.
Centauri Dreams‘ take: Believing that technological civilizations are rare in our galaxy (and elsewhere, for that matter), I doubt either of these strategies will succeed. But I’m all for SETI proponents who say we won’t know until we try. If ever there was an argument I would be happy to lose, it’s this one, but I’ll let someone else take Shostak up on that two dozen year bet.
by Paul Gilster | Nov 13, 2006 | Communications and Navigation
Given how tricky it is to pick up accidental radio signals — “leakage” — from extraterrestrial civilizations, how hard would it be to communicate with our own probes once they’ve reached a system like Alpha Centauri? A front-runner for interstellar communications is the laser. JPL’s James Lesh analyzed the problem in a 1996 paper, concluding that a 20-watt laser system with a 3-meter telescope as the transmitting aperture could beam back all necessary data to Earth. It’s a system feasible right now.
Right now, that is, if we had some way to get the telescope, just a bit larger than the Hubble instrument, into Centauri space. But even though propulsion lags well behind laser technology for such a mission, we’re continuing to study how lasers can help closer to home. Their high frequencies allow far more data to be packed into the signal, but the highly focused beam also uses a fraction of the power of radio. Data return becomes less of a trickle and more of a flood (imagine high-definition moving video from Mars).
How to handle atmospheric effects that can hamper Earth-based receivers? It’s a problem even on cloud-free days because dust, dirt and water vapor can still scatter light and deflect parts of the beam. Listen to Penn State’s Mohsen Kavehrad: “Free space optical communications offer enormous data rates but operate much more at the mercy of the environment…All of the laser beam photons travel at the speed of light, but different paths make them arrive at different times.”
The result: data ‘echoes’ that confound accurate reception. But the project Kavehrad is working on, funded through the Defense Advanced Research Agency, aims at achieving almost 3 gigabytes per second of data over a distance of 6 to 8 miles through the atmosphere. What the Penn State team has done is to bring digital signal processing methods to bear on laser communications to make the optical link more reliable. They call their approach free-space optical communications. Here’s how a Penn State news release describes the system’s operation:
Using a computer simulation called the atmospheric channel model developed by Penn State’s CICTR, the researchers first process the signal to shorten the overlapping data and reduce the number of overlaps. Then the system processes the remaining signal, picking out parts of the signal to make a whole and eliminate the remaining echoes. This process must be continuous with overlap shortening and then filtering so that a high-quality, fiber optic caliber message arrives at the destination. All this, while one or both of the sender and receiver are moving.
The system works both for air-to-air and air-to-ground links, and provides fiber-optic quality signals. But extend the premise to the growing needs of the Deep Space Network to relieve spectrum overcrowding and provide reliable high-bandwidth links to spacecraft around the Solar System. We’re moving toward a future model of networked space vehicles, communicating not only with Earth but also with each other to coordinate data transfers that will one day be optical.
The bright future of optical communications relies on resolving complications like atmospheric distortion. NASA’s Table Mountain facility in the San Bernadino Mountains houses a one-meter laser telescope used as a testbed for refining data tracking in future space missions. That and a variety of space-borne tests have already demonstrated the viability of the concept. One day we may use it for deep space work and who knows, the reach of the laser may someday carry data from a distant star.
For those who want more details on the Alpha Centauri communications paper mentioned above, it’s Lesh et al., “Space Communications Technologies for Interstellar Missions,” Journal of the British Interplanetary Society 49 (1996): 7-14.
by Paul Gilster | Nov 11, 2006 | Astrobiology and SETI |
Since we’ve kicked around the idea of searching for SETI signals in the television bands (as noted in a previous story on Abraham Loeb and the Mileura Wide-Field Array), it’s interesting to note Seth Shostak’s thoughts on the subject. Because although planet Earth has been broadcasting TV signals for some time now, our transmissions are unlikely to be received at any great distance. And that makes a search for accidental TV-like emissions even from relatively nearby stars problematic.
Shostak imagines a civilization 55 light years away hoping to pick up I Love Lucy from Earth. He notes that the non-directional TV signal, assuming a million watts of transmitter power, will reach this distant world “…with a power density of about 0.3 million million million million millionths of a watt per square meter…” And because only a third of the transmission power is in the carrier signal — the most readily detected part of the transmission — even that number is too high.
It’s possible to run these numbers against a new facility, the Low-Frequency Array (LOFAR) now being built in Europe for radio astronomy work. At VHF television frequencies, LOFAR will have an effective collecting area similar to that of the Arecibo dish. Says Shostak:
That’s big. That’s brawny. But not brawny enough. In our SETI experiments at Arecibo, we could find a signal if it were about 0.1 million million million millionths of a watt per square meter. That number, you will notice if you count up the words, is a million times bigger than the “I Love Lucy” carrier at 55 light-years. The aliens’ LOFAR would be inadequate to detect the broadcast by a factor of a million, a not entirely negligible amount. Simply stated: LOFAR couldn’t hear it.
That’s bad news for our hopes of picking up extraneous signals from a technological civilization. It doesn’t disqualify these frequencies from SETI study, but does imply that if we were to find something interesting, it probably wouldn’t be an extraterrestrial sitcom. If any readers have references to other work on the strength of such signals at interstellar distances, please let me know. It’s a question that bears on how visible our own culture is at the distance of nearby stars. The answer may well be that despite I Love Lucy, we’re still all but undetectible.
