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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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NASA NTRS2022

Evolution of X-Ray Activity in <25 Myr Old Pre-main Sequence Stars

Measuring the evolution of X-ray emission from pre-main-sequence (PMS) stars gives insight into two issues: the response of magnetic dynamo processes to changes in the interior structure, and the effects of high-energy radiation on protoplanetary disks and primordial planetary atmospheres. We present a sample of 6003 stars with ages 7–25 Myr in 10 nearby open clusters from Chandra X-ray and Gaia-EDR3 surveys. Combined with previous results in large samples of younger (≲5 Myr) stars in MYStIX and SFiNCs star-forming regions, mass-stratified activity-age relations are derived for the early phases of stellar evolution. X-ray luminosity (LX) is constant during the first few Myr, possibly due to the presence of extended X-ray coronas insensitive to temporal changes in stellar size. LX then decays during the 7–25 Myr period, more rapidly as stellar mass increases. This decay is interpreted as decreasing efficiency of the α2 dynamo as radiative cores grow and a solar-type αΩ dynamo emerges. For more massive 3.5–7 M⊙ fully radiative stars, the X-ray emission plummets—indicating the lack of an effective magnetic dynamo. The findings provide improved measurements of high-energy radiation effects on circumstellar material, first for the protoplanetary disk and then for the atmospheres of young planets. The observed X-ray luminosities can be so high that an inner Earth-mass rocky, unmagnetized planet around a solar-mass PMS star might lose its primary and secondary atmospheres within a few (several) million years. PMS X-ray emission may thus have a significant impact on the evolution of early-planetary atmospheres and the conditions promoting the rise of habitability.

Konstantin V Getman↗

NASA NTRS1992

The meteoritic contribution to dust and aerosols in the atmosphere of Mars

The continuous, planet-wide accretion of meteoritic material onto the Earth and Moon has been established by stratospheric sampling on Earth and chemical abundance analysis of the lunar soils. Meteoritic material must contribute in a similar manner to the atmospheres of all the planets and moons of the inner solar system. Although meteorites that survive planetary entry unmelted are the primary contributors, secondary contributions come from: (1) recondensed vapor in meteorite trails; and (2) fragmentation debris from low density meteoroids. These three contributions provide a constant planet-wide source of atmospheric particulates on Mars. In the size range greater than 1 micro-m in diameter micrometeorites which survive atmospheric entry unmelted are the major contributor, accounting for about 8.6 x 10(exp 6) kg/year of material. For particles less than 1 micro-m in diameter the majority of the mass is likely to come from recondensed meteoric vapor, which could account for approx. 2 x 10(exp 6) kg/year.

Flynn, G. J.↗

NASA NTRS1977

Discovering Jupiter. II

Data derived from Pioneer 10 and Pioneer 11 and other sources on the Jovian magnetosphere, the circum-Jovian radiation belts, and Jupiter's radio emission are presented at some length, descriptions are given of the principal Jovian satellites (Io, Europa, Ganymede, Callisto), and inferences are drawn on the origin of the planet and its place in the solar system. The inner, middle, and outer regions of the magnetosphere, the bow shock wave, and the particularly heavy intensity of the inner radiation belt region (within 1.44 million km of the planet) are discussed. All of the major satellites except Callisto lie immersed in the intense radiation belts. Jupiter's failure to become a stellar companion to the sun, Io's action in 'switching on' Jovian radio emission, and other Pioneer discoveries relating to asteroids, the solar system in general, and trans-Jovian space, are discussed

Source record↗

NASA NTRS1998

The Dependence of Signal-To-Noise Ratio (S/N) Between Star Brightness and Background on the Filter Used in Images Taken by the Vulcan Photometric Planet Search Camera

