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All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Dynamics of planetary atmospheres

The overall goal is to illuminate the mechanisms that control weather and climate on the Earth and other planets. Each planet presents its own puzzling behavior - the stability of jets and vortices in Jupiter's otherwise turbulent atmosphere, the superrotation of the Venus atmosphere, the interplay of dust, polar volatiles, and climate change in Mars, the supersonic meteorology of Io, and the counterintuitive equator-to-pole temperature gradients on the outer planets. The data sets are generally those obtained from spacecraft - cloud-tracked winds, radiometrically inferred temperatures, and the results of in situ observations where appropriate. The approach includes both data analysis and modeling, ranging from analytic modeling to time-dependent numerical modeling of atmospheric dynamics. The latter approach involves the use of supercomputers such as the San Diego Cray. Progress is generally made when a model with a small number of free parameters either fits a data set that has a large number of independent observations or applies to several planets at once.

Ingersoll, Andrew P.↗
NASA NTRS1974

Geodetic and dynamical properties of planets

Data concerning planetary dynamics and geodesy are severely limited because, at present, only one planetary system in the universe can be studied. It is, therefore, impossible to base the study of planets on a significant statistical sample. The gravity fields of the planets are discussed, giving attention to the various space missions involved in the collection of the relevant data. Other subjects considered include planetary shape and topography, planetary rotations, and planetary interiors. The basic problem in finding an acceptable model for the planetary interior is to specify the chemical composition with depth and then to find a physically realistic equation for the material.

Anderson, J. D.↗
NASA NTRS1984

Unsolved problems in planetary ring dynamics

Voyager photographic data are used for microscopic and macroscopic analyses of the dynamics of the Saturn rings. Attention is given to particle collisions, local velocity dispersion, the particle size distribution, mechanisms governing the ring structure and interactive effects with Saturn satellite orbits. The mechanical properties and collision dynamics of the particles are discussed, along with models for perturbed and unperturbed disks. The forces involved and true scale of particle erosion are considered, as are instabilities in the rings, satellite torques, resonances, and the time scale for the evolution of the satellite orbits. Finally, the possibility that angular momentum exchanges are occurring between individual rings and satellite orbits is examined.

Borderies, N.↗
NASA NTRS1987

Planetary ring dynamics and morphology

Evidence for a moonlet belt in the region between Saturn's close-in moonrings Pandora and Prometheus is discussed. It is argued that little-known observations of magnetospheric electron density by Pioneer 11 imply substantial, ongoing injections of mass into the 2000 km region which surrounds the F ring. A hypothesis is presented that these events result naturally from interparticle collisions between the smaller members of an optically thin belt of moonlets. Also discussed is work on Uranus ring structure and photometry, image processing and analysis of the Jonian ring strucure, photometric and structural studies of the A ring of Saturn, and improvements to an image processing system for ring studies.

Cuzzi, Jeffrey N.↗
NASA NTRS1991

Numerical exploration of planetary arc dynamics

After analytically characterizing the response of a test particle to the combined effects of corotation and Lindblad resonances, due to the satellites of Neptune, as two coupled dynamical systems whose coupling depends on the collective effects in the arc, a formula is obtained for the energy imparted by the Lindblad resonance. This energy confines the arc material around the corotation resonance radius. The fact that the gradient of the torque density around the arc must be negative confirms the constraints defined by Lin et al. (1987) on the relative positions of the corotation and the Lindblad resonances if the arc is to be stable. These results are tested with a direct numerical simulation for two different arc configurations.

Sicardy, Bruno↗
NASA NTRS2002

Dynamics of Planetary Atmospheres

The PI had nineteen papers either published or in press in 1999 through early 2002. Ten of these (Thomas et al. 1999, Geisler et al. 1999, Vasavada et al. 1999, Little et al. t999, Gierasch et al. 2000, Ingersoll et al. 2000, Thomas et al. 2000, Dyudina et al. 2001, Chang et al. 2001, Wang and Ingersoll 2002) were largely supported by the Mars Global Surveyor project and the Galileo project. The other nine papers were largely supported under this grant, and are listed in boldface below. Six of the nine are research papers. Their titles and abstracts are reproduced below. The New Solar System chapter and the Meteorology at the Millennium chapter are review articles, and the World Book Encyclopedia chapter is a popular article. Their title pages and abstracts are also reproduced below.

Ingersoll, Andrew P.↗
NASA NTRS2004

Lunar and Planetary Surface Dynamics and Early History

The research described by this annual research report covers the following subjects: A) Early solar system processes and time scales using I-Xe chronometry; B) I-Xe studies of individual chondrules; C) Additional Ongoing Projects.

Hohenberg, Charles M.↗
NASA NTRS2015

The Role of the Hall Effect in Global Structure and Dynamics of Planetary Magnetospheres: Ganymede as a Case Study

We present high-resolution Hall MHD simulations of Ganymede's magnetosphere demonstrating that Hall electric fields in ion-scale magnetic reconnection layers have significant global effects not captured in resistive MHD simulations. Consistent with local kinetic simulations of magnetic reconnection, our global simulations show the development of intense field-aligned currents along the magnetic separatrices. These currents extend all the way down to the moon's surface, where they may contribute to Ganymede's aurora. Within the magnetopause and magnetotail current sheets, Hall J x B forces accelerate ions to the local Alfven speed in the out-of-plane direction, producing a global system of ion drift belts that circulates Jovian magnetospheric plasma throughout Ganymede's magnetosphere. We discuss some observable consequences of these Hall-induced currents and ion drifts: the appearance of a sub-Jovian 'double magnetopause' structure, an Alfvenic ion jet extending across the upstream magnetopause, and an asymmetric pattern of magnetopause Kelvin-Helmholtz waves.

