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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

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.↗
NASA NTRS1991

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.↗
NASA NTRS1991

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.↗
NASA NTRS1995

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↗
NASA NTRS1999

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↗
NASA NTRS2000

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.↗
NASA NTRS2000

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.↗
NASA NTRS2000

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.↗
NASA NTRS2000

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.↗
NASA NTRS2001

Short-Term Dynamical Interactions Among Extrasolar Planets

We show that short-term perturbations among massive planets in multiple planet systems can result in radial velocity variations of the central star which differ substantially from velocity variations derived assuming the planets are executing independent Keplerian motions. We discuss two alternate fitting methods which can lead to an improved dynamical description of multiple planet systems. In the first method, the osculating orbital elements are determined via a Levenberg-Marquardt minimization scheme driving an N-body integrator. The second method is an improved analytic model in which orbital elements such as the periods and longitudes of periastron are allowed to vary according to a simple model for resonant interactions between the planets. Both of these methods can potentially determine the true masses for the planets by eliminating the sin(i) degeneracy inherent in fits that assume independent Keplerian motions. As more radial velocity data is accumulated from stars such as GJ876, these methods should allow for unambiguous determination of the planetary masses and relative inclinations.

Laughlin, Gregory↗
NASA NTRS1999

Planetary Formation: From The Earth And Moon To Extrasolar Planets

An overview of current theories of planetary growth, emphasizing the formation of habitable planets, is presented. These models are based upon observations of the Solar System and of young stars and their environments. They predict that rocky planets should form around most single stars, although it is possible that in some cases such planets are lost - to orbital decay within the protoplanetary disk. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth like terrestrial planets, but if they become massive enough before the protoplanetary disk dissipates, then they are able to accumulate substantial amounts of gas. Specific issues to be discussed include: (1) how do giant planets influence the formation and habitability of terrestrial planets? (2) could a giant impact leading to lunar formation have occurred - 100 million years after the condensation of the oldest meteorites?

Lissauer, Jack J.↗
NASA NTRS2002

Origins of Solar Systems: Removing Activity-Related Radial Velocity Noise To Improve Extrasolar Planet Searches

We have continued the super high resolution (R is approximately 200,000), high S/N ((greater than) 300) echelle study of joint line bisector and radial velocity variations using the McDonald 2-D (two dimensional) coude. Observing runs in October 2000 and March 2001 were plagued by poor weather, but runs in June and October 2001 were good. We have made a preliminary analysis of the limited data in hand, and find some tantalizing evidence for correlations between median line bisector displacement and radial velocity v (sub r). The correlation appears to be specific to the particular star being considered, probably since it is a function of both spectral type and rotation rate.

Saar, Steven↗
NASA NTRS1999

Planetary Formation: From the Earth and Moon to Extrasolar Giant Planets

An overview of current theories of star and planet formation is presented. These models are based upon observations of the Solar System and of young stars and their environments. They predict that rocky planets should form around most single stars, although it is possible that in some cases-such planets are lost to orbital decay within the protoplanetary disk. The frequency of formation of gas giant planets is more difficult to predict theoretically. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth like terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. Specific issues to be discussed include: (1) how large a solid core is needed to initiate rapid accumulation of gas? (2) can giant planets form very close to stars? (3) could a giant impact leading to lunar formation have occurred approx. 100 million years after the condensation of the oldest meteorites?

Lissauer, Jack J.↗
NASA NTRS1999

Planetary Formation: From the Earth and Moon to Extrasolar Giant Planets

An overview of current theories of star and planet formation is presented. These models are based upon observations of the Solar System and of young stars and their environments. They predict that rocky planets should form around most single stars, although it is possible that in some cases such planets are lost to orbital decay within the protoplanetary disk. The frequency of formation of gas giant planets is more difficult to predict theoretically. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth like terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. Specific issues to be discussed include: (1) how large a solid core is needed to initiate rapid accumulation of gas? (2) can giant planets form very close to stars? (3) could a giant impact leading to lunar formation have occurred approximately 100 million years after the condensation of the oldest meteorites?

