The astronomical detection of biosignatures on extrasolar terrestrial planets: the Virtual Planetary Laboratory
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astrobiology extrasolar planets remote sensing↗
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The astronomical detection of biosignatures on extrasolar terrestrial planets: the Virtual Planetary Laboratory
Explore the source record for details and available documents.
astrobiology extrasolar planets remote sensing↗
Magnetosphere Emissions from Extrasolar Planets: Present and Future Prospects
No abstract available
habitability of planets↗
Discrete extrasolar X-ray sources.
Galactic X ray sources observed in EM spectrum high energy region, discussing hot plasma cloud thermal radiation and electrons synchrotron radiation as emission sources
Rossi, B. B.↗
Photometric detection of extrasolar planets using L.S.T.-type telescopes
Detection of planets similar to the earth and Jupiter that might be circling nearby stars is possible with the large space telescope (LST), or modifications of this instrument. The use of the moon as an occulter to increase the signal-to-noise ratio and the expected photon fluxes from hypothetical planetary companions to alpha Centauri A and B, tau Ceti, and epsilon Eridani are discussed. Because Barnard's Star is a red dwarf of visual apparent magnitude 9.5, photometric detection of its hypothetical Jupiter-like companion would be difficult using the LST-occulter system described in this paper.
Fennelly, A. J.↗
Detection of extrasolar planets by the large deployable reflector
The best wavelength for observing Jupiter-size planetary companions to stars other than the Sun is one at which a planet's thermal emission is strongest; typically this would occur in the far-infrared region. It is assumed that the orbiting infrared telescope used is diffraction-limited so that the resolution of the planet from the central star is accomplished in the wings of the star's Airy pattern. Proxima Centauri, Barnard's Star, Wolf 359, and Epsilon Eridani are just a few of the many nearest main-sequence stars that could be studied with the large deployable relfector (LDR). The detectability of a planet improves for warmer planets and less luminous stars; therefore, planets around white dwarfs and those young planets which have sufficient internal gravitational energy release so as to cause a significant increase in their temperatures are considered. If white dwarfs are as old as they are usually assumed to be (5-10 billion yr), then only the nearest white dwarf (Sirius B) is within the range of LDR. The Ursa Major cluster and Perseu cluster are within LDR's detection range mainly because of their proximity and young age, respectively.
Hollenbach, D. J.↗
Detectability of extrasolar planetary transits
Precise stellar photometry can be used to detect other planetary systems. However, the intrinsic variability of stellar luminosity imposes a fundamental limit on the sensitivity of this method. Based on recent precise solar observations made from the Solar Maximum Mission satellite, it appears that the detection of earth-sized planets will be marginal during periods of high stellar activity. However, with a suitable photometer larger planets should be readily detectable even in the presence of stellar activity equal to that of the sun at the peak of its sunspot cycle. The high precision, multiple-star photometric system required to detect planets in other stellar systems could be used to monitor flares, starspots, and global oscillations.
Borucki, W. J.↗
The radial velocity search for extrasolar planets
Stars are observed with a ground-based instrument designed to measure small changes in the line-of-sight velocities. The purpose of the observations is to detect large planets by the oscillatory reflex motion they induce on the stars they are orbiting. The instrument is an optical spectrometer for which wavelengths are first calibrated by transmission through a tunable Fabry-Perot etalon interferometer. Changes in the line-of-sight velocities are revealed by changes in the Doppler shift of the absorption-line spectra of stars. The scrambling of incident light by an optical fiber and the stability of wavelength calibration by a tilt-tunable Fabry-Perot etalon provide immunity to systematic errors that historically have effected more conventional radial velocity spectrographs. A cross-dispersed echelle spectrograph spatially separates the orders of constructive interference transmitted through the etalon. Selecting several echelle diffraction orders in the vicinity of 4250 to 4750 A, which are imaged on a CCD, about 350 points on the profile of the stellar spectrum are sampled by successive orders of interferometric transmission through the etalon.
