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NASA NTRS2024

Structural Differences Between Insoluble Organic Matter in Matrix and Chondrules: Potential Insights into Pre-Parent Body Thermal Alteration

Carbon is a major molecular constituent of primitive chondrites of low petrologic grade. A majority of the carbon (>70%) is in the insoluble organic matter (IOM) fraction that cannot be extracted from the meteorite sample using polar or nonpolar solvents. The IOM is comprised of a kerogen-like macromolecular carbon (MMC) structure that consists of aromatic rings connected by highly branching aliphatic chains. Raman spectroscopy is highly sensitive to IOM due to a strong resonance enhancement that occurs for all visible excitation wavelengths, making Raman a powerful in-situ probe of IOM. The Raman spectrum of IOM consists of two primary bands, the G band originates from all carbon-carbon bonds in the MMC structure and the D band that originates from carbon 6-member ring breathing motions. The peak position and width of the G and D bands probe the structure of the IOM. Using Raman spectroscopy, the IOM structure has been shown to correlate with the thermal alteration history of the meteorite, allowing for petrologic grade classification to the tenths place in the 3.0-3.9 range. Here, we have collected Raman images of GRA 06100,41 (CR2) for the examination of the IOM spatial distribution and observe significant differences between the IOM in the matrix and chondrules.

R S Jakubek↗

NASA NTRS1980

A simulation study of cold electron heating by loss cone instabilities

Results are presented of a computer simulation study of electron cyclotron harmonic waves; an electrostatic finite size particle simulation code is used. The initial electron velocity distribution function is modeled as a hot ring perpendicular to the ambient magnetic field and a cold Maxwellian component. Nonlinear cyclotron resonance is found to be the saturation mechanism of the unstable waves and the heating mechanism of the cold electrons. The results can be related to certain ionospheric phenomena.

Ashour-Abdalla, M.↗

NASA NTRS1990

The ringed X-galaxy NGC 7020

The southern SO (sup +) galaxy NGC 7020 presents an unusual morphology: it includes a very regular outer ring which is completely detached and which envelops an inner ring/lens zone with a hexagon surrounding an X shape. The outer ring has a high contrast compared to those usually observed in barred galaxies, yet NGC 7020 is not obviously barred. The morphology of this galaxy poses an interesting puzzle in that the hexagonal/X zone is not a typical type of feature to find in the interior of such a regular ring. Instead, the zone bears a striking resemblance to the edge-on galaxy IC 4767, recently studied by Whitmore and Bell (1988 = WB88) and dubbed by them as the X-galaxy because its inner regions appear to be crossed by two distinct enhancements lined at plus or minus 22 deg with respect to the major axis. The observation of a similar phenomenon in NGC 7020 is interesting because of the suggestion by WB88 that X structures could be related to accretion of matter associated with a merger or tidal encounter between an SO and a small satellite galaxy. If this interpretation is correct for NGC 7020, then it has important implications for the nature of the outer ring. An alternative interpretation is that the inner hexagonal/X zone is a region where resonant periodic orbits in a weak bi-symmetric potential perturbation are influencing the morphology more strongly than might be expected. A brief summary of a more extensive paper (Buta 1990c = B90c) and a few other details concerning this interesting galaxy are given.

Buta, Ronald↗

NASA NTRS1976

Ring current loss mechanisms and composition as inferred from equatorial pitch angle distributions observed during a storm recovery phase

Explorer 45 measurements of pitch angle distributions (PAD's) of ring current ions were examined for evidence of charge exchange or pitch-angle diffusion as loss mechanisms for the ring current during a storm recovery phase. The observed rounding of the PAD's above a minimum parallel energy is seen as resulting from pitch angle diffusion driven by resonant interactions with ion cyclotron waves. Calculations of growth rates using observed ion fluxes and PAD's have shown that ion cyclotron waves can be significantly amplified by the ring current plasma. However, wave growth off the equator must be taken into account in order to understand the time evolution of the observed PAD's. Isotropic distributions at lower energies remain isotropic at L-values between 3 and 4 despite the presence of charge exchange losses. An explanation for this apparent inconsistency may be that ring current is dominated by some ion species other than protons during recovery phase.