The Vulcan Photometric Planet Search is the ground-based counterpart of Kepler Mission Proposal. The Kepler Proposal calls for the launch of telescope to look intently at a small patch of sky for four year. The mission is designed to look for extra-solar planets that transit sun-like stars. The Kepler Mission should be able to detect Earth-size planets. This goal requires an instrument and software capable of detecting photometric changes of several parts per hundred thousand in the flux of a star. The goal also requires the continuous monitoring of about a hundred thousand stars. The Kepler Mission is a NASA Discovery Class proposal similar in cost to the Lunar Prospector. The Vulcan Search is also a NASA project but based at Lick Observatory. A small wide-field telescope monitors various star fields successively during the year. Dozens of images, each containing tens of thousands of stars, are taken any night that weather permits. The images are then monitored for photometric changes of the order of one part in a thousand. These changes would reveal the transit of an inner-orbit Jupiter-size planet similar to those discovered recently in spectroscopic searches. In order to achieve a one part in one thousand photometric precision even the choice of a filter used in taking an exposure can be critical. The ultimate purpose of an filter is to increase the signal-to-noise ratio (S/N) of one's observation. Ideally, filters reduce the sky glow cause by street lights and, thereby, make the star images more distinct. The higher the S/N, the higher is the chance to observe a transit signal that indicates the presence of a new planet. It is, therefore, important to select the filter that maximizes the S/N.

Mena-Werth, Jose↗

NASA NTRS1974

Pioneer Venus probe design

The summary provides descriptions for a set of probes designed to explore an inner rather than an outer planet, and designed to survive to 100 bars rather than 10 bars. The probes carry a variety of scientific instruments and their supporting integrated subsystems are adjusted to Venus environmental conditions.

Nolte, L. J.↗

NASA NTRS1978

Abundances of isotopes in planetary atmospheres

Carbon and oxygen isotopes show no large anomalies on Venus (no more than 10-15%) or Mars (less than 5%); the high value of N-15/N-14 found on Mars is explained by nonthermal escape of nitrogen. The isotopes of nonradiogenic noble gases in the atmosphere of Mars exhibit abundance patterns similar to those in the primordial component of meteoritic gases and in the earth's atmosphere. This implies that gas fractionation took place in the inner solar nebula prior to planet formation. The relatively high value of Xe-129 on Mars emphasizes its deficiency on earth, implying a difference in accretion histories of volatiles for the two planets. In the outer solar system, normal isotope ratios for nitrogen and carbon on Jupiter, and for carbon on Saturn are found, but precision is low (+ or - 15% at best). Controversy exists about the correct value of D/H, with current estimates ranging from 2.3 plus or minus 1.1 to 5.1 plus or - 0.7 times 10 to the minus 5th. Planetary missions planned for the next few years should add considerably to the quantity and quality of these data.

Owen, T.↗

NASA NTRS1982

The moons of Saturn

Knowledge gained of the 17 Saturn moons with observations by the Voyager spacecraft are reviewed. Titan was found to have the only atmosphere, which is opaque and precludes geologic inferences. Synchronous rotation is experienced by the 14 inner moons, with a constant inner face turned toward the planet. Phoebe is too far away from the planet to lose its spin to planetary tidal forces, and has an orbit inclined 150 deg from the equatorial plane, while Iapetus is inclined 14.7 deg in its orbit. The abundance of ice on the moons is accepted as evidence of condensation formation of the moons at very low temperatures. Newly discovered moons of Saturn, including both the shepherd moons, which are suspected to maintain the rings in place, and the moons discovered by earth-based astronomy, are discussed. Finally, photographs of all the moons are examined for definitive details.

Soderblom, L. A.↗

NASA NTRS1984

The planet crossing asteroid survey: Progress in the analysis of populations and terrestrial-planet cratering rates

The Planet-Crossing Asteroid Survey (PCAS) is making steady progress toward the accumulation of the data required to make improved estimates of the populations and cratering rates which can be compared with the existing record of impact events. The PCAS is the chief source of new objects on which to base these calculations over the past decade, and is an integral part of the continuing refinement of the estimates used in planetological applications. An adjunct effort to determine albedo statistics from photometry of UCAS plates is being pursued as well, to better define the magnitude frequency distributions of asteroids. This will improve the quality of the population and collision probability calculations. The survey effort continues to discover new asteroids whose orbital characteristics may reveal the origin and evolution mechanisms reponsible for the transport of the planet-crossing asteroids to the inner solar system.

