Remote sensing of planetary properties and biosignatures on extrasolar terrestrial planets

The major goals of NASA's Terrestrial Planet Finder (TPF) and the European Space Agency's Darwin missions are to detect terrestrial-sized extrasolar planets directly and to seek spectroscopic evidence of habitable conditions and life. Here we recommend wavelength ranges and spectral features for these missions. We assess known spectroscopic molecular band features of Earth, Venus, and Mars in the context of putative extrasolar analogs. The preferred wavelength ranges are 7-25 microns in the mid-IR and 0.5 to approximately 1.1 microns in the visible to near-IR. Detection of O2 or its photolytic product O3 merits highest priority. Liquid H2O is not a bioindicator, but it is considered essential to life. Substantial CO2 indicates an atmosphere and oxidation state typical of a terrestrial planet. Abundant CH4 might require a biological source, yet abundant CH4 also can arise from a crust and upper mantle more reduced than that of Earth. The range of characteristics of extrasolar rocky planets might far exceed that of the Solar System. Planetary size and mass are very important indicators of habitability and can be estimated in the mid-IR and potentially also in the visible to near-IR. Additional spectroscopic features merit study, for example, features created by other biosignature compounds in the atmosphere or on the surface and features due to Rayleigh scattering. In summary, we find that both the mid-IR and the visible to near-IR wavelength ranges offer valuable information regarding biosignatures and planetary properties; therefore both merit serious scientific consideration for TPF and Darwin.     

The NASA Astrobiology Roadmap

The NASA Astrobiology Roadmap provides guidance for research and technology development across the NASA enterprises that encompass the space, Earth, and biological sciences. The ongoing development of astrobiology roadmaps embodies the contributions of diverse scientists and technologists from government, universities, and private institutions. The Roadmap addresses three basic questions: How does life begin and evolve, does life exist elsewhere in the universe, and what is the future of life on Earth and beyond? Seven Science Goals outline the following key domains of investigation: understanding the nature and distribution of habitable environments in the universe, exploring for habitable environments and life in our own solar system, understanding the emergence of life, determining how early life on Earth interacted and evolved with its changing environment, understanding the evolutionary mechanisms and environmental limits of life, determining the principles that will shape life in the future, and recognizing signatures of life on other worlds and on early Earth. For each of these goals, Science Objectives outline more specific high-priority efforts for the next 3-5 years. These 18 objectives are being integrated with NASA strategic planning.     

Vertical mass and moisture structure from TIROS-N

During the First Global GARP Experiment (FGGE), global determinations of mass and moisture were made from TIROS-N (and NOAA-6) infrared and microwave sounding radiance measurements. At NESS in Washington, the meteorological data were produced operationally with a horizontal resolution of 250 km for inclusion in the FGGE level II-b data sets intended for application to large scale numerical analysis and prediction models. High horizontal resolution (50 km) sounding data sets are being produced by NESS and the Space Science and Engineering Center at the University of Wisconsin and at the NASA/Goddard Space Flight Center for special case studies of the “Special Observing Periods” of FGGE.Results are presented to display the characteristics of the sounding data at different resolutions. For the low horizontal resolution data, an evaluation is shown by comparisons of global analyses made only from satellite soundings over land and sea, and those made operationally by the National Meteorological Center, which excluded satellite sounding data over continental areas, but included all conventional data sources. For the high horizontal resolution sounding data, results are presented to demonstrate the delineation of small scale temperature and moisture features which are consistent with the meteorological processes involved.