Steve Vance

Hydrothermal systems in small ocean planets.

We examine means for driving hydrothermal activity in extraterrestrial oceans on planets and satellites of less than one Earth mass, with implications for sustaining a low level of biological activity over geological timescales. Assuming ocean planets have olivine-dominated lithospheres, a model for cooling-induced thermal cracking shows how variation in planet size and internal thermal energy may drive variation in the dominant type of hydrothermal system-for example, high or low temperature system or chemically driven system. As radiogenic heating diminishes over time, progressive exposure of new rock continues to the current epoch. Where fluid-rock interactions propagate slowly into a deep brittle layer, thermal energy from serpentinization may be the primary cause of hydrothermal activity in small ocean planets. We show that the time-varying hydrostatic head of a tidally forced ice shell may drive hydrothermal fluid flow through the seafloor, which can generate moderate but potentially important heat through viscous interaction with the matrix of porous seafloor rock. Considering all presently known potential ocean planets-Mars, a number of icy satellites, Pluto, and other trans-neptunian objects-and applying Earth-like material properties and cooling rates, we find depths of circulation are more than an order of magnitude greater than in Earth. In Europa and Enceladus, tidal flexing may drive hydrothermal circulation and, in Europa, may generate heat on the same order as present-day radiogenic heat flux at Earths surface. In all objects, progressive serpentinization generates heat on a globally averaged basis at a fraction of a percent of present-day radiogenic heating and hydrogen is produced at rates between 10(9) and 10(10) molecules cm(2) s(1).

Sound velocities and thermodynamic properties of water to 700 MPa and −10 to 100 °C

Sound velocities in liquid water were measured by the method of impulsive stimulated scattering in a sapphire-windowed high-pressure cell from -10 to 100 degrees C and pressures as high as 700 MPa. Velocity measurements are compared with previous experimental efforts relative to the International Association for the Properties of Water and Steam (IAPWS-95) formulation for the equations of state. At 0 and -10 degrees C, sound velocities are in agreement with the one previously published study at sub-zero temperatures to 350 MPa. At ambient and elevated temperatures, differences between the present measurements and IAPWS-95 velocities approach 0.5% near 700 MPa. Inversion of velocity data for density yields results within IAPWS-95 uncertainties, except at the highest temperatures, where elevated sound velocity at high pressure corresponds to as much as -0.2% disagreement with IAPWS-95.

Conference summary: life detection in extraterrestrial samples.

In February 2012, a conference was convened at the Scripps Institution of Oceanography in La Jolla, California, on the subject of life detection in extraterrestrial samples (program and abstracts available at http://www.lpi.usra.edu/meetings/ lifedetection2012). The aim of the conference was to explore the kinds of tools, methods, and approaches necessary for detecting evidence of life in extraterrestrial samples, including those that arrive on Earth by natural processes and those that are deliberately returned by engineered missions. Samples that might be returned from Mars by a future mission were a primary topic of interest. Presentations and discussions at the conference drew upon diverse fields of research, including meteorite studies, modern and ancient terrestrial analog studies, studies of samples returned by past lunar and comet sample return missions, studies of modern traces of life on Earth, and studies of the facilities needed to conduct this kind of research. The conference program was organized with extensive discussion sessions. This report summarizes the results of the conference. The topic of life detection was examined from two different but partially overlapping perspectives: the ‘‘science perspective’’ arising from the desire to know whether life ever arose on Mars and the ‘‘planetary protection perspective’’ arising from the need to protect our own planet from contamination by any potentially harmful living extraterrestrial organisms that may be contained in returned samples. The former relates to detection of any kind of evidence of either ancient or present-day life, whereas the latter is concerned with evidence of present-day viable organisms. A review of the topic of life detection is timely given the scope of recent advances in life-detection studies on Earth, the publication of the National Research Council’s Planetary Science Decadal Survey (which identified seeking the signs of life via Mars sample return (MSR) as its highest priority in the flagship class of missions; National Research Council, 2011), as well as the strategic emphasis within both NASA and ESA on life detection. One of the primary approaches to life detection is via the study of extraterrestrial samples, although other astrobiological approaches also exist. In the case of a potential MSR campaign, significant forward planning is required to ensure best possible practices are implemented throughout the campaign (iMARS Working Group, 2008; MEPAG E2E-iSAG, 2012): from the design and operation of a sample collection rover to containment and preservation of samples in transit, and appropriate handling and analysis of the samples after they have returned to Earth. The array of planned or possible life-detection strategies and measurements has implications for virtually every aspect of a sample return campaign. Thus, it is critical to understand these strategies and measurements well in advance to avoid compromising the fundamental scientific objectives and planetary protection requirements of an MSR campaign. Much of the discussion summarized below assumed MSR would be a robotic endeavor. However, the mission may ultimately involve humans rather than robots. In that case, some aspects of laboratory analyses and sample handling may need to be reassessed. The conference was also an introduction to a subsequent planetary protection workshop dealing specifically with the planetary protection test protocol.

Session 2. Advances in Astrobiological Instrumentation Development

The flux of chemical compounds introduced into the tenuous Europan atmosphere due to energetic charged particle sputtering of the surface ice directly reflects the composition of the ice. In particular, any organic compounds, formed in the sub-ice ocean and entrained in the icy crust, will enter the atmosphere in this sputtering process. This provides the opportunity to remotely determine the surface ice composition through an analysis of the composition of the Europan sputter atmosphere and provides an opportunity to look for astrobiological signatures from Europan orbit. We have developed a preliminary design for an orbiter-based radar spectrometer that can measure minor species in the Europan atmosphere. The radar is sensitive to the total column of molecules between the spacecraft and the surface. Based on conventional radar concepts at longer wavelengths, the instrument concept includes, onboard an orbiter, a transmitter illuminating a spot on the surface and a heterodyne receiver detecting the back-scattered radiation. All molecules in the atmosphere with an electric or magnetic dipole absorb radiation at the millimeter and submillimeter wavelengths at which the spectrometer will operate. Our calculations show that polar species, such as organic Nand S-containing compounds and inorganic salts, if present at ppm levels in the ice, will be detectable. Detection sensitivity is orders of magnitude larger than traditional limb thermal emission spectrometry. In addition, the radar spectrometer observations provide insight into the physical characteristics of the environment (sputter velocities, magnetic field), the surface, and the range between the surface and satellite. 2-02-O. Novel Subcritical Water Extraction Methods for Studying the Mechanisms of Biomarker Preservation in Minerals and Ices