Helin, E. F.↗

NASA NTRS1988

The cratering record on Mercury and the origin of impacting objects

The cratering records of terrestrial planets are discussed with special consideration given to Mercury. The geologic units on Mercury most relevant to its cratering record are reviewed, and new observations are presented on the issues of equilibrium and saturation. The implications of the Mercurian cratering record for geologic processes are examined. Particular attention is given to the origin of objects responsible for the period of late heavy bombardment on terrestrial planets; it is suggested that the impactors were accretional remnants left over from the formation of the terrestrial planets and confined to the inner solar system. The cratering record in the outer solar system may have been produced largely by objects in planetocentric orbits.

Strom, Robert G.↗

NASA NTRS1991

Palomar Planet-Crossing Asteroid Survey (PCAS)

The objective is the discovery and follow-up of planet-crossing asteroids, related inner-belt asteroids, and comets. The primary program is carried out with the 0.46 m Schmidt telescope at Palomar Observatory. The results, subsequent observations, and analysis provide insight into their populations, orbits, origins, physical characteristics (composition, size, and shape), potential for impact, relationships to comets and meteorites, and for future spacecraft mission candidates.

Helin, Eleanor F.↗

NASA NTRS2014

Timing of Formation of a Wassonite-bearing Chondrule

Wassonite, ideally stoichiometric TiS, is a titanium monosulfide recently discovered in the Yamato 691 EH3 enstatite chondrite. Wassonite grains were located within the mesostasis of a single barred olivine chondrule. Such chondrules likely formed in the solar nebula by melting of fine grained precursor dust. The reduced nature of enstatite chondrites, and the wassonite-bearing chondrule in particular, may suggest precursor materials included Ti-bearing troilite, metallic Fe-Ni, and possibly graphite. Under the reducing conditions present in enstatite chondrites S can partition more readily into silicate melt, leading to raised Ti content of the residual Fe-FeS melt. By the time sulfide crystallized from the melt, the Ti concentration was high enough to form small grains of pure TiS - wassonite. As a mineral not previously observed in nature wassonite and its host chondrule may provide additional constraints on physical and chemical conditions in the solar nebula at a specific time and location relevant to planetary formation. Enstatite chondrites and Earth share similar isotopic compositions of Cr, Ni, Ti, O and N. Understanding the formation conditions of enstatite chondrite chondrules may therefore have wider relevance for terrestrial planet accretion and other early inner solar system processes. Here we present preliminary results of an investigation of the Al-Mg systematics of the only known wassonite-bearing chondrule. The goal of this study is to determine whether this chondrule's formation was contemporaneous with other enstatite chondrite chondrules and to establish its place in the broader timeline of solar system events.

Needham, A. W.↗

NASA NTRS2018

Hydrovolcanic Astromaterials in the Lab

Zag and Monahans (1998) are H chondrite regolith breccias that contain 4.5 GY old halite crystals which in turn contain abundant inclusions of aqueous fluids, solids and organics. We have previously proposed that these halites originated on a hydrovolcanically-active C class asteroid, probably Ceres, or a trans-neptunian object (TNO - or P- or D-class asteroid) injected into the inner solar system during giant planet migration. We have begun a detailed analysis of organics and other solids trapped within the halite, which we hypothesize sample the mantle of the halite parent object, and are examining a halite-bearing C1 chondrite clast also found in Zag, which is similar to the solids in the halite. These investigations will reveal the water-rock interactions on the hydrovolcanically-active parent world.

Zolensky, M. E.↗

NASA NTRS1977

Observations of Uranus occultation events

An analysis of photometric data obtained during the Uranus appulse to SAO 158687 shows three occultation events which appear to coincide with portions of the Uranian ring system. Two occultation events were associated with the alpha ring and one with the beta ring of the planet; the alpha ring event suggests a ring model with a random distribution of occulting bodies of about 1 km diameter, and an areal density of about 50% over a band 10 km wide. Calculations indicate that neither the inner nor outer rings of the planet are truly concentric circles (to within their radius). In addition, determination of the ring centers can be used to locate the center of mass of the planet, and an upper limit of 26,300 km can be assigned to its radius.

