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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 649 records · Page 36
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NASA NTRS2001

Three Classes of Kuiper Belt Objects: Theory and Observations

As part of the Origins of Solar Systems program our team conducted a dynamically motivated search for three classes of Kuiper belt objects (distant comets near and beyond the orbit of Neptune). Our strategy has been to exploit variations in the sky density of Kuiper belt that result from the gravitational influence of Neptune. By searching two regions of the sky, one nearly 90 degrees from Neptune and one nearly opposite Neptune, and comparing the number of objects discovered in each region we are able to constrain the relative populations of resonant and non-resonant objects, a fundamental quantity in Kuiper belt formation models. In addition, by searching at a variety of angles above the plane of the solar system we have constrained the inclination distribution of Kuiper belt objects. We have conducted four searches for this program. One was in February 1999 and August 2000 at the Canada-France-Hawaii telescope (3.6-meter), and another was in May 1999 and Oct. 2000 at the Kitt Peak National Observatory (4-meter). In addition, a search for Uranian satellites was conducted.

Holman, Mathew J.↗
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 NTRS1993

Two searches for primeval galaxies

A number of active galaxies are now known at very large redshifts, some of them even have properties suggestive of galaxies in the process of formation. They commonly show strong Ly-alpha emission, at least some of which appears to be ionized by young stars. Inferred star formation rates are in the range approximately = 100-500 solar mass/yr. An important question is: are there radio-quiet, field counterparts of these systems at comparable redshifts? Whereas, we are probably already observing some evolutionary and formative processes of distant radio galaxies, the ultimate goal is to observe normal galaxies at the epoch when most of their stars form. We have, thus, started a search for emission-line objects at large redshifts, ostensibly young and forming galaxies. Our method is to search for strong line emission (hopefully Ly alpha) employing two techniques: a direct, narrow-band imaging search, using a Fabry-Perot interferometer; and a serendipitous long-slit spectroscopic search.

Thompson, D.↗
NASA NTRS1988

Chemical abundance of comets

Observations of NH2, (OI) and molecular ion spectra in comets represent virtually all of the volatile fraction of a comet nucleus. Their study leads to the N2, NH3, H2O, CO2, CO content of the nucleus, and thus to important constraints on models of comet formation and chemical processing in the primitive solar nebula. The observations of Comet Halley provide the opportunity for the first comprehensive determination of the abundances in a comet nucleus. The carbon isotope abundance ratio 12 C/13 C = 65 plus or minus 8 has been determined for Comet Halley from resolved rotational line structure in the CN B-X (0,0) band. The ratio is approximately 30 pct lower than the solar system value, 89, indicating either an enhancement of 13CN or a depletion of 12CN in the comet. Scenarios consistent with the observed carbon isotope ratio are: (1) formation of the comet at the periphery of the solar nebula in a fractionation-enriched 13CN region, or hidden from 12CN enrichment sources, and (2) capture of an interestellar comet. Long-slit charge coupled device (CCD) spectra obtained at the time of the spacecraft encounter of Comet Halley have also been analyzed. Scale lengths, production rates and column densities of CH, CN, C2 and NH2 were determined.

Wyckoff, Susan↗
NASA NTRS2007

The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

The Stellar Imager (SI) is a UV/Optical, Space-Based Interferometer designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and, via asteroseismology, stellar interiors and of the Universe in general. The ultra-sharp images of the Stellar Imager will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. SI's science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI's prime goal is to enable long-term forecasting of solar activity and the space weather that it drives. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. SI is included as a 'Flagship and Landmark Discovery Mission' in the 2005 NASA Sun Solar System Connection (SSSC) Roadmap and as a candidate for a 'Pathways to Life Observatory' in the NASA Exploration of the Universe Division (EUD) Roadmap (May, 2005). In this paper we discuss the science goals and technology needs of, and the baseline design for, the SI Mission (http://hires.gsfc.nasa.gov/si/) its ability to image the 'Biggest, Baddest, Coolest Stars'.

