September 23, 1997
We'll probably know within the next 20 years, Neville J. Woolf said last week in Tucson in the first Steward Public Evening Lecture for 1997-98. Woolf, professor of astronomy at The University of Arizona in Tucson, is part of the Terrestrial Planet Finder project for the NASA Origins program. The focus of the project is detecting extra-solar planets which are hospitable to life.
There are several factors which make the detection of Earth-like planets a difficult enterprise. Perhaps the most obvious difficulty is the enormous distance between the Earth and planets well beyond our solar system: the further away a planet is, the fainter the image of it will be. Another difficulty results from the planet's proximity to its star. Because of its brightness, the host star far outshines the nearby planet. In our solar system, for instance, the planets are ten million times dimmer than the sun. A third difficulty lies in the detection of life on these planets: which gases provide evidence of life?
In association with other UA astronomers, including Roger Angel and James Burge of the Steward Observatory, Woolf has proposed the construction of a linear nulling interferometer for the detection of earth-like planets. A linear nulling interferometer is essentially a four-mirror device that determines planetary position, atmospheric emission spectrum and surface temperature. Two larger mirrors are aligned with two smaller, peripheral mirrors for the detection of radiation. The mirrors, because of their arrangement, block out, or "null," the light from a star in order to examine the surrounding space for earth-like planets. To map the positions of planets and determine the spectrum produced by their atmospheres, the device separates the bands of the spectrum and maps the sky in each band. It also measures surface temperature. In particular, the linear nulling interferometer will search for the presence of carbon dioxide, ozone and water in the planetary atmosphere. The substantial presence of all three on a planet of earth-like temperature is fairly good indication of the existence of microorganisms.
Woolf noted that the technology needed for this project is similar to the technology for the Next Generation Space Telescope, so the proposed date for construction of the Terrestrial Planet Finder project in 2005 is feasible and may even be earlier. Speedy development depends upon an efficient means of propulsion into space and an improvement in mirror technology, Woolf said. The focus has been on smaller, thinner mirrors which cost only a fraction of the Hubble Space Telescope mirror. Steward Observatory astronomers' recent attempts to produce small-scale models have been successful, he added.
The Terrestrial Planet Finder project is not important for astronomers only, Woolf emphasized. Biologists, for example, would have a keen interest in the project if life was discovered on an extra-solar planet. As NASA Administrator Dan Goldin said it, "No human endeavor and no human thought would be untouched by that discovery."
Web sites:
Origin Mission: The Terrestrial Planet Finder
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