Lissauer, Jack↗
NASA NTRS2003

Origins of Solar Systems: Removing Activity-Related Radial Velocity Noise to Improve Extrasolar Planet Searches

We have continued the super high resolution (R is approximately 200,000), high S/N (> 300) echelle study of joint line bisector and radial velocity variations using the McDonald 2-D coude. A long observing run in October 2002 was quite successful (8 clear nights). We now have close to three years of data, which begins to sample a good fraction of the magnetic cycle timescales for some of our targets (e.g., K Ceti; P(sub cyc)=5.6 yrs). This will be very helpful in unraveling the complex relationships between plage and v(sub r), changes which we have uncovered. A preliminary analysis of the limited data in hand, and find some tantalizing evidence for correlations between median line bisector displacement and radial velocity v(sub r). The correlation appears to be specific to the particular star being considered, probably since it is a function of both spectral type and rotation rate. Additional information regarding progress on the grant is included.

Saar, Steven↗
NASA NTRS2003

The Formation of Life-sustaining Planets in Extrasolar Systems

The spatial exploration is providing us a large quantity of information about the composition of the planets and satellites crusts. However, most of the experiences that are proposed in the guides of activities in Planetary Geology are based exclusively on the images utilization: photographs, maps, models or artistic reconstructions [1,2]. That things help us to recognize shapes and to deduce geological processes, but they says us little about the materials that they are implicated. In order to avoid this dicotomy between shapes and materials, we have designed an experience in the one which, employing of rocks and landscapes of our geological environment more next, the pupils be able to do an exercise of compared planetology analyzing shapes, processes and material of several planetary bodies of the Solar System.

Chambers, J. E.↗
NASA NTRS2003

Physical Studies of Brown Dwarfs and Extrasolar Planets

The primary activities supported under this grant included research into the mid-infrared spectral properties of brown dwarfs, with particular emphasis on the 3-4 micron region, the L band. Several observing trips were made to use facilities on Mauna Kea. The primary discovery was the detection of absorption due to CH4 in several L dwarfs, including one classified as an L5. This is significant since CH4 is usually considered to be the defining characteristic of T dwarfs. The stronger fundamental band at 3.3um, however, makes it possible to observe the emergence of CH4 at hotter temperatures. A secondary result of this work is the surprising weakness of the CH4 nu3 band. This can be interpreted as either an indication that derived effective temperatures are too low, or perhaps, that the equilibrium abundance of CH4 is suppressed due to non-equilibrium processes at work in the atmosphere.

Boyce, Joseph↗
NASA NTRS2004

Obliquity Variations of Extrasolar Terrestrial Planets

A planet's obliquity, which is the angle between its orbital angular momentum and its rotational angular momentum, is an important factor in determining its climate and habitability. For small obliquities, as well as obliquities close to 180 degrees, the planet receives more radiant energy from its star at equatorial latitudes than near its poles, whereas the poles are heated the most for obliquities near 90 degrees. Jacques Laskar has analyzed possible obliquity variations of the planets in our Solar System. His study also considers the same planets with different rotational periods, and the Earth without the Moon. He finds, using frequency map analysis, that the obliquity of the Earth is stabilized by the Moon, and can vary by at most a few degrees. In contrast, the obliquity of Mars can range from 0 to 60 degrees, and a hypothetical moonless Earth's axial tilt could be close to 0 degrees or as large as 85 degrees. Numerical integrations by Laskar and others have shown that Mars' obliquity indeed varies over most of its permitted range on time scales of tens of millions of years. In contrast, our analysis shows that the obliquity of a moonless Earth appears to be confined to the range of approximately 12 - 38 degrees over time scales of 100 million years. Results of ongoing longer integrations will be presented, and their implications discussed.

Lissauer, Jack J.↗