Charting Course: Life in the Universe
The National Academy of Science released this summer their pre-publication report (PDF) on astrobiology, entitled "Life in the Universe". The Space Studies Board highlighted the major findings so far. Excerpts show the exciting directions for next milestones.
|Our Milky Way galaxy is packed with 400 billion stars and perhaps even more planets. "We are not looking for a grand vision. We are looking for the beginnings of vision." -John Baross, 2001, University of Washington, Co-chair. Committee on the Evolution and Origins of Life|
The past few years have witnessed the discovery of planets around other stars, strong circumstantial evidence for a liquid water ocean beneath the surface of Jupiter’s moons Europa, Ganymede, and Callisto, controversial claims for biological activity in a martian meteorite, the discovery of life in extreme terrestrial environments, and a genuine revolution in our understanding and manipulation of the genetic mechanisms of the living cell.
Significant scientific advances have occurred in the past 5 years in addressing some of the questions identified in the astrobiology roadmap. A few example areas that have borne particular fruit, with example references include the following:
- Analysis of complex organic chemistry in interstellar clouds of gas and dust that give rise to new stars and solar systems;
- Direct study of extrasolar giant planets through transits and spectra;
- Discovery that living organisms, normally found on Earth’s surface, can survive at extreme pressure;
- Evidence from geologic features that liquid water once flowed on the surface of the planet Mars;
- Indications from magnetic field geometry that liquid water likely exists today below the icy crust of Jupiter’s moon Europa;
- Ground-based studies of Titan indicating both temporal and spatial variability, and the presence of organic molecules;
- Chemical-isotopic hints that microbial life on Earth existed 3.9 billion years ago, almost to the period of early heavy cometary bombardment;
- Evidence that liquid water existed in the crust of the Earth some 4.3 billion years ago;
- Elucidation of the detailed history of evolution and the phylogenetic relationships among organisms; and
- In vitro evolution experiments that have come close to developing self-replicating systems in the laboratory.
The mix of flight programs, which run from Discovery missions (e.g., Mars Pathfinder, Near-Earth Asteroid Rendezvous, and Stardust) through to flagship mission (e.g., Galileo and Cassini), provides a varied tapestry of flight-preparation times, risks, and rewards.
Notable among these has been the spectacular exploration of the outer solar system, commencing with the Pioneer missions, through the Voyager discoveries about the satellite systems of the giant planets, and culminating in the Galileo discoveries about Europa and the promise of Cassini discoveries at Saturn.
Laboratory studies have blossomed as well, because techniques developed to analyze the Apollo lunar samples have been applied to the large numbers of meteorite samples found, serendipitously, through Antarctic exploration. Among these samples are pieces of Mars and the Moon, and laboratory studies inspired the goal of directly collecting small body samples that is being realized through the ongoing Stardust mission.
Perhaps most extraordinarily, the detection and now characterization of extrasolar planets has created a new intellectual realm within planetary science, and as well has produced profound synergies between observational planetary astronomy and its parental roots in large telescopic observations of the cosmos. Giant planets are being detected indirectly and, in a few cases, observed directly to allow analyses of their bulk and atmospheric properties. Flight opportunities range in scale from Explorer (microlensing) through Discovery (Kepler-transits) to flagship (Space Interferometry Mission) missions.
One cannot come away from the national astrobiology meetings without remarking how well the big questions are being addressed, how easy it is to explain to the informed layman what the research means, and the extent to which talented students are attracted to this research area.
 P. Ehrenfreund, M.P. Bernstein, J.P. Dworkin, S.A. Sandford, and L.J. Allamandola, "The Photostability of Amino Acids in Space," Astrophysical Journal Letters 550: 95-99, 2001.
 D. Charbonneau, T.M. Brown, R.W. Noyes, and R.L. Gilliland, "Detection of An Extrasolar Planet Atmosphere," Astrophysical Journal 568: 377-384, 2002.
 A. Sharma, J.H. Scott, G.D. Cody, M.L. Fogel, R.M. Hazen, R.J. Hemley, and W.T. Huntress, "Microbial Activity at Gigapascal Pressures," Science 295: 1514-1516, 2002
 V.R. Baker, "Water and the Martian Landscape," Nature 412: 228-236, 2001.
 M.G. Kivelson, K.K. Khurana, C.T. Russell, M. Volwerk, R.J. Walker, and C. Zimmer,"Galileo Magnetometer Measurements: A Stronger Case for a Subsurface Ocean at Europa," Science 289: 1340-1341, 2000.
 R. Meier, B.A. Smith, T.C. Owen, and R. Terrile, "The Surface of Titan from NICMOS Observations with the Hubble Space Telescope," Icarus 145: 462-473, 2000.
 S.J. Mojzsis, G Arrhenius, K.D. McKeegan, T.M. Harrison, A.P. Nutman, and C.R.L. Friend, "Evidence for Life on Earth Before 3,800 Million Years Ago," Nature 384: 55-59, 1996.
 S.J. Mojzsis, T.M. Harrison, and R.T. Pidgeon, "Oxygen-Isotope Evidence from Ancient Zircons for Liquid Water at the Earth’s Surface 4,300 Myr Ago," Nature 409: 178-181, 2002.
 N.R. Pace, "A Molecular View of Microbial Diversity and the Biosphere," Science 276: 734-740, 1997.
 S.J. Butcher, J.M. Grimes, E.V. Makeyev, D.H. Bamford, and D.I. Stuart, "A Mechanism for Initiating RNA-Dependent RNA Polymerization," Nature 410: 235-240, 2001.