The Search for Life's Origins Progress and Future Directions in Planetary Biology and Chemical Evolution (1990) / Chapter Skim
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6. Search for Life Outside the Solar System
6. Search for Life Outside the Solar System
Pages 105-122
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From page 105... ...
More recently, the microwave signals generated by human technology could provide that same remote observer with circumstantial evidence for the existence of some form of intelligence on the planet Earth. These two examples of life detection should apply to other planets as well.
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From page 106... ...
The underlying scientific goal in searching for life beyond the solar system is the same as the goal of the Viking biology experiments on Mars or the study of astrophysical influences on the evolution of life on the planet Earth. As described in previous chapters, there are compelling reasons to look for evidence of the origin of life on Mars during a more clement epoch of that planet's history.
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From page 107... ...
To escape from this dilemma, those other systems must be found in order to achieve the fundamental goal of understanding the distribution of life in the universe. The basic techniques for detecting extrasolar planets are well understood (a detailed discussion of this subject is given in reports of the SSB, 1988a,b)
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From page 108... ...
These searches for deliberately generated signals should be complemented by searches for other indirect manifestations of a distant technology. Although the two approaches to searching for life beyond the solar system can provide very useful inputs to each other, they may be pursued independently and simultaneously at a pace set by the rate of maturation of the requisite technologies.
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From page 109... ...
There are a number of Earth-orbital telescopes for infrared and submillimeter observations under design, or in the planning stage, but as currently conceived, none will provide the resolution of 0.01 to 0.1 arc see necessary to observe dimensions corresponding to our planetary system within distant protostellar nebulae. The recent study Space Science in the Twenty-First Century (SSB, 1988b)
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From page 110... ...
The actual surface temperature of any particular planet will depend upon the abundances and chemical nature of its atmospheric constituents as well as its distance from the host star. Obtaining information on surface temperature and the chemical composition of an atmosphere requires direct imaging and spectroscopic analyses of each distant planet body.
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From page 111... ...
For these studies, therefore, it is important to continue the development of technologies for supersmooth mirror production, low-lightscattering telescopes, and large-orbital infrared, submillimeter, and optical telescopes that may eventually permit the direct imaging and gross atmospheric characterization of distant planets. OBJECTIVE 3: To search for presumptive evidence of life in other planetary systems.
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From page 112... ...
The examination of distant planets first requires the identification of such planets, but searches for other technologies can be made in the direction of plausible targets without a priori knowledge of the existence of a suitable planetary abode. Furthermore, searches can also be indiscriminate with respect to direction if the technology of another advanced civilization is sufficiently "loud." Thus, several different search strategies, based on different concepts of what constitute the most detectable features of a distant technology, may have to be employed in conducting an exhaustive search for signs of extraterrestrial technology.
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From page 113... ...
2. Spectroscopic detection: The same wobble in the star's motion induced by a star and planet orbiting about their common center of mass can be seen spectroscopically if the plane of the orbits is nearly parallel to the line of sight.
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From page 114... ...
3. Photometric detection: Astrometric and spectroscopic detection schemes have a long history, and both have recently benefited from a new generation of instrumentation; The next generation or two of astronomical instrumentation may enable a third detection scheme.
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From page 115... ...
However, this factor of improvement in diffracted light can be utilized only if the scattering due to figure error in the primary mirror and to surface dust or scratches is at least 1000 times less than the diffraction of a conventional mirror. Supersmooth mirrors have been manufactured for use in the fabrication of microelectronics.
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From page 116... ...
Studying Nebulae and Disks The study of protoplanetary nebulae and young stellar disk systems also requires direct imaging techniques. Estimates of the required measurement accuracies for studying solar-system-scale objects at 10 parsecs or at 140 parsecs (Taurus molecular cloud star-forming region)
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From page 117... ...
The search for primitive life may not yet be timely, but the development of technology to meet required measurement accuracies is. The problem of finding life beyond the solar system may become more tractable if there exist extraterrestrial technologies engaged in activities that can be detected remotely.
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From page 118... ...
should occupy most of the decade to be covered by this document. The measurement accuracy appropriate for such a search strategy may be determined by establishing the sensitivity required to detect the artificial microwave signals generated by current terrestrial technology, if the planet Earth was assumed to be located across the Milky Way galaxy from us.
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From page 119... ...
The planned microwave search is restricted to the lower portion of the window by the increased atmospheric noise inherent to any terrestrial ground-based search. Future searches will require access to space to extend the search to higher frequencies and to escape the increasing interference generated by terrestrial communication technology.
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From page 120... ...
Innovations, breakthroughs, and perhaps completely new technologies are required to directly image terrestrial planets, perform chemical assays TABLE 6.1 Instruments for the Detection of Extrasolar Planets: Astrometric Methods Resolution Telescope/Spacecraft Launch Instrument (arc see) Allegheny Observatory Now MAP 10-3 Lick Observatory Now Image detector 10-3 Hubble Space Telescope 1990 WFC 10-3 FGS 1 0-3 Dedicated new ?
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From page 121... ...
0.5 10-4 interferometer Optical ? 0.3 10~~° interferometer NOTE: CCD = charge coupled device; CIT = Circumstellar Imaging Telescope; FIRST = Far-Infrared Space Telescope; FOS = faint-object spectrograph; HIMS = Hubble imaging Michelson spectrometer; IR = infrared; ISO = Infrared Space Observatory; ISOCAM = Infrared Space Observatory camera; LDR = large deployable reflector; MIPS = multiband imaging photometer; NICMOS = near-infrared camera and multiobject spectrometer; SIRTF = Space Infrared Telescope Facility.
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From page 122... ...
Sky Survey All-sky coverage 0.3 to 3 s of observation per beam at each frequency band 1- to 110-GHz frequency coverage Dual circular polarization Moderate resolution and sensitivity Primary sensitivity to CW signals RFI data base 15 million channels (30-Hz and 74-kHz resolution bandwidths) thereon, search for leakage radiation throughout the galaxy, and move the search for extraterrestrial technologies to higher frequencies or to other search concepts.
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