Lyons, L. R.↗

NASA NTRS1993

Mass of Saturn's A ring

The mass of Saturn's A ring is reestimated using the behavior of spiral density waves embedded in the ring. The Voyager photopolarimeter (PPS) observed the star delta-Scorpii as it was occulted by Saturn's rings during the Voyager 2 flyby of Saturn in 1981 producing a radial profile of the rings. We examined forty spiral density waves in the Voyager PPS data of the A ring including 10 weaker waves that have not been previously analyzed by means of an autoregressive power spectral technique called Burg. The strengths of this new method for ring studies are that weaker, less extended waves are easily detected and characterized. This method is also the first one which does not require precise knowledge of the resonance location and phase of the wave in order to calculate the surface mass density. Uncertainties of up to 3 km are present in the currently available radial scales for Saturn's rings.

Horn, L. J.↗

NASA NTRS1985

Investigations of Planetary Ring Phenomena

The structure of Jupiter's rings was studied in an effort to understand the processes that generate the rings. The faint material in the Saturn system was investigated leading to the discovery of a new ring and a way to interpret the wavy features surrounding Encke's division in terms of perturbing moonlets. The interaction of faint rings and magnetospheres helped identify some of the charged particle absorbers seen by Pioneer 11 in the neighborhood of the F ring. Angular momentum drain might account for the slow rotations of intermediate sized asteroids. Much of the Jovian ring structure can be understood in terms of debris loss from satellites, rapid orbital evolution, resonance, and charged dust dynamics.

Burns, J. A.↗

NASA NTRS1989

Theory of the pulse response from a small antenna in a magnetized plasma

The electrostatic plasma response to a small pulsed antenna in a magnetic field is analyzed. The ringing of the plasma at three discrete frequencies--the upper-hybrid frequency and two resonance cone branch frequencies--is evidenced, and the amplitudes of these frequency responses is determined as a function of the characteristic plasma frequencies, the angle of observation with respect to the magnetic field, and the pulse length. Applications to plasma diagnostics are discussed. It is shown that the upper hybrid response and the response at either of the resonance cone branch frequencies is adequate information to determine the plasma density, and the magnetic field magnitude and angle.

Grabbe, Crockett L.↗

NASA NTRS1990

Models of Neptune's arc rings

Models proposed to explain the dynamical confinement of such structures as incomplete arc rings in orbit about the planet Neptune are reviewed and tested against the currently available observational data. It is shown that satellites can confine arc rings to very limited radial and azimuthal extents via a combination of corotation and Lindblad resonances. The resonances can be produced by the same moon or by different moons.

Lissauer, Jack J.↗

NASA NTRS1991

Charged dust dynamics - Orbital resonance due to planetary shadows

The dynamics of a weakly charged dust grain orbiting in the equatorial plane of a planet surrounded by a rigidly corotating magnetospehre is examined. It is shown that an introduction of an effectilve 1D potential causes a perturbation due to electrostatic forces, which induces a motion of the pericenter, similar to the effect of the planetary oblateness. A case is examined where the charge varies periodically due to the modulation of the photoelectron current occurring as the grain enters and leaves the planetary shadow, causing the electromagnetic perturbation to resonate with the orbital period and to modify the size and eccentricity of the orbit. This effect is demonstrated both numerically and analytically for small grains comprising the Jovian ring, showing that their resulting changes are periodic, and their amplitude is much larger than that of the periodic changes due to light-pressure perturbation or the secular changes due to resonant charge variations that develop over a comparable time span.

