The astrobiology primer: An outline of general knowledge - Version 1, 2006

Peer reviewe

The Stellar Imager (SI) "Vision Mission"

The Stellar Imager (SI) is a Vision Mission in the Sun-Earth Connection (SEC) NASA Roadmap, conceived for the purpose of understanding the effects of stellar magnetic fields, the dynamos that generate them, and the internal structure and dynamics of the stars in which they exist. The ultimate goal is to achieve the best possible forecasting of solar/stellar activity and its impact on life in the Universe. The science goals of SI require an ultra-high angular resolution, a t ultraviolet wavelengths, on the order of 100 micro-arcsec and baselines on the order of 0.5 km. These requirements call for a large, multi-spacecraft (>20) imaging interferometer, utilizing precision formation flying in a stable environment, such as in a Lissajous orbit around the Sun-Earth L2 point. In this paper, we present an update on the ongoing SI mission concept and technology development studies

An Optical/UV Space Coronagraph Concept for the

NASA's current strategic plan calls for the launching of a space observatory, The Terrestrial Planet Finder (TPF), by the middle of the next decade; it will search for terrestrial planets in the habitable zone of roughly 150 nearby stars and characterize them for the potential to harbor life. This paper describes a visible light concept for TPF developed by the Ball Aerospace led TPF study team. This concept consists of a 4 meter by 10 meter coronagraphic telescope in a deep space orbit. Imaging planets requires overcoming the problem of high contrast between the light from the parent star and from the planet, coupled with their small angular separation. For a coronagraph, the di#raction pattern of the telescope must be suppressed at the planet image location. The high contrast needed can be achieved using optimized pupil shapes that provide the needed 10 billion times suppression as close as 4#/D to the center of the star. In addition, wavefront errors induced by the mirror deformities will be corrected using deformable mirrors in a novel active optics system that corrects both amplitude and phase errors. The paper describes the baseline design of a visible light telescope and instrument that will meet the mission requirements

A Re-appraisal of the Habitability of Planets Around M Dwarf Stars

Stable, hydrogen-burning, M dwarf stars make up about 75% of all stars in the Galaxy. They are extremely long-lived, and because they are much smaller in mass than the Sun (between 0.5 and 0.08 M-sun), their temperature and stellar luminosity are low and peaked in the red. We have re-examined what is known at present about the potential for a terrestrial planet forming within, or migrating into, the classic liquid-surface-water habitable zone close to an M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially habitable, wet planets that reside within their habitable zones, which are only about one-fifth to 1/50(th) of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 M-Earth orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone does not necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geother mal activity or thermal and nonthermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life. This paper presents the summary conclusions of an interdisciplinary workshop (http://mstars.seti.org) sponsored by the NASA Astrobiology Institute and convened at the SETI Institute