Centauri Dreams

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.

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.

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.

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.

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.

Shrinking our instrumentation is one of the great hopes for extending spacecraft missions into the Kuiper Belt and beyond. No matter what kind of propulsion system we’re talking about, lower payload weight gets us more bang for the buck. That’s why a new imaging system out of Rochester Institute of Technology catches my eye this morning. It will capture images better than anything we can fly today, working at wavelengths from ultraviolet to mid-infrared.

It also uses a good deal less power, but here’s the real kicker: The new system shrinks the required hardware on a planetary mission from the size of a crate down to a chip no bigger than your thumb. The creation of Zeljko Ignjatovic and team (University of Rochester), the detector uses an analog-to-digital converter at each pixel. “Previous attempts to do this on-pixel conversion have required far too many transistors, leaving too little area to collect light,” said Ignjatovic. “First tests on the chip show that it uses 50 times less power than the industry’s current best, which is especially helpful on deep-space missions where energy is precious.”

Precious indeed. But imagine the benefits of carrying miniaturization still further. Nanotechnology pioneer Robert Freitas has speculated provocatively about space probes shrunk from the bulk of a Galileo or Cassini into a housing no larger than a sewing needle. Launched by the thousands to nearby stars, such probes could turn their enclosed nano-scale assemblers loose on the soil of asteroids or moons in the destination system. They could build a macro-scale research station, working from the molecular level up to create tools for continuing investigation and communicating data back to Earth.

The new sensor out of Rochester is a long way from that kind of miniaturization, but surely the dramatic changes in computing over the past few decades have shown us how potent shrinking our tools — and packing more and more capability into them — can be. And when you’re working with finite payload weight and can insert a new set of tools because they’re smaller than before, you’ve dramatically extended what a given space mission can accomplish. Getting a millimeter-wide needle to Alpha Centauri may not be Star Trek, but it could be how we start.

Hunting for terrestrial planets is not going to be easy, and even when we start getting images of such worlds, there will be plenty of questions to answer. How to detect life on a terrestrial planet was one of the subjects that came up in September at the Pale Blue Dot workshop at Adler Planetarium in Chicago. Cassini’s recent picture of Earth from Saturn space, much like Voyager’s ‘pale blue dot’ image of 1990, reminded everyone at the conference of our fragile place in the cosmos. It also forced the question of how we might find other such worlds.

And finding a blue planet in a star’s habitable zone isn’t enough. As laid out in this JPL backgrounder, the key will be to gather enough spectral data to make a judgment call that could change how we view our place in the universe. Breaking down the light from a distant planet should tell us much about its chemical composition. Carbon dioxide and water vapor, for example, are both clues to life, their dual presence suggesting both an atmosphere and an ocean.

But even liquid water isn’t sufficient to make the call. In reality, we’ll need a combination of things. Oxygen is useful because it suggests plant life or some kind of living cycle to produce it and keep it in the atmosphere. Methane likewise suggests life processes at work, though by itself it’s not sufficient (we can certainly find the stuff in places where life seems less likely, as witness Titan). So here’s the take from the JPL story:

Scientists say that oxygen is a more reliable sign of life than methane, but if they found large quantities of both, they’d be more convinced. “Finding two of these molecules together would be much better than one. The more, the better,” said Dr. Victoria Meadows of NASA’s Spitzer Science Center, Pasadena, who served as chair of the third Pale Blue Dot conference. “For example, if we found carbon dioxide, oxygen and water vapor, in addition to methane, then we’d be pretty convinced that we were looking at an environment like our own.”

Centauri Dreams’ take: Inevitably, the hunt for extraterrestrial life looks first for the kind of life we find on Earth. But we may have to widen that view, and the key is to make as few assumptions as possible. For if we’ve learned one thing from the 200+ extrasolar planets found thus far, it’s that solar systems around other stars can be utterly different from anything we had imagined. Finding that alien blue dot with the right mix of chemicals in its atmosphere would be profoundly suggestive, but it doesn’t rule out more bizarre abodes of life that we don’t yet know how to categorize. Not all those pale, living dots are going to be blue.

Though I hadn’t planned another entry for today, this is just too beautiful to pass up. We’re looking at the Orion nebula (be sure to click the image to enlarge) in infrared, ultraviolet and visible light, a composite using both Hubble and Spitzer data that brings out unheard of detail — the green swirls are from Hubble’s ultraviolet and visible light detectors; the red and orange are Spitzer working in the infrared. This massive star formation region located in the sword of Orion is home to about 1000 young stars.

Note the set of stars called the Trapezium, identifiable as a bright area near the center of the image. Each of these massive stars pours out ultraviolet that heats hydrogen and sulphur in the nebula. The stellar wind from clusters of stars embedded in the dust and gas helped to create the distinctive shapes and swirls of this celestial artwork.

