NAI Newsletter

11/30 NAI Director's Seminar: Andrew Pohorille, "Is Water Necessary for Life?"

Date/Time: Monday, November 30, 2009 11:00AM Pacific Speaker: Andrew Pohorille (NASA Ames Research Center) Abstract: “Follow the water” is the canonical strategy in searching for life in the universe. Conventionally, discussion of this topic is focused on the ability of a solvent to support organic chemistry sufficiently rich to seed life. Although this is a necessary condition for the emergence of life it is far from being sufficient. Perhaps more importantly, solvent must promote self-organization of organic matter into functional structures capable of responding to environmental changes. In biology, they are mostly based on non-covalent interactions (interactions that do not involve making or breaking chemical bonds), strength of which must be properly tuned. If non-covalent interactions were too weak, the system would exhibit undesired, uncontrolled response to natural fluctuations of physical and chemical parameters. If they were too strong kinetics of biological processes would be slow and energetics costly. Non-covalent interactions are very strongly mediated by the solvent. In particular, potential solvents for life must be characterized by a high dielectric constant to ensure solubility of polar species and sufficient flexibility of biological structures stabilized by electrostatic interactions. Among these solvents, water exhibits a remarkable trait that it also promotes solvophobic (hydrophobic) interactions between non-polar species, typically manifested by a tendency of these species to aggregate and minimize their contacts with the aqueous solvent. Hydrophobic interactions are responsible, at least in part, for many self-organization phenomena in biological systems, such as the formation of cellular boundary structures or protein folding. Strengths of electrostatic and hydrophobic interactions are similar and can be balanced over a wide range of temperatures, which considerably increases the repertoire of interactions that can be used to modulate biological functions. Some properties of water, e.g. its chemical activity against polymerization reactions, are considered as unfavorable to life. In actuality, this might be a favorable trait because life requires a balance between constructive and destructive processes. For example, molecules synthesized in response to specific conditions must be degraded once these conditions change. Otherwise regulation of biological processes would be virtually impossible. Water might not be the only liquid with favorable properties for supporting life. One example is formamide, which might be present elsewhere in the universe in sufficient quantities to warrant interest as a potential alternative to water for the origin of life. However, further studies on physical, chemical and biological properties of non-aqueous solutions are needed to draw firmer conclusions on this subject. For more information and participation instructions: http://astrobiology.nasa.gov/nai/seminars/detail/161

UH Team Member Tobias Owen Receives 2009 Gerard P. Kuiper Prize in Planetary Sciences

The NAI extends its congratulations to University of Hawaii team member Tobias Owen for receiving the 2009 Gerard P. Kuiper Prize. The Gerard P. Kuiper Prize was established by the Division for Planetary Sciences (DPS) to recognize and honor outstanding contributors to planetary science. It is to be awarded to scientists whose achievements have most advanced our understanding of the planetary system. For more information: http://dps.aas.org/prizes/kuiper

11/10 University of Washington Astrobiology Seminar: Kevin Hand, "Joule Heating of the South Polar Terrain on Enceladus"

Date/Time: Tuesday November 10, 2009 2:30PM Pacific Speaker: Kevin Hand (Jet Propulsion Laboratory) Abstract: The plumes and observed heat flux in the South Polar Terrain of Enceladus remain a considerable mystery. We report that Joule heating in Enceladus – resulting from the interaction of Enceladus with Saturn's magnetic field – may account for several, to a few tens of megawatts of power across the observed "tiger stripe" fractures. Electric currents passing through subsurface channels of low salinity and just a few kilometres in depth could supply a source of power to the South Polar Terrain, providing a small but previously unaccounted for contribution to the observed heat flux and plume activity. For more information and participation instructions: http://astrobiology.nasa.gov/nai/seminars/detail/164

Oxygen Production in Earth's Early Oceans Predates the Great Oxidation Event

It is widely accepted that around 2.4 billion years ago, the Earth’s atmosphere underwent a dramatic change when oxygen levels rose sharply. Called the “Great Oxidation Event” (GOE), the oxygen spike marks an important milestone in Earth’s history, the transformation from an oxygen-poor atmosphere to an oxygen-rich one paving the way for complex life to develop on the planet. Two questions that remain unresolved in studies of the early Earth are when oxygen production via photosynthesis got started and when it began to alter the chemistry of Earth’s ocean and atmosphere. A research team that includes members of NAI’s Arizona State University team corroborates recent evidence that oxygen production began in Earth’s oceans at least 100 million years before the GOE, and goes a step further in demonstrating that even very low concentrations of oxygen can have profound effects on ocean chemistry. Their study is published in the current issue of Science. To arrive at their results, the researchers analyzed 2.5 billion-year-old black shales from Western Australia, samples provided through the NAI’s Astrobiology Drilling Program. Essentially representing fossilized pieces of the ancient seafloor, the fine layers within the rocks allowed the researchers to page through ocean chemistry’s evolving history. Specifically, the shales revealed that episodes of hydrogen sulfide accumulation in the oxygen-free deep ocean occurred nearly 100 million years before the GOE and up to 700 million years earlier than such conditions were predicted by past models for the early ocean. Scientists have long believed that the early ocean, for more than half of Earth’s 4.6 billion-year history, was characterized instead by high amounts of dissolved iron under conditions of essentially no oxygen. Said Timothy Lyons of UC Riverside who led the study, “This is important because oxygen-poor and sulfidic conditions almost certainly impacted the availability of nutrients essential to life, such as nitrogen and trace metals. The evolution of the ocean and atmosphere were in a cause-and-effect balance with the evolution of life.”

