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2004 Annual Science Report

University of California, Los Angeles Reporting  |  JUL 2003 – JUN 2004

Executive Summary

The UCLA astrobiology research program progressed on four fronts in the past nine months. These four fronts, or themes, are: 1) extrasolar planetary systems and the origins of organic molecules; 2) habitability of planets and their satellites; 3) Earth’s early environment and life; and 4) evolution of biological complexity. Research completed as part of our first year of participation in the NASA Astrobiology Institute’s third Cooperative Agreement has provided some answers pertaining to key questions in astrobiology, including: Is there evidence for life-sustaining water associated with rocky bodies in extrasolar planetary systems? Are terrestrial planets likely to be stable in the wide variety of planetary configurations observed around other stars? What controls the potential habitability of Jupiter’s Galilean moons? What was the source of the bolide that collided with Earth in the late Eocene? When did life first appear on Earth? How can transition metal isotopes be used as tracers of biological processes? Can the biogenicity of ancient microfossils be established conclusively or not? How important was horizontal gene transfer for facilitating the evolution of early life on Earth? The many projects reported on in this annual report can be grouped according to the four themes described above. Some of the results of these studies are summarized below.

Extrasolar planetary systems: Several advances in our understanding of extrasolar planetary systems were made this past year. UCLA astronomers have placed limits on the mass of icy and rocky bodies resembling our own Kuiper belt objects (KBOs) that might exist around other stars. On a similar line of inquiry, UCLA astronomers have proposed a new method for detecting oceans on planets around other stars. The method relies on the fact that so-called main-sequence stars like our own become more luminous with time. This increase in luminosity can lead to evaporation of oceans on orbiting planets resembling Earth. The gaseous water released by this evaporation would leave a spectroscopic signal detectable as the water passes in front of the star. Our astronomers have also made progress in trying to understand the conditions that lead to the formation of the only known examples of extrasolar planets with masses comparable to Earth. The problem is intriguing because these Earth-mass planets orbit around a pulsar (PSR1257+12). The space around pulsars would not be the first places to search for planets as they are the remains of a giant explosion that destroyed a massive star. It appears that in this case the explosion may have also destroyed a companion star the remains of which were left to form a protoplanetary disk around the remaining core. Understanding the ways that planets form in these rather bizarre circumstances would help us to understand whether or not we should be counting circumpulsar environs as potential sites for planets harboring life. Another potential environment for terrestrial-like planet formation might be within so-called second generation planetary systems formed after the merger of two stars. Our team has been granted observing time on the Spitzer Space Telescope to search for evidence for such oddball planetary systems.

Theoretical studies of the stability of a small Earth-like planet in the presence of a giant planet like those known to orbit other stars have been carried out this year. Results provide a “map” of orbital configurations that are stable with respect to the smaller planet.

The origin of organics: UCLA team members ordered parts for the UCLA First Light Infrared Test Experiment Camera (FLITECAM) instrument to carry out astrobiological research on the Stratospheric Observatory for Infrared Astronomy (SOFIA) (Figure 1). The fruits of this work should occur in 2006 and will allow detection in space of dust composed of organic compounds.

Habitability of planets and their satellites: Our team has moved forward with studies of the features of the icy moons of Jupiter that make these solar system bodies potential homes for primitive life. Focus has been placed on heat transport in the Galilean moons as this will control the state of water on these relatively wet bodies. Our most recent work on Europa’s icy shell shows that tidal dissipation can cause melting of water ice only near the base of the ice layer, meaning that tides imparted by Jupiter are not the cause of some of the physiographic features that result from periodic melting of water ice seen on the surface of Europa.

A key feature of habitability is the presence of volatiles on a planet. Our team published this year results of a study showing that volatiles, comprising the atmospheres and even oceans, can be added to a planet by large impacts of volatile-bearing asteroids or comets. The study shows that retention of volatiles carried by the impacting body depends on the planet’s gravity (escape velocity) and the speed and trajectory of the impactor. The investigators conclude that, contrary to the conclusions of some earlier studies, Earth could well have acquired its inventory of volatiles by such impacts.

Climate change on Mars is controlled by the tilt of the planet’s axis of rotation, referred to as obliquity. UCLA scientists developed a computer model of the Martian obliquity history. Results obtained this past year indicate that deformation of the planet may play a key role in determining obliquity and therefore climactic change.

Earth’s early environment and life: A key to understanding the history of life on Earth is developing reliable methods for identifying fossil microbes. Our team has begun construction of a new Raman imaging facility that will be used to help to resolve outstanding questions regarding the biogenicity of very old putative fossil microbes.

The partitioning of the stable isotopes of light elements can be used in a variety of ways to investigate links between the biosphere and lithosphere. In some cases isotope partitioning might be useful as a clue to the presence of biological activity (a biomarker). In other cases an isotopic signal can be used as a proxy for climate change that can be correlated with evolutionary changes. During this past year several new laboratories at UCLA have contributed to improved understanding of the variability of isotope ratios with application to the astrobiological sciences. Our team has shown for the first time that the process of transferring an electron can lead to partitioning of transition metal isotopes in ways that resemble the effects seen in biological systems. These findings raise the possibility that it is the electron transfer itself that results in a selectivity of one isotope over another when organisms utilize transition metals. Identification of the mechanism of biological isotope selectivity enhances the prospects for using such signals as biomarkers. In another study, we have completed in these past few months thousands of carbon and oxygen isotope analyses of a complete section of Cambrian limestone from Siberia that marks a pronounced excursion in Earth’s carbon isotopic record closely related to a mass extinction event. This new isotopic record can be correlated with biostratigraphic zones to help resolve questions surrounding the causes of these enigmatic isotopic features in Earth history that appear to be associated with changes in biological diversity.