Mcmillen, R. S.↗
The radial velocity search for extrasolar planets
Researchers are measuring small changes in the line-of-sight velocities of stars to detect the oscillating reflex acceleration induced by large planets. The intention is to observe enough stars for a long enough time to be able to make a statement of the probability of planets in a certain range of masses even if no planetary perturbations are detected. To make these measurements of Doppler shift with the required sensitivity, a new instrument was specifically designed, built and tested for this campaign of ground-based planet detection. The instrument is an optical spectrometer for which wavelengths are first calibrated by transmission through a tunable Fabry-Perot etalon interferometer. The intrinsic stability of the etalon and an image-scrambling fiber optic light feed provide great sensitivity to line-of-sight accelerations and immunity to systematic errors.
Mcmillen, Robert S.↗
Infrared imaging of extrasolar planets
An optical system for direct detection, in the infrared, of planets orbiting other stars is described. The proposed system consists of a large aperture (about 16 m) space-based telescope to which is attached a specialized imaging instrument containing a set of optical signal processing elements to suppress diffracted light from the central star. Starlight suppression is accomplished using coronagraphic apodization combined with rotational shearing interferometry. The possibility of designing the large telescope aperture to be of a deployable, multiarm configuration is examined, and it is shown that there is some sacrifice in performance relative to a filled, circular aperture.
Diner, David J.↗
The radial velocity search for extrasolar planets
Radial velocity measurements are being made to search for planets orbiting stars other than the Sun. The reflex acceleration induced on stars by planets can be sensed by measuring the small, slow changes in the line-of-site velocities of stars. To detect these planetary perturbations, the data series must be made on a uniform instrumental scale for as long as it takes a planet to orbit its star. A spectrometer of extreme stability and unprecedented sensitivity to changes in stellar radial velocities was operated.
Mcmillan, Robert S.↗
Gamma-ray burst constraints on the galactic frequency of extrasolar Oort Clouds
With the strong Compton Gamma-Ray Observatory/Burst and Transient Source Experiment (CGRO/BATSE) evidence that most gamma-ray bursts do not come from galactic neutron stars, models involving the accretion of a comet onto a neutron star (NS) no longer appear to be strong contenders for explaining the majority of bursts. If this is the case, then it is worth asking whether the lack of an observed galactic gamma-ray burst population provides a useful constraint on the number of comets and comet clouds in the galaxy. Owing to the previously unrecognized structural weakness of cometary nuclei, we find the capture cross sections for comet-NS events to be much higher than previously published estimates, with tidal breakup at distances R(sub b) approx. equals 4 x 10(exp 10) cm from the NS. As a result, impacts of comets onto field NSs penetrating the Oort Clouds of other stars are found to dominate all other galactic NS-comet capture rates by a factor of 100. This in turn predicts that if comet clouds are common, there should be a significant population of repeater sources with (1) a galactic distribution, (2) space-correlated repetition, and (3) a wide range of peak luminosities and luminosity time histories. If all main sequence stars have Oort Clouds like our own, we predict approximately 4000 such repeater sources in the Milky Way at any time, each repeating on time scales of months to years. Based on estimates of the sensitivity of the CGRO/BATSE instrument and assuming isotropic gamma-ray beaming from such events, we estimate that a population of approximately 20-200 of these galactic NS-Oort Cloud gamma-ray repeater sources should be detectable by CGRO. In addition, if giant planet formation is common in the galaxy, we estimate that the accretion of isolated comets injected to the interstellar medium by giant planet formation should produce an additional source of galactic, nonrepeating, events. Comparing these estimates to the 3-4 soft gamma-ray repeater sources detected by BATSE, one is forced to conclude that (1) comet impacts on NSs are inefficient at producing gamma rays; or (2) the gamma rays from such events are highly beamed; or (3) the fraction of stars in the galaxy with Oort Clouds like our own is not higher than a few percent.