Hubbard, W. B.↗

NASA NTRS2021

The Asymmetric Inner Disk of the Herbig Ae Star HD 163296 in the Eyes of VLTI/MATISSE: Evidence for a Vortex?

Context.A complex environment exists in the inner few astronomical units of planet-forming disks. High-angular-resolution observa-tions play a key role in our understanding of the disk structure and the dynamical processes at work.Aims.In this study we aim to characterize the mid-infrared brightness distribution of the inner disk of the young intermediate-massstar HD 163296 from early VLTI/MATISSE observations taken in theL- andN-bands. We put special emphasis on the detection ofpotential disk asymmetries.Methods.We use simple geometric models to fit the interferometric visibilities and closure phases. Our models include a smoothedring, a flat disk with an inner cavity, and a 2D Gaussian. The models can account for disk inclination and for azimuthal asymmetriesas well. We also perform numerical hydrodynamical simulations of the inner edge of the disk.Results.Our modeling reveals a significant brightness asymmetry in theL-band disk emission. The brightness maximum of the asym-metry is located at the NW part of the disk image, nearly at the position angle of the semimajor axis. The surface brightness ratio inthe azimuthal variation is3.5±0.2. Comparing our result on the location of the asymmetry with other interferometric measurements,we confirm that the morphology of ther<0.3au disk region is time-variable. We propose that this asymmetric structure, located in ornear the inner rim of the dusty disk, orbits the star. To find the physical origin of the asymmetry, we tested a hypothesis where a vortexis created by Rossby wave instability, and we find that a unique large-scale vortex may be compatible with our data. The half-lightradius of theL-band-emitting region is0.33±0.01au, the inclination is52◦+5◦−7◦, and the position angle is143◦±3◦. Our models predictthat a non-negligible fraction of theL-band disk emission originates inside the dust sublimation radius forμm-sized grains. Refractorygrains or large (&10μm-sized) grains could be the origin of this emission.N-band observations may also support a lack of smallsilicate grains in the innermost disk (r.0.6au), in agreement with our findings fromL-band data.

J Varga↗

NASA NTRS1992

Energetic particle signatures of satellites and rings in Neptune's magnetosphere

The cosmic ray system on Voyager 2 found a trapped radiation environment in Neptune's inner magnetosphere which is controlled primarily by absorption at the rings and satellite surfaces. The intensity of electrons with kinetic energies approximately greater than 1 MeV shows particularly strong and narrow signatures associated with absorption by the satellite 1989N1 at an orbital radius of 4.75 Neptune radii. Closer to the planet are several signatures of the inner satellites and rings. Absorption limits the intensity of the inner radiation belt sufficiently for the maximum intensity to occur outside the orbit of 1989N1 at a magnetic L shell of about 7. Radial profiles of the electron phase space density show that electrons diffuse inward from a source in the outer magnetosphere. Many of the inward-diffusing electrons are absorbed upon reaching a satellite orbital radius, but the finite absorption efficiency allows some of the electrons to pass by unaffected. The locations of the satellite and ring signatures also provide constraints on the nondipolar components of the planetary magnetic field.

