cosmic environments and to date is almost completely unexplored. High sensi- 

 tivity, in addition to good spatial and spectral resolution, will be extremely 

 important, as will the laboratory and theoretical studies needed to correctly 

 interpret the new observational data. 



6.1.1 Detection of Extrasolar Planetary Systems 



The best opportunity for conducting a systematic survey of the nearest stars 

 for massive, long-period planets is a dedicated astrometric telescope to be 

 mounted on the upper boom of the Space Station. Alternative approaches such 

 as searches for short-period planets will require technical breakthroughs to 

 develop a double differential photometer, or a long-lived platform to monitor 

 thousands of stars for periodic occultations may be accommodated by Space 

 Station. The detection of extrasolar planetary systems is best pursued at optical 

 and near-infrared wavelengths. Earth-orbital observations are crucial as the 

 Earth's atmosphere imposes severe limitations on the ability to either directly 

 detect a planetary companion to a star or to indirectly deduce the presence of a 

 planet from its influence on the stellar motion or apparent brightness. While the 

 HST will be able to measure, with observations taking minutes, the relative 

 position of a nearby star that is as accurate as can be obtained with modern 

 detectors and hours of ground-based telescope time, and it will have the orbital 

 longevity and mechanical stability needed for such an astrometric search pro- 

 gram, it is unlikely that sufficient time will be allocated for a systematic search 

 for extrasolar planetary systems. 



The logical followup to an astrometric detection of an extrasolar planet is its 

 direct detection. Once again, this is best done from observatories in Earth orbit. 

 The HST will provide the best opportunity in the near term to attempt imaging 

 any extrasolar planets detected astrometrically or tentatively identified from 

 ground-based observations. Imaging is easier at near-infrared wavelengths where 

 the contrast ratio of planet and star is larger and either the NICMOS infrared 

 spectrometer or the imaging Michelson interferometer selected for the second 

 generation of HST instrumentation may provide a capability to do just that. If 

 either SI RTF or ISO prove to be capable of producing a "superresolution," 

 they may be able to image the outer planets around nearby stars. FIRST or LDR 

 should eventually provide the necessary better resolution, but a free-flying infra- 

 red interferometer will be required to provide imaging capabilities for more 

 distant stars. 



6.1.2 The Solar Nebula and its Analogs 



Observations of regions of star formation are important to exobiology in two 

 ways. First, they will determine how stars hospitable to the origin of life are 



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