Carpenter, Kenneth↗
NASA NTRS1978

Invited papers presented to a workshop on thermodynamics and kinetics of dust formation in the space medium

Abstracts of 25 papers relating to condensation processes in the early solar system are presented. Special emphasis is given to the transition of an initial vapor phase in the space medium, the characterization of condensation environments, and condensation processes in the space medium. The question of whether some fraction of the solar system solids (particularly exemplified by meteoritic solids) may be interstellar grains that gathered in the region of the proto-sun, rather than being products of local condensation is addressed.

Robertson, P. C.↗
NASA NTRS1981

Crater populations on Ganymede and Callisto

Voyager 1 observations reveal heavily cratered surfaces on Ganymede and Callisto which suggest that a period of heavy bombardment occurred in the outer solar system. The overall crater density on Ganymede indicates that the oldest regions began recording the observed crater population at a later time than Callisto. A diameter-dependent loss of craters from 10-40 km occurs on Ganymede and may be due to ice formation or the formation of arcuate troughs. Evidence is given which suggests that the population of bodies responsible for the period of late heavy bombardment in the inner solar system is very different from that responsible for the late heavy bombardment in the outer solar system. In addition, it is postulated that Ganymede and Callisto may principally record a population of bodies that never penetrated the inner solar system in numbers great enough to leave a recognizable signature.

Strom, R. G.↗
NASA NTRS1992

Comet Yanaka (1988r) - A new class of carbon-poor comet

As part of a program to determine the chemical composition of a sample population of comets, a very unusual comet, Yanaka (1988r), was observed in January 1989. Although the comet showed the usual emissions of OI and NH2, it did not display any hint of C2 or CN emission. The comet is depleted in C2 by at least a factor of 100 and in CN by a factor of 25 relative to typical comets. If comets originate from interstellar clouds, Yanaka (1988r) could be an interloper from a cloud of different composition. If Yanaka (1988r) was formed within our solar system, the solar nebula was less uniform than assumed by most present models of formation.

Fink, Uwe↗
NASA NTRS1995

The mosaic structure of plasma bulk flows in the Earth's magnetotail

Moments of plasma distributions observed in the magnetotail vary with different time scales. In this paper we attempt to explain the observed variability on intermediate timescales of approximately 10-20 min that result from the simultaneous energization and spatial structuring of solar wind plasma in the distant magnetotail. These processes stimulate the formation of a system of spatially disjointed. highly accelerated filaments (beamlets) in the tail. We use the results from large-scale kinetic modeling of magnetotail formation from a plasma mantle source to calculate moments of ion distribution functions throughout the tail. Statistical restrictions related to the limited number of particles in our system naturally reduce the spatial resolution of our results, but we show that our model is valid on intermediate spatial scales Delta(x) x Delta(z) equal to approximately 1 R(sub E) x 1000 km. For these spatial scales the resulting pattern, which resembles a mosaic, appears to be quite variable. The complexity of the pattern is related to the spatial interference between beamlets accelerated at various locations within the distant tail which mirror in the strong near-Earth magnetic field. Global motion of the magnetotail results in the displacement of spacecraft with respect to this mosaic pattern and can produce variations in all of the moments (especially the x-component of the bulk velocity) on intermediate timescales. The results obtained enable us to view the magnetotail plasma as consisting of two different populations: a tailward-Earthward system of highly accelerated beamlets interfering with each other, and an energized quasithermal population which gradually builds as the Earth is approached. In the near-Earth tail, these populations merge into a hot quasi-isotropic ion population typical of the near-Earth plasma sheet. The transformation of plasma sheet boundary layer (PSBL) beam energy into central plasma sheet (CPS) quasi-thermal energy occurs in the absence of collisions or noise. This paper also clarifies the relationship between the global scale where an MHD description might be appropriate and the lower intermediate scales where MHD fails and large-scale kinetic theory should be used.