'Ultra-Primitive' Particles Found in Comet Dust

Dust samples collected by high-flying aircraft in the upper atmosphere have yielded an unexpectedly rich trove of relicts from the ancient cosmos, report scientists from NAI’s Carnegie Institution of Washington team in Earth and Planetary Science Letters. The stratospheric dust includes minute grains that likely formed inside stars that lived and died long before the birth of our sun, as well as material from molecular clouds in interstellar space. This “ultra-primitive” material likely wafted into the atmosphere after the Earth passed through the trail of an Earth-crossing comet in 2003, giving scientists a rare opportunity to study cometary dust in the laboratory. At high altitudes, most dust in the atmosphere comes from space, rather than the Earth’s surface. Thousands of tons of interplanetary dust particles (IDPs) enter the atmosphere each year. “We’ve known that many IDPs come from comets, but we’ve never been able to definitively tie a single IDP to a particular comet,” says study coauthor Larry Nittler, of Carnegie’s Department of Terrestrial Magnetism. “The only known cometary samples we’ve studied in the laboratory are those that were returned from comet 81P/Wild 2 by the Stardust mission.” NASA’s Stardust mission collected samples of comet dust, returning to Earth in 2006. Comets are thought to be repositories of primitive, unaltered matter left over from the formation of the solar system. Material held for eons in cometary ice has largely escaped the heating and chemical processing that has affected other bodies, such as the planets. However, the Wild 2 dust returned by the Stardust mission included more altered material than expected, indicating that not all cometary material is highly primitive. The IDPs used in the current study were collected by NASA aircraft in April 2003, after the Earth passed through the dust trail of comet Grigg-Skjellerup. The research team, which included Carnegie scientists Nittler, Henner Busemann (now at the University of Manchester, U.K.), Ann Nguyen, George Cody, and seven other colleagues, analyzed a sub-sample of the dust to determine the chemical, isotopic and microstructural composition of its grains. “What we found is that they are very different from typical IDPs” says Nittler. “They are more primitive, with higher abundances of material whose origin predates the formation of the solar system.” The distinctiveness of the particles, plus the timing of their collection after the Earth’s passing through the comet trail, point to their source being the Grigg-Skjellerup comet. “This is exciting because it allows us to compare on a microscopic scale in the laboratory dust particles from different comets,” says Nittler. “We can use them as tracers for different processes that occurred in the solar system four-and-a-half billion years ago.” The biggest surprise for the researchers was the abundance of so-called presolar grains in the dust sample. Presolar grains are tiny dust particles that formed in previous generations of stars and in supernova explosions before the formation of the solar system. Afterwards, they were trapped in our solar system as it was forming and are found today in meteorites and in IDPs. Presolar grains are identified by having extremely unusual isotopic compositions compared to anything else in the solar system. But presolar grains are generally extremely rare, with abundances of just a few parts per million in even the most primitive meteorites, and a few hundred parts per million in IDPs. “In the IDPs associated with comet Grigg-Skjellerup they are up to the percent level,” says Nittler. “This is tens of times higher abundances than we see in other primitive materials.” Also surprising is the comparison with the samples from Wild 2 collected by the Stardust mission. “Our samples seem to be much more primitive, much less processed, than the samples from Wild 2,” says Nittler, “which might indicate that there is a huge diversity in the degree of processing of materials in different comets.”

Ribosomes as Ancient Molecular Fossils

Members of NAI’s team at Georgia Tech have a new paper in Molecular Biology and Evolution describing an analysis of ribosomal structure and sequence. Their approach chronicles the ribosome’s evolution, effectively interpreting the ribosome as a fossil. Using the highest resolution structures available, of two species that represent disparate regions of the evolutionary tree, they have sectioned the large subunit of each ribosome into concentric shells, like an onion, using the site of peptidyl transfer as the origin. Their results suggest that the structure and interactions of both RNA and protein can be described as changing, in an observable manner, over evolutionary time.