Selesnick, R. S.↗

NASA NTRS2016

High-Contrast Imaging of Epsilon Eridani with Ground-Based Instruments

Epsilon Eridani is one of the nearest solar-type stars. Its proximity and relatively young age allow high-contrast imaging observations to achieve sensitivities to planets at narrow separations down to an inner radius of approximately 5 AU. Previous observational studies of the system report a dust disk with asymmetric morphology as well as a giant planet with large orbital eccentricity, which may require another massive companion to induce the peculiar morphology and to enhance the large orbital eccentricity. In this paper, we report results from deep high-contrast imaging observations to detect the previously reported planet and search for other unseen less massive companions with Subaru/HiCIAO, Gemini-South/NICI, and VLT/NACO. No positive detection was made, but high-contrast measurements with the CH4S narrow-band filter of HiCIAO achieved sensitivities at 14.7 mag differential magnitude level, at an angular separation of 1.0''. In terms of planetary mass, as determined by cooling evolutionary models, the highest sensitivities were achieved by the Lp broad-band filter of NACO, resulting in sensitivities corresponding to 1.8, 2.8, and 4.5 M(sub jup) at the projected separation of 3 AU, if 200, 400, and 800 Myr is assumed for the age of the system, respectively. We also discuss origins of the dust disk from the detection sensitivity in the planetary mass and find that a less massive eccentric planet is preferred for disk stirring, which is consistent with the orbital parameters of epsilon Eri b claimed from the previous long-term radial velocity monitoring.

Epsilon Eridani↗

NASA NTRS1998

Lasers in Earth and Planetary Exploration

For over 3 decades, lasers have been a tool of the space programs of the world for accomplishing a variety of engineering and scientific objectives. The majority of these uses have, however, been largely Earth-based and only a few lasers have actually been flown and operated in Earth orbit and even fewer on missions to the planets. However, in the last few years laser altimeters, lidars, and ranging systems have been part of space missions to the moon, an asteroid, and Mars; and more are planned and contemplated in the future exploration of the Earth and solar system. Early in 1994, the Clementine mission was launched to the moon and carried a laser altimeter that made the first systematic topographic survey of the moon during its 2-month observation period. This mission significantly improved our understanding of the shape and topography of the moon and along with gravity information obtained from the tracking data modified some of our thinking about the moon, the thickness of ice crust and the isostatic state of the highlands and basins. On September 11, 1997, the Mars Global Surveyor (MGS) entered into orbit around Mars and the Mars Orbiter Laser Altimeter (MOLA) started to map the topography of the planet to unprecedented accuracy. On its first pass across the planet, MOLA showed large areas of the northern hemisphere to be flatter than any other known surface on Earth or any other body explored to date. In January 1999, the NEAR spacecraft which carries a laser ranger (NLR), will arrive at the S-type asteroid, Eros, and during the following year the NLR will help determine the shape and rotational dynamics of this asteroid. In the Spring of 2000, the Vegetation Canopy Lidar (VCL) mission will be launched and employing a multi-beam laser altimeter (MBLA) will measure the Earth's tree canopy shapes and heights and begin to globally monitor the biomass. The following year, in 2001, the Geoscience Laser Altimeter System, which carries a 2 wavelength laser altimeter of a few centimeter accuracy, will begin a multi-year observation program of the Earth's icecaps, land mass, oceans and the clouds of the atmosphere. At the same time, laser ranging to satellites and the moon is likely to be poised to reach to the planets and track spacecraft throughout the inner solar system by applying optical transponder technology to increase its distance capability.

Smith, David E.↗

NASA NTRS1998

The Dynamical Evolution of the Earth-Moon Progenitors: Results and Interpretation - 2

Substantial evidence indicates that the Earth-Moon system formed about 100 m.y. after the oldest meteorites and that the inner solar system had five terrestrial planets for several tens of millions of years before the hypothesized Moon-forming impact. We present and discuss some results from a series of N-body integrations in which the mass ratio of the Earth-Moon progenitors is 8:1 or 1:1. We want to know if it is plausible to have the Earth-Moon progenitors collide between 8 m.y. and 200 m.y. after the other planets had formed and to have the resulting system look "similar" to the solar system. If a collision occurs, the integrations tell us which two bodies collide and the time of the collision. We also determine the angular momentum deficit (AMD) of the resulting terrestrial planets. Additionally, we calculate several parameters of the collision. We use the AMD of the terrestrial planets to compare the resulting system to our own. The AMD or a planet is the difference between its orbital angular momentum and its orbital angular momentum if it were in a circular orbit with zero inclination.

Rivera, E.↗