Ashour-Abdalla, M.↗
NASA NTRS1996

SOFIA: The Next Airborne Observatory

SOFIA (Stratospheric Observatory for Infrared Astronomy) will be a telescope with 2.5 m effective aperture operating at altitudes of 12.5 to 13.7 km in a Boeing 747 aircraft. It will enable astronomers on board to make observations which are impossible from the ground at wavelengths between 0.3 microns and 1.5 mm. Diffraction-limited imaging will be possible at wavelengths beyond about 10 microns. SOFIA's mobility will assure all-sky coverage and access to transient events from anywhere in the world. Some of the science topics to be studied will be star and planet formation, origin and evolution of biogenic materials, comets and planetary atmospheres in the solar system, the interstellar media of other galaxies, and phenomena at our galactic center. The SOFIA concept is based on 21 years of experience with NASA's Kuiper Airborne Observatory (KAO), which has been retired to help fund the project. As with the KAO, state-of-the-art focal plane instruments and a vigorous educational outreach program will be features of this new airborne astronomy facility. A more intensive flight program, approximately 150 flights per year, will accommodate many more guest investigators however. Planned as a collaboration between the United States and Germany, SOFIA is scheduled to begin a 20 year operating lifetime in 2001.

Erickson, E. F.↗
NASA NTRS2004

Identifying Organic Molecules in Space: The AstroBiology Explorer (ABE) Mission Concept

The AstroBiology Explorer (ABE) mission concept consists of a modest dedicated space observatory having a 60 cm class primary mirror cooled to T less than 50 K equipped with medium resolution cross-dispersed spectrometers having cooled large format near- and mid-infrared detector arrays. Such a system would be capable of addressing outstanding problems in Astrochemistry and Astrophysics that are particularly relevant to Astrobiology and addressable via astronomical observation. The mission's observaticxiai program woiild make fundamental scieztific: prngress in establishing the nature, distribution, formation and evolution of organic and other molecular materials in the following extra-terrestrial environments: 1) The Outflow of Dying Stars; 2) The Diffuse Interstellar Medium (DISM); 3) Dense Molecular Clouds, Star Formation Regions, and Young Stellar/Planetary Systems; 4) Planets, Satellites, and Small Bodies within the Solar System; and 5) The Interstellar Media of Other Galaxies ABE could make fundamental progress in all of these area by conducting a 1 to 2 year mission to obtain a coordinated set of infrared spectroscopic observations over the 2.5 - 20 micron spectral range at a spectral resolution of R greater than 2500 of about 1500 galaxies, stars, planetary nebulae, young stellar objects, and solar system objects.

Ennico, Kimberly↗
NASA NTRS2004

Chondrites and the Protoplanetary Disk, Part 4

Topics discussed include: Cosmochemical fractionations, Chondritic meteorites and their components, Jet flows: Formation and thermal processing of solids in protoplanetary disks, A Search for Solar-System processing signatures in presolar grains, Experimental study of iron metal condensation, The chondrite types and their origins, Spinel-rich spherules from murchison, etc.

Source record↗
NASA NTRS2004

Identifying Organic Molecules in Space: The AstroBiology Explorer (ABE) Mission Concept

The AstroBiology Explorer (ABE) mission concept consists of a dedicated space observatory having a 60 cm class primary mirror cooled to T < 50 K equipped with medium resolution cross-dispersed spectrometers having cooled large format near- and mid-infrared detector arrays. Such a system would be capable of addressing outstanding problems in Astrochemistry and Astrophysics that are particularly relevant to Astrobiology and addressable via astronomical observation. The mission s observational program would make fundamental scientific progress in establishing the nature, distribution, formation and evolution of organic and other molecular materials in the following extra-terrestrial environments: 1) The Outflow of Dying Stars, 2) The Diffuse Interstellar Medium, 3) Dense Molecular Clouds, Star Formation Regions, and Young StellarPlanetary Systems, 4) Planets, Satellites, and Small Bodies within the Solar System, and 5 ) The Interstellar Media of Other Galaxies. ABE could make fundamental progress in all of these areas by conducting a 1 to 2 year mission to obtain a coordinated set of infrared spectroscopic observations over the 2.5-20 micron spectral range at a spectral resolution of R > 2000 of about 1500 objects including galaxies, stars, planetary nebulae, young stellar objects, and solar system objects. Keywords: Astrobiology, infrared, Explorers, interstellar organics, telescope, spectrometer, space, infrared detectors

Ennico, K. A.↗
NASA NTRS2022

The First Returned Samples From A C-Type Asteroid Show Kinship to the Chemically Most Primitive Meteorites

