New work out of the Danish National Space Center (DNSC) suggests a startling connection between star-making in the Milky Way and the evolution of life on Earth. During a period of intense star-creation that began some 2.4 billion years ago, ocean-borne bacteria went through cycles of growth and decline of an intensity never since equalled. The Danish study links this variability with incoming cosmic rays that reach Earth from exploded stars. The star-making period in question was a time of numerous supernova explosions. To reach these conclusions, the Space Center's Henrik Svensmark studied the record of heavy carbon in sedimentary rocks. Growing bacteria and algae in ocean waters absorb carbon-12, leaving carbon-13 to enrich the sea; the latter begins to appear in the carbonate shells of sea creatures. By studying variations in carbon-13, Dr. Svensmark can see how much photosynthesis was going on when the shell-making species were alive. And it turns out that the biggest...

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...

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...

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...

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...

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...