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.

Tuesday, November 17, 2009

Kevin Zahnle

Co-Investigator, NASA Astrobiology Institute
NASA Ames Research Center

Earth after the Moon-forming Impact

The Earth and Moon were formed by the unequal collision of two planets some 30-100 million years after the Sun was born. The smaller planet is remembered now mostly by its ghost, but the Earth has grown and prospered. This talk addresses the hidden history of the Earth from after the Moon-forming impact until the emergence of a rock record ca 3.8 Ga.

Tuesday, November 24, 2009

No seminar this week.

Tuesday, December 1, 2009

Nancy Kiang, PhD

NASA Goddard Institute for Space Studies
New York, NY

Efficiency of Photon Energy Use for Life Processes: Implications for spectral biosignatures

Chlorophyll a (Chl a) is known as the producer of the two unequivocal signs of life observable at the planetary scale: atmospheric oxygen (in the presence of liquid water) and the reflectance spectrum of plant leaves, in which strong absorbance by Chl a in the red contrasts with scattering in the near-infrared. However, a cyanobacterium, Acaryochloris marina, was recently discovered to utilize chlorophyll d (Chl d) in place of Chl a, to absorb light at much longer wavelengths in the far-red and near-infrared, yet still able to perform oxygenic photosynthesis. A. marina lives in an environment depleted in visible light and enriched in the far-red/near-infrared. This talk presents rationale for measurements currently under way of efficiency of photon energy use in A. marina via pulsed, time-resolved photoacoustic calorimetry (PRTPA). Interpretations of potential results are discussed. This rare variation on oxygenic photosynthesis provides the opportunity to probe the efficiency limits of photon energy use for this process, and whether there is an upper bound on useful photon wavelengths. Answering this question will help constrain the plausible signatures of photosynthesis on extrasolar planets where life is adapted to a different parent star. To what extent are photosynthetic pigment absorbance spectra due to the light environment versus due to molecular mechanisms? What is the minimum energy requirement to produce the essential products for growth? Could extrasolar photosynthesis improve on the efficiency found on Earth, or must it be Earth-like after all?

Tuesday, December 8, 2009

Loren Williams

Professor, Georgia Institute of Technology
School of Chemistry & Biochemistry
Atlanta, GA

Where Did Protein Come From?

Ribosomes are RNA-based macromolecular machines responsible for the synthesis of all proteins in all living organisms. Ribosomes are the most ancient of life's macromolecules and are our most direct link to the deep evolutionary past, beyond the base of the phyologenetic tree. The recent availability high resolution 3D structures of ribosomes provides us with new methods of detection and inference. We will discuss methods for resurrection and biochemical characterization of aboriginal ribosomes.

PAST SEMINARS

Tuesday, October 13, 2009

J. Michael Brown

Professor, Earth and Space Sciences
University of Washington, Seattle

High Pressure Astrobiology: A Tutorial

Life on Earth has been proposed to extend into a "deep biosphere" where as much as half the biomass may reside at pressures approaching 100 MPa. The terrestrial biosphere may be constrained most by the high temperatures found at depth. However, temperatures more favorable to biologic activity are found over an even larger pressure regime (up to 500 MPa) in icy satellites of Jupiter and Saturn. Our research is directed towards exploring the conditions associated with these zones of potential habitability: physical/chemical and the impact of high pressure on biologic systems. The unanswered question remains whether planetary missions can be designed to detect biomarkers for deep life on the icy satellites.

Tuesday, October 20, 2009

View NAI on-line recording of this seminar.

Steve Benner

Distinguished Fellow
The Foundation for Applied Molecular Evolution (Ffame)
Gainesville, Florida

Understanding the Origin of Life

This talk will consider genomics, organic chemistry, and planetary science as we try to understand how the first Darwinian chemical systems arose.

Tuesday, October 27, 2009

View NAI on-line recording of this seminar.

Jade Bond

Research Associate
Lunar and Planetary Laboratory
University of Arizona, Tucson

The Diversity of Extrasolar Terrestrial Planets

The details of the formation of the terrestrial planets are long-standing questions in the geological, planetary and astronomical sciences, with the discovery of extrasolar planetary systems placing even greater emphasis on these questions. To date, very little has been done on combining detailed chemical abundance and distribution models with specific planetary formation simulations. Here we present simulations of the bulk compositions of the terrestrial planets and planetesimals in known extrasolar planetary systems. We find that the terrestrial planets produced vary from resembling the planetary composition of the Solar System to being enriched in Ca and Al, Fe or biogenic species such as O, P and C. These enrichments can be taken to the extreme to produce planets unlike anything previously observed.

Tuesday, November 3, 2009

View NAI on-line recording of this seminar.

Chris McKay

Planetary Scientist
Space Science Division
NASA Ames Research Center

Results from the Mars Phoenix Mission for Mars Habitability and comparisons to Mars-like places on Earth

Phoenix investigated soil and ice in the martian polar regions. The results of this mission and a comparison with Mars-like sites on Earth provide a basis for considering the limits of life and the possibility of life on Mars in the recent or distant past. Mars-like sites on Earth include arid deserts and the polar regions. Studies of the dry permafrost in Antarctica suggests that the Phoenix site may have been habitable as recently as 5 Myr ago.