HISTORY OF LIFE DETECTION APPROACHES

Gerald A. Soffen

Goddard Space Flight Center

National Aeronautics and Space Administration

Abstract

The history of life detection (search for extraterrestrial life) began with the invention of the telescope. Astronomer Perceval Lowell stimulated public interest in the canals of Mars from his personal observations. With the advent of the National Aeronautics and Space Administation (NASA) in 1958, the search for extraterrestrial life became a U.S. national priority. Telescopic and spectroscopic observations were made of planets and interstellar space for detection of evidence for life in the 1960s. The development of numerous in situ instruments was supported by NASA in the period 1960-1975. These involved detection of form, function, and chemistry. The Viking experiments to Mars in 1976 carried numerous instruments and performed observations and experiments on the surface and atmosphere to directly detect living organisms or their organic products or debris. Terrestrial meteorites that have been recovered have been examined for possible signs of life. The Search for Extraterrestrial Intelligence (SETI) program has been listening for coherent radiation, searching for signals from other technological civilizations.

Introduction

NASA was initiated in 1958, in response to the Soviets having launched their Sputnik. On May 21, 1961, President Kennedy announced a decision to “put a man on the Moon before the end of the decade,” despite the urgings of a number of U.S. scientists who were arguing for instrumented planetary missions. Homer Newell headed the first Space Science Office (OSS) and realized the needs of the new agency to invoke some practical as well as pure biology into the program. “NASA, (is) concerned with life sciences in a variety of ways . . . medical support for manned spaceflight, . . . life support systems, . . . aviation medicine . . . [and] exobiology (the search for and the study of extraterrestrial life) . . . Only space biology and exobiology could be regarded as pure science . . . ” is quoted from a chapter entitled “Life Sciences: No Place in the Sun” in Newell's book on the history of space science. The decade of the 1960s was used by the exobiologists mostly to develop techniques of life detection.

Life Detection

The exobiologists agreed that Mars is the most likely planet in the solar system, other than the Earth, to support living organisms, and that if there was any martian life it would most likely be microbial in nature. At that time, there was serious attention to what was called “the wave of darkening” on Mars, which some planetologists interpreted as possible biological microorganisms that were quiescent during the dry part of the season and became active when water became available. Another spectroscopic observation was the “Sinton Bands,” absorption at 3.58 µm and 3.69 µm, which suggested possible organic material; the bands were subsequently discovered to be caused by deuterium in the Earth's atmosphere.

Wolf Vishniac is credited to be the first to invent a device for monitoring microbial growth on another planet. Under a NASA grant in 1961, Vishniac built a laboratory model of a machine that would self-inoculate a small soil sample into liquid growth media. This was illuminated, and the subsequent increase in the number of organisms was measured by the changing opacity of the growing inoculation. This technique of measuring cloudiness by forward light scattering (nephelometry) to measure growth rate had been previously shown. Changes in pH as a function of time were also measured. The device called the “Wolf Trap” was developed and field-tested on Earth, but was not included onboard the Viking missions that landed the first life detection experiments on Mars in 1976.

Another life detection instrument funded by NASA utilized a radioactive tracer, 14C, to measure the respiratory products of a growing culture of microorganisms. Gilbert Levin, having used this technique for the rapid



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