Magnetic Reconnection↗
NASA NTRS1974

Geodetic and dynamical properties of planets

The study of planetary dynamics and geodesy is a difficult subject. This is so, not simply because of the complexity of the interactions between several scientific disciplines, including geophysics, geology, geochemistry, seismology, celestial mechanics, radar astronomy, and meteoritics, but perhaps more fundamentally, because of a lack of data. Although it is true that the space age has brought about important new observational techniques, which are responsible in large part for the rapid developments in planetary science over the past decade, and although we should expect to see significant progress in the field over the next few years, it is still a sad fact that data will be severely limited for an indefinite period of time in the future. The basic problem is that we can observe and study, at present, only one planetary system in the universe. This system, our solar system, contains only four major planets, five terrestrial planets, where we are inclined to include the moon but exclude Pluto, and a fairly limited collection of debris, presumably left over from some inadequately understood formation process. Thus it is impossible to base the study of planets on a significant statistical sample.

J. D.. Anderson↗
NASA NTRSDate not supplied

Can Tracked Great Frigatebirds (Fregata minor) be Used to Measure the Dynamics of the Planetary Boundary Layer Height?

Observing the dynamics of the planetary boundary layer (PBL) will require creative combinations of space-based and in-situ measurements. Animals fitted with biologgers have been used to gather data and parameterize physical models in various settings and may be a useful addition to the suite of space-based measurements that NASA is considering. For example, great frigatebirds (Fregata minor) generally fly below 700m but have been shown to routinely climb up to 2,000 meters during the day, occasionally reaching heights over 4,000 meters. This suggests that they may be tracking boundary layer height dynamics as they soar and glide on air currents with little energetic cost. We show here that the high-altitude climbing heights of great frigatebirds carrying GPS/accelerometer biologgers (e-obs GmbH Bird Solar 15g) at Palmrya Atoll, Pacific Ocean, are consistent with the long-term climatology (2006-2019) of the local planetary boundary layer height, and that these soaring heights can be reliably extracted from the tag data. Additional study is needed to determine how well movement data from tracked birds can constrain PBL height, but this work demonstrates the potential for animal-borne sensors to complement space-based measurements. Biologging data were contributed by the USGS and the Nature Conservancy's Palmyra Bluewater Research (PBR) study and analyzed as part of NASA’s Internet of Animals project.

Planetary Boundary Layer Height↗
NASA NTRS1993

The planetary nebula system and dynamics of NGC 5128. I - Planetary nebulae as standard candles

We present the result of a planetary nebula (PN) survey of the nearby giant elliptical galaxy NGC 5128 performed with CCD cameras at the prime focus of the CTIO 4 m telescope. By comparing CCD images centered on the characteristic emission line forbidden O III 5007 A and on the adjacent continuum, we identify a total of 785 PNs in areas extending 20 kpc along the photometric major axis and covering the whole galaxy to 10 kpc. From these data, we form a complete sample of 224 PNs extending to a dereddened limiting magnitude of m5007 = 24.8, which extends 1.5 mag down the PN luminosity function (PNLF). Adopting a foreground extinction of E(B-V) = 0.1, we derive a distance to the galaxy of 3.5 +/- 0.2 Mpc, in excellent agreement with the surface brightness fluctuation method. No population effect on the bright cutoff of PNLF is observed in the isophotal radius range of 2-16 kpc, but the luminosity specific PN density seems to increase with radius inside of 7 kpc, in agreement with the alpha(2.5)-color relation observed for other galaxies.

Hui, Xiaohui↗
NASA NTRS1984

Planetary rings - A dynamic, evolving subject

Attention is drawn to current attempts to present the results of theoretical dynamical studies of the planetary rings, and to propagate observational results on ring structure and physical properties that are relevant to dynamical interpretations. Like earlier, optical models, dynamical models tend to assume simplified, single sized, smooth, and round, ring-constituting particles; a tendency is noted which confuses particles dominating optical properties with those that dominate dynamics.

Greenberg, R.↗
NASA NTRS1984

Dynamics of early planetary gear trains

A method to analyze the static and dynamic loads in a planetary gear train was developed. A variable-variable mesh stiffness (VVMS) model was used to simulate the external and internal spur gear mesh behavior, and an equivalent conventional gear train concept was adapted for the dynamic studies. The analysis can be applied either involute or noninvolute spur gearing. By utilizing the equivalent gear train concept, the developed method may be extended for use for all types of epicyclic gearing. The method is incorporated into a computer program so that the static and dynamic behavior of individual components can be examined. Items considered in the analysis are: (1) static and dynamic load sharing among the planets; (2) floating or fixed Sun gear; (3) actual tooth geometry, including errors and modifications; (4) positioning errors of the planet gears; (5) torque variations due to noninvolute gear action. A mathematical model comprised of power source, load, and planetary transmission is used to determine the instantaneous loads to which the components are subjected. It considers fluctuating output torque, elastic behavior in the system, and loss of contact between gear teeth. The dynamic model has nine degrees of freedom resulting in a set of simultaneous second order differential equations with time varying coefficients, which are solved numerically. The computer program was used to determine the effect of manufacturing errors, damping and component stiffness, and transmitted load on dynamic behavior. It is indicated that this methodology offers the designer/analyst a comprehensive tool with which planetary drives may be quickly and effectively evaluated.

August, R.↗