The “great oxidation event” during which free oxygen became plentiful in Earth’s atmosphere is marked by a drastic reduction in the presence of mass independent fractionation (MIF) effects among the isotopes of sulfur. Our team has been examining the cause of the MIF effects in sulfur to better understand their links with the presence or absence of O2 in a planetary atmosphere. Toward this end, SO2 photodissociation experiments were performed this year demonstrating that the effects of broadband ultraviolet light are different from those effects obtained for narrow bands. These findings are particularly relevant since photolysis in atmospheres will result from broadband rather than narrowband exposure.

Impacts of comets and/or asteroids almost certainly play a fundamental role in the origin, evolution, and extinction of life. The influence of impacts on evolving life on Earth was most acute in the early history of our planet. Against this backdrop, members of the UCLA team carried out geochemical studies of sediments from several known impact and extinction horizons ranging in age from late Pliocene (2.4 million year old) through early Archean (3.5 billion years old). The sediments examined include those representing the greatest mass extinction events in Earth history. Among the most recent findings are that a late Eocene impactor came from the Main Asteroid belt, suggesting that an episode of numerous asteroid collisions in the asteroid belt ultimately lead to the Eocene impacts. The implications are clear; events in the asteroid belt may have had profound influence on the history of life on our planet.

Rocks from Akilia Island , Greenland , have been reported to contain evidence for extraordinarily ancient life on Earth (> 3.8 billion years old). The age and origin of these rocks have been the subject of much debate, however. Studies just completed by UCLA team members support a >3.8 billion year old age and a chemical sedimentary origin for the controversial Fe-rich quartz-pyroxene rocks that contain the evidence for life. As an outgrowth of this controversy, our team members engaged in Akilia geology led an NAI-sponsored field trip to examine evidence for >3.8 Ga life on Earth. Seventeen field-trip participants traveled to west Greenland in June 2004 to visit key early life localities (Figure 2) and discuss their origin in the field and in sessions held in the capitol city of Nuuk .

Evolution of biological complexity: Genomics is providing a new window on the ways in which life evolves to greater levels of complexity. Members of the UCLA team made progress this year on the ways that horizontal gene transfer, by which organisms living in similar environments preferentially exchange genes, affected the progress of evolution on Earth. Their findings published this year indicate that prokaryotic genome innovation was accelerated by horizontal gene transfer by a factor of 10,000. These same workers reported this year their development of a new phylogenetic analysis tool that uses the presence or absence of genes to determine phylogenetic trees. The new method of conditioned reconstruction mitigates the polluting effects of horizontal gene transfer. In a separate genomic study, our team explored the origins of the process of microbial sulfate reduction and its potential as an important process on early Earth. Results show that sulfate reduction may be far more common among Archaea than previously assumed, making it more likely that microbial sulfate reduction was an important component of ancient Earth’s geochemical cycles.

UCLA-sponsored astrobiologists have progressed on several fronts pertaining to ancient animal life this year. Microbial studies on early Cambrian fossils confirm that shifts in body symmetry occurred several times in animal evolution. Sense organs are a fundamental feature of animal life. Studies of the evolution of the developmental genetics of sensory and neural systems in basal animals continued this year. Our group reported work on the eye/sense organ developmental gene sine oculis from sponges, jellyfish, ctenophores and basal bilaterians, including flatworms and mollusks. The work demonstrates the presence and, in the case of jellyfish, expression of these sense organ related genes, providing critical insight into the evolution of sense organs. We continue to make progress in this area with recovery of other sense organ genes such as optix and eyes absent in basal animals. We have also been successful in the first stages of recovery of genes that we infer to be important in the evolution of the skeletons of Bilateria. This investigation of the developmental underpinnings of invertebrate skeletogenesis will ultimately allow us to integrate the fossil record of evolution.

Figure 1

Figure 1: A nearly-monochromated image of the planetary nebula NGC 7027. The image shows bright emission at a wavelength of 3.3 microns from polycyclic aromatic hydrocarbons (PAHs). The infrared picture was obtained using FLITECAM, the first-light near-infrared test camera for NASA’s SOFIA , during ground-based trials at the University of California 's Lick Observatory. The instrument also has a new spectroscopic mode that allows the emission feature to be resolved. When SOFIA operations begin, the UCLA team will use FLITECAM to study the development and evolution of these carbon chain molecules in stellar environments.

Figure 2

Figure 2: Rocks showing possible evidence for early life on Earth 3.8
billion years ago, Akilia Island, west Greenland. The locality was
visited during an NAI-sponsored field trip in June, 2004, led by UCLA
team member Craig Manning.