Horanyi, M.↗

NASA NTRS1970

A unified theory of stable auroral red arc formation at the plasmapause

A theory is proposed that SAR-arcs are generated at the plasmapause as a consequence of the turbulent dissipation of ring current energy. During the recovery phase of a geomagnetic storm, the plasmapause expands outward into the symmetric ring current. When the cold plasma densities reach about 100/cu cm, ring current protons become unstable and generate intense ion cyclotron wave turbulence in a narrow region 1/2 earth radius wide (just inside the plasmapause). Approximately one-half of the ring current energy is dissipated into wave turbulence which in turn is absorbed through a Landau resonant interaction with plasma spheric electrons. The combined thermal heat flux to the ionosphere due to Landau absorption of the wave energy and proton-electron Coulomb dissipation is sufficient to drive SAR-arcs at the observed intensities. It is predicted that the arcs should be localized to a narrow latitudinal range just within the stormtime plasmapause. They should occur at all local times and persist for the 10 to 20 hour duration of the plasma-pause expansion.

Cornwall, J. M.↗

NASA NTRS1985

A dual frequency microstrip antenna for Ka band

For fixed satellite communication systems at Ka band with downlink at 17.7 to 20.2 GHz and uplink at 27.5 to 30.0 GHz, the focused optics and the unfocused optics configurations with monolithic phased array feeds have often been used to provide multiple fixed and multiple scanning spot beam coverages. It appears that a dual frequency microstrip antenna capable of transmitting and receiving simultaneously is highly desirable as an array feed element. This paper describes some early efforts on the development and experimental testing of a dual frequency annular microstrip antenna. The antenna has potential application for use in conjunction with a monolithic microwave integrated circuit device as an active radiating element in a phased array of phased array feeds. The antenna is designed to resonate at TM sub 12 and TM sub 13 modes and tuned with a circumferential microstrip ring to vary the frequency ratio. Radiation characteristics at both the high and low frequencies are examined. Experimental results including radiating patterns and swept frequency measurements are presented.

Lee, R. Q.↗

NASA NTRS1985

Monolithic, unidirectional single-mode Nd:YAG ring laser

A new solid-state laser has been designed which achieves high single-mode output power by using a unidirectional nonplanar resonator constructed from a single Nd:YAG crystal. When placed in a magnetic field, the laser provides a pump-limited, single-axial-mode output of 163 mW at 1064 nm. The laser has been specifically developed as an oscillator for a long-range coherent Doppler anemometer. Other applications include coherent communications, coherent optical radar, and inertial rotation sensing.

Kane, T. J.↗

NASA NTRS1996

Visualization of High Latitude Ion Upflow in Support of the Image Mission

The study of the magnetosphere is a 400 year old science that began with the publication by Gilbert, in 1600, of his hypotheses that the Earth was a giant magnet. Since then we have learned many things about the magnetosphere, particularly in the last 40 years of the space age, but we still have many unanswered questions. In spite of the many thousands of observations of this system we still lack a global understanding of how it works. This is due to its large size and tenuous nature that mean that any measurement made of the fields or particles involved only give one a knowledge of the local conditions at a given time. To gain a global perspective through such observations would require the simultaneous operation of thousands of satellites spread throughout the magnetospheric system in addition to observations made on the ground. Such a program would be impractical at least from financial considerations. What is needed for the advancement of magnetospheric physics is to develop the same capabilities that astrophysicists, solar physicists and meteorologists have been using for years --- the ability to stand back from the object under study and see it in its entirety. The challenge for doing this for the magnetosphere is that the particle densities are very low and the material is, for the most part, not luminous. In the last 25 years several ideas have been proposed that would allow at least the imaging of certain portions of the magnetosphere. These include imaging of the plasmasphere through the resonant scattering of solar 304 A from He+ ions, imaging of various hot plasma populations (i.e. the ring current, plasmasheet, upflowing ionospheric ions, etc.) from the neutral atoms that result when ions of these populations charge exchange with the hydrogen geocorona, and imaging the aurora at various wavelengths in the far ultraviolet. In addition, a novel technique for probing various boundaries in the magnetosphere by bouncing low frequency radio waves off of them has been extensively studied. Such a technique is analogous to the way the under water world can be probed with sonar. About five years ago NASA convened a science working group to study the possibility of flying a magnetospheric imaging mission. This resulted in a number of proposals for such a mission, one of which was selected to be the first MIDEX mission, to be launched in early 2000. The mission is called IMAGE (Imager for Magnetopause to Aurora Global Exploration) and its P.I. is J. Burch at SwRI. The IMAGE spacecraft will carry imagers to view the plasmasphere, aurora, ring current, inner plasmasheet, and upflowing ionospheric ions as well as a radio sounder to probe the location, shape and dynamics of the magnetopause, plasmapause, etc. Between its selection last April and the non advocacy mission review, which takes place next spring, the IMAGE teams needs to further refine the design of the mission and its instruments. The theory and modeling (T&M) subgroup of this team has the task of demonstrating what kind of images the instruments on IMAGE will see as well as showing that useful scientific information can be extracted from such images. As a central element to the efforts of the T&M subgroup we have decided to simulate and create synthetic images for the magnetic cloud event of October, 1995. In this event a large cloud, with high plasma densities and strong magnetic fields, ejected from the sun collided with the earth's magnetosphere triggering a three day period of intense magnetic storms and substorms. This event was observed from a number of different spacecraft and on the ground so we have a good data set to work with. In our work we will place the IMAGE spacecraft in the magnetosphere on its proposed orbit, with its proposed instruments, to see what it would see had it been there. Existing models of the plasmasphere, ring current and magnetopause will be run for this event to give the structures for the imaging instruments. There are several models which are lacking and which need to be developed. These include a model for the cusp, the inner plasmasheet and the upflowing ions. My task this summer was to develop the upflowing ion model and use it to create synthetic images.