Shull, J. Michael↗
Photon-Weighted Midpoint Exposure Meter for Keck/HIRES Extrasolar Planet Research
NASA Grant was received for research involving the construction of a photon-weighting midpoint exposure meter for the Keck HIRES spectrometer, and for support of our NASA/Keck-based planet research with this instrumentation. The research funds were also to be used to make our iodine cell calibration system and exposure meter available to the NASA Keck observing community. Progress this past year, the second of the 3-year granting period, involved work in 4 areas: 1) Further construction of the midpoint exposure meter. 2) Assisting observers with use of the Iodine system. 3) Acquisition of precision radial velocity data on our program star sample with continued monitoring to proceed in subsequent years as available telescope time permits. 4) Reduction and analysis of incoming precision radial velocity data to reject problematic and uninteresting program stars, and to identify promising planet candidates.
Source record↗
End-to-End System Test of the Relative Precision and Stability of the Photometric Method for Detecting Earth-Size Extrasolar Planets
We developed the CCD camera system for the laboratory test demonstration and designed the optical system for this test. The camera system was delivered to Ames in April, 1999 with continuing support mostly in the software area as the test progressed. The camera system has been operating successfully since delivery. The optical system performed well during the test. The laboratory demonstration activity is now nearly complete and is considered to be successful by the Technical Advisory Group, which met on 8 February, 2000 at the SETI Institute. A final report for the Technical Advisory Group and NASA Headquarters will be produced in the next few months. This report will be a comprehensive report on all facets of the test including those covered under this grant. A copy will be forwarded, if desired, when it is complete.
Dunham, Edward W.↗
Searching for Extrasolar Planets with SIM
The Space Interferometry Mission (SIM) will be the first spacebased long base-line Michelson interferometer designed for precision astrometry. SIM will extend the reach of astrometry to cover the entire Galaxy, and will address a wide range of problems in Galactic structure and stellar astrophysics. It will also serve as a technology precursor for future astrophysics missions using interferometers. SIM will be a powerful tool for discovering planets around nearby stars, through detection of the reflex motion, and it will directly measure masses for the planets detected this way. It will have a single-measurement precision of 1 microarcsecond in a frame defined by nearby reference stars, enabling SIM to search for planets with masses as small as a few earth masses around the nearest star. More massive planets will be detectable to much larger distances.
Unwin, Stephen C.↗
Delivery of Volatiles to Habitable Planets in Extrasolar Planetary Systems
The Earth can support life because: (1) its orbit lies in the Sun's habitable zone', and (2) it contains enough volatile material (e.g. water and organics) for life to flourish. However, it seems likely that the Earth was drier when it formed because it accreted in a part of the Sun's protoplanetary nebula that was too hot for volatiles to condense. If this is correct, water and organics must have been delivered to the habitable zone, after dissipation of the solar nebula, from a 'wet zone' in the asteroid belt or the outer solar system, where the nebula was cool enough for volatiles to condense. Material from the wet zone would have been delivered to the Earth by Jupiter and Saturn. Gravitational perturbations from these giant planets made much of the wet zone unstable, scattering volatile-rich planetesimals and protoplanets across the Solar System. Some of these objects ultimately collided with the inner Planets which themselves lie in a stable part of the Solar System. Giant planets are now being discovered orbiting other sunlike stars. To date, these planets have orbits and masses very different from Jupiter and Saturn, such that few if any of these systems is likely to have terrestrial planets in the star's habitable zone. However, new discoveries are anticipated due to improved detector sensitivity and the increase in the timespan of observations. Here we present numerical experiments examining the range of giant-planet characteristics that: (1) allow stable terrestrial Planets to exist in a star's habitable zone, and (2) make a large part of the star's wet zone weakly unstable, thus delivering volatiles to the terrestrial planets over an extended period of time after the dissipation of the solar nebula.
Chambers, John E.↗
Model Atmospheres and Spectra for Extrasolar Giant Planets
In the past few years much new observational data has become available for brown dwarfs and extra solar planets. Not only are new objects being discovered but the availability of higher resolution spectra is improving. This allows a better comparison between the models and the available data, and places new constraints on the models which now have to be made more physically realistic in order to better interpret the observations. Under this grant, an array of new opacities were calculated and successfully applied to a variety of physical situations that were used as input to model available observations of brown dwarfs and extra solar giant planets.
Freedman, Richard S.↗