Titan’s atmosphere may be telling us something about conditions on the early Earth. It’s thick and filled with interesting things like organic aerosol particles that form through the reaction of sunlight with methane gas. Translate that into terrestrial terms and you get a similarly hazy early Earth whose surface receives more than 100 million tons of organic materials every year. “As these particles settled out of the skies, they would have provided a global source of food for living organisms,” said Melissa Trainer (University of Colorado - Boulder).

Trainer is principal author of a new paper that examines the chemical qualities of these aerosol particles in the laboratory, studying their chemical composition, size and shape. The method: expose a mixture of methane and nitrogen to ultraviolet light, then add carbon dioxide to see if organic haze forms. And indeed, the haze forms readily in a wide range of methane and carbon dioxide concentrations. That smoggy sky over Titan may be similar to the haze that hung over the Earth for millions of years as the conditions for life emerged.

Image: As Cassini approached Titan on Aug. 21, 2005, it captured this natural color view of the moon’s orange, global smog. Images taken with the wide-angle camera using red, green and blue spectral filters were combined to create this color view. Credit: NASA/JPL/Space Science Institute.

Another benefit of the haze layer would be protection, shielding primitive organisms from ultraviolet light from the Sun and helping to stabilize the early climate. “It’s somewhat similar to the smog in Los Angeles,” adds Trainer. “Today’s haze on Earth is also created photochemically, which means sunlight powers chemical reactions in the atmosphere. However, the early atmosphere of Earth had different gases present, so chemical composition of the early haze is very different than the haze we have today. There also would have been a lot more of it.”

The paper is Trainer et al., “Organic Haze on Titan and the Early Earth,” accepted for publication in Proceedings of the National Academy of Sciences. The study was performed for NASA’s Astrobiology Institute.

Imagine our Sun spewing out a flare 100 million times stronger than usual, releasing the energy of 50 million trillion atomic bombs. The effect on our planet would be catastrophic. Fortunately, what the Swift satellite has spotted occurred a bit further away in a binary system called II Pegasi, some 135 light years from Earth. Swift is designed to detect gamma-ray bursts — the most powerful of all explosions — and this flare was energetic enough to produce a false alarm for such a burst.

NOTE: The original entry here referenced the power of ‘fifty trillion’ atomic bombs; the actual figure used by NASA was corrected, as above, to ‘fifty million trillion.’ Thanks to Robin Goodfellow for catching the typo.

II Pegasi is an interesting system. The flare star is 0.8 times the mass of the Sun; its companion is 0.4 solar masses, and the stars are separated by only a few stellar radii. That produces fast rotation on both stars, and while II Pegasi may be a billion years older than the Sun, the tight orbit has something to do with the flare activity. “The tight binary orbit in II Pegasi acts as a fountain of youth, enabling older stars to spin and flare as strongly as young stars,” said Steve Drake of NASA Goddard, a co-author with Rachel Osten of an upcoming Astrophysical Journal paper.

The cosmos is both a life-giving and a life-taking place. Some believe that stellar outbursts like this one may be a factor in conditioning interstellar dust that will later form into planets, immense violence that eventually produces life. But such a flare could be a civilization-ender if it occurred on a star like ours. The x-ray outpouring would produce climate change and, doubtless, mass extinction. X-ray emissions from II Pegasi lasted for several hours; a normal solar flare produces emissions that may last a few minutes.

Image: A typical solar flare from our sun, from September 2005, captured in the X-ray waveband by NASA’s TRACE satellite. Note the bright magnetic loops of matter. The twisting and reconnecting of these loops initiate the flare. NASA’s Swift satellite detected a similar flare from a star system called II Pegasi 135 light-years from Earth… except it was one hundred million times more energetic than the sun’s typical solar flare. Had it been from our sun, it would have triggered a mass extinction on Earth. The II Pegasi flare was too distant (fortunately) to image in detail. Credit: NASA/LMSAL.

Flares aren’t on the agenda, but extinction events of a more localized sort will be discussed at the 2007 Planetary Defense Conference, to be held next March 5-8 at George Washington University in Washington, DC. The objective of the conference is to create a white paper that analyzes the current state of the art in detection and tracking of near Earth objects (NEOs), and the methods we might use to defend ourselves against them. Registration opens in December; let’s hope the conference gets plenty of press coverage.

And finally, a 48-minute documentary with the same name — “Planetary Defense” — is now being produced to depict the various efforts at detection and deflection of asteroids and comets with Earth-crossing orbits. Numerous experts in the field are said to be involved, along with science fiction legend Arthur C. Clarke, who began his 1973 novel Rendezvous with Rama with a major asteroid impact (on a September 11, no less, though one set 75 years in the book’s future). Project Spaceguard is the result, a determined response to incoming objects that, we must hope, will one day become reality in the form of a robust space-based infrastructure throughout our Solar System.