Quantifying the Origins of Life on a Planetary Scale

A simple, heuristic formula with parallels to the Drake Equation is introduced to help focus discussion on open questions for the origins of life in a planetary context. This approach indicates a number of areas where quantitative progress can be made on parameter estimation for determining origins of life probabilities. We also suggest that the probability of origin of life events can be dramatically increased on planets with parallel chemistries that can undergo the development of complexity, and in solar systems where more than one planet is available for chemical evolution, and where efficient impact ejecta exchange occurs, increasing the effective chemical search space and available time.Comment: 13 pages, submitted to Scienc

Exoplanet Transit Parallax

The timing and duration of exoplanet transits has a dependency on observer position due to parallax. In the case of an Earth-bound observer with a 2 AU baseline the dependency is typically small and slightly beyond the limits of current timing precision capabilities. However, it can become an important systematic effect in high-precision repeated transit measurements for long period systems due to its relationship to secular perspective acceleration phenomena. In this short paper we evaluate the magnitude and characteristics of transit parallax in the case of exoplanets using simplified geometric examples. We also discuss further implications of the effect, including its possible exploitation to provide immediate confirmation of planetary transits and/or unique constraints on orbital parameters and orientations.Comment: 12 Pages, 3 Figures, Accepted for publication in Ap

Optimal Chandra/XMM-Newton Band-Passes for Detecting Low Temperature Groups and Clusters of Galaxies

In this short paper I present the results of a calculation which seeks the maximum, or optimal, signal-to-noise energy band for galaxy group or cluster X-ray emission detected by the Chandra and XMM-Newton observatories. Using a background spectrum derived from observations and a grid of models I show that the "classical" 0.5-2 keV band is indeed close to optimal for clusters with gas temperatures >2 keV, and redshifts z<1. For cooler systems however, this band is generally far from optimal. Sub-keV plasmas can suffer 20-60% signal-to-noise loss compared to an optimal band, and worse for z>0. The implication is that current and forthcoming surveys should be carefully constructed in order to minimize bias against the low mass, low temperature end of the cluster/group population.Comment: 9 pages, 4 postscript figures, uses AASTEX, accepted Ap

Rebuilding the Habitable Zone from the Bottom Up with Computational Zones

Computation, if treated as a set of physical processes that act on information represented by states of matter, encompasses biological systems, digital systems, and other constructs, and may be a fundamental measure of living systems. The opportunity for biological computation, represented in the propagation and selection-driven evolution of information-carrying organic molecular structures, has been partially characterized in terms of planetary habitable zones based on primary conditions such as temperature and the presence of liquid water. A generalization of this concept to computational zones is proposed, with constraints set by three principal characteristics: capacity, energy, and instantiation (or substrate). Computational zones naturally combine traditional habitability factors, including those associated with biological function that incorporate the chemical milieu, constraints on nutrients and free energy, as well as element availability. Two example applications are presented by examining the fundamental thermodynamic work efficiency and Landauer limit of photon-driven biological computation on planetary surfaces and of generalized computation in stellar energy capture structures (a.k.a. Dyson structures). It is shown that computational zones involving nested structures or substellar objects could manifest unique observational signatures as cool far-infrared emitters. While this is an entirely hypothetical example, its simplicity offers a useful, complementary introduction to computational zones.Comment: 31 pages, 3 figures, submitted to The Astrobiology Journa

X-Ray Detection of an Obscured Active Galactic Nucleus in a z=3.09 Radio-quiet Ly-alpha Nebula

We present evidence for a highly obscured X-ray source in one of two giant Ly-alpha emission nebulae in the z=3.09 proto-cluster region SSA22. Neither Ly-alpha nebula is associated with significant radio emission. While one has a significant submillimeter detection and is undetected in the X-ray, the other is a factor of 2-10 times less submillimeter bright and appears to contain a hard-band X-ray source. We discuss our analysis and techniques for assessing the X-ray properties of this source and suggest that we have detected an embedded AGN source in one of these nebulae which may be at least partially responsible for exciting the Ly-alpha emission through a mechanism that is essentially decoupled from the radio, submillimeter, or optical luminosities. We also present an upper limit on the mean X-ray emission from 10 other extended Ly-alpha objects in the SSA22 region.Comment: 12 pages, 3 figures, accepted to appear in ApJL, Vol. 615, 2004 November 1