Bulk chemical and isotopic compositions, and mineralogy in the asteroid (162173) Ryugu samples show that Ryugu is mainly composed of materials related to the CI (Ivuna-like) carbonaceous chondrite group. The samples consist predominantly of minerals produced by aqueous alteration in a parent planetesimal from which Ryugu was derived. The 53Mn-53Cr systematics of dolomite suggest that this alteration occurred 5.2 (+0.7/–0.8) million years after formation of Ca-Al-rich inclusions, the first solids formed in the Solar System. The aqueous alteration temperature at the time dolomite and magnetite coprecipitated was 37±10°C. Unlike in CI chondrites, phyllosilicates in Ryugu have lost most of their interlayer water, but retained structural water. This indicates that following aqueous alteration the Ryugu samples avoided heating above ~90°C.

Tetsuya Yokoyama↗
NASA NTRS1993

Variety in planetary systems

Observation of circumstellar disks, regular satellite systems of outer planets, and planet-size objects orbiting pulsars support the supposition that formation of planetary systems is a robust, rather than a fragile, byproduct of the formation and evolution of stars. The extent to which these systems may be expected to resemble one another and our Solar System, either in overall structure or in detail remains uncertain. When the full range of possible stellar masses, disk masses, and initial specific angular momenta are considered, the possible variety of planetary configurations is very large. Numerical modeling indicates a difference between the formation of small, inner, terrestrial planets and the outer planets.

Wetherill, George W.↗
NASA NTRS1991

Clathrate type 2 hydrate formation in vacuo under astrophysical conditions

The properties of clathrate hydrates were used to explain the complex and poorly understood physical processes taking place within cometary nuclei and other icy solar system bodies. Most of all the experiments previously conducted used starting compositions which would yield clathrate types I hydrates. The main criterion for type I vs. type II clathrate hydrate formation is the size of the guest molecule. The stoichiometry of the two structure types is also quite different. In addition, the larger molecules which would form type II clathrate hydrates typically have lower vapor pressures. The result of these considerations is that at temperatures where we identified clathrate formation (120-130 K), it is more likely that type II clathrate hydrates will form. We also formed clathrate II hydrates of methanol by direct vapor deposition in the temperature range 125-135 K.

Blake, D. F.↗
NASA NTRS1989

The early solar system abundance of Pu-244 as inferred from the St. Severin chondrite

The isotopic composition of Xe released in stepwise heating of neutron-irradiated samples of the St. Severin chondrite was measured. This analysis shows that at the time of formation of most chondritic meteorites, approximately 4.56 x 10 to the 9th yr ago, the atomic ratio of Pu-244/U-238 was 0.0068 + or - 0.0010 in chondritic meteorites. This value is believed to be more reliable that inferred from earlier analyses of St. Severin and is the best estimate for the early solar system abundance of Pu-244. The comparison of Xe compositions between irradiated and unirradiated samples shows that the composition of trapped (ambient) Xe in St. Severin has a significantly lower value of Xe-136/Xe-130 than average carbonaceous chondrites.

Hudson, G. B.↗
NASA NTRS2015

New Horizons Successful Completes the Historic First Flyby of Pluto and Its Moons

On July 14, 2015, after a 9.5 year trek across the solar system, NASA's New Horizons spacecraft flew by the dwarf planet Pluto and its system of moons, taking imagery, spectra and in-situ particle data. Data from New Horizons will address numerous outstanding questions on the geology and composition of Pluto and Charon, plus measurements of Pluto's atmosphere, and provide revised understanding of the formation and evolution of Pluto and Charon and its smaller moons. This data set is an invaluable glimpse into the outer Third Zone of the solar system. Data from the intense July 14th fly-by sequence will be downlinked to Earth over a period of 16 months, the duration set by the large data set (over 60 GBits) and the limited transmitted bandwidth rates (approx. 1-2 kbps) and sharing the three 70 m DSN assets with our missions. The small fraction (approx. 1%) of data downlinked during the early phase of the flyby has already revealed Pluto and Charon to be very different worlds, with increasing and dynamic complexity.

Pluto↗