doi:10.1016/j.endeavour.2006.02.005
Published by Elsevier Ltd.
NASA and the search for life in the universe
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Steven J. Dicka, 
aNASA HQ, 300 E Street SW, Washington, DC 20546, USA
Available online 3 April 2006.
Almost from its beginnings in 1958, the National Aeronautics and Space Administration (NASA) set up a life-science program. Because one of the priorities of the organization is to search for life beyond Earth, NASA began designing spacecraft to unravel the mysteries of Mars. The effort to search for life on Mars culminated in the landing of two Viking spacecraft on the surface of the planet in 1976. Although the biology experiments conducted as part of these missions provided some evidence for the possibility of life, the scientific consensus was that they drew a blank. In 1996, however, the ‘Mars rock’ rekindled interest in life in our solar system. The discovery of an ocean on the Jovian moon Europa, of organic molecules on the Saturnian moon Titan and persuasive evidence that water once flowed on Mars suggests that the solar system is still of considerable exobiological interest. In addition, since 1995 approximately 175 planets have been found beyond our solar system. Although these discoveries are gas giants, NASA spacecraft might soon detect Earth-sized planets. The search for life in the universe continues.
Figure 1. Image taken from the Viking 2 of the Utopian Plain on Mars. The boulder-strewn field of red rocks reaches to the horizon nearly two miles from Viking 2. Scientists believe the colors of the Martian surface and sky in this photo represent their true colors. Fine particles of red dust have settled on the surface of the spacecraft. The salmon color of the sky is caused by dust particles suspended in the atmosphere. Color calibration charts for the cameras are mounted at three locations on the spacecraft. Note the blue star field and red stripes of the American flag. The circular structure at top of the image is the high-gain antenna, pointed toward Earth. Viking 2 landed on Mars on 3 September 1976, some 4600 miles from its twin, Viking 1, which touched down on 20 July 1976. Image courtesy of NASA.
Figure 2. High resolution scanning electron microscope image showing unusual tube-like structure less than 1/100th the width of a human hair that were found in Martian meteorite ALH 84001. Some have interpreted this to be evidence of past life on Mars, and the ensuing controversy demonstrates the difficulties of data interpretation. Image courtesy of NASA.
Figure 3. A NASA Hubble Space Telescope image of a region of the Great Nebula in Orion. The Orion Nebula star-birth region is 1500 light years away, and one of the nearest regions of very recent star formation (300 000 years ago). The nebula is a giant gas cloud illuminated by the brightest of the young hot stars at the top of the picture. Many of the fainter young stars are surrounded by disks of dust and gas that are slightly more than twice the diameter of the Solar System. The great plume of gas in the lower left in this picture is the result of the ejection of material from a recently formed star. The image was taken on 29 December 1993 with the Wide Field and Planetary Camera 2 of the Hubble Space Telescope. Image reproduced courtesy of C.R. O'Dell, Rice University and NASA.
Figure 4. Cosmic evolution. The upper left portion of this image shows the formation of stars, the production of heavy elements and the formation of planetary systems, including our own. On the left prebiotic molecules, RNA and DNA are formed while the Earth is still primitive, within the first billion years of its existence. At center the origin and evolution of life leads to increasing complexity, culminating with astronomers at upper right contemplating the universe! The image was created by David DesMarais, Thomas Scattergood and Linda Jahnke at NASA Ames in 1986 and reissued in 1997. Image courtesy of NASA.
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