Wilson, Gordon R.↗

NASA NTRS2008

A Large, Free-Standing Wire Grid for Microwave Variable-delay Polarization Modulation

One technique for mapping the polarization signature of the cosmic microwave background uses large, polarizing grids in reflection. We present the system requirements, the fabrication, assembly, and alignment procedures, and the test results for the polarizing grid component of a 50 cm clear aperture, Variable-delay Polarization Modulator (VPM). This grid is being built and tested at the Goddard Space Flight Center as part of the Polarimeter for Observing Inflationary Cosmology at the Reionization Epoch (POINCARE). VPMs modulate the polarized component of a radiation source by splitting the incoming beam into two orthogonal polarization components using a free-standing wire grid. The path length difference between these components is varied with a translating mirror, and then they are recombined. This precision instrumentation technique can be used to encode and demodulate the cosmic microwave background's polarization signature. For the demonstration instrument, 64 micrometer diameter tungsten wires are being assembled into a 200 pm pitch, free-standing wire grid with a 50 cm clear aperture, and an expected overall flatness better than 30 micrometers. A rectangular, aluminum stretching frame holds the wires with sufficient tension to achieve a minimum resonant frequency of 185 Hz, allowing VPM mirror translation frequencies of several Hz. A lightly loaded, flattening ring with a 50 cm inside diameter rests against the wires and brings them into accurate planarity.

Voellmer, George↗

NASA NTRS2010

Observing Supernova 1987A with the Refurbished Hubble Space Telescope

The young remnant of supernova 1987A (SN 1987A) offers an unprecedented glimpse into the hydrodynamics and kinetics of fast astrophysical shocks. We have been monitoring SN 1987A with the Hubble Space Telescope (HST) since it was launched. The recent repair of the Space Telescope Imaging Spectrograph (STIS) allows us to compare observations in 2004, just before its demise, with those in 2010, shortly after its resuscitation by NASA astronauts. We find that the Ly-alpha and H-alpha lines from shock emission continue to brighten, while their maximum velocities continue to decrease. We report evidence for nearly coherent, resonant scattering of Lya photons (to blueshifts approximately -12,000 km /s) from hotspots on the equatorial ring. We also report emission to the red of Ly-alpha that we attribute to N v lambda lambda 1239,1243 Angstrom line emission. These lines are detectable because, unlike hydrogen atoms, N4+ ions emit hundreds of photons before they are ionized. The profiles of the N v lines differ markedly from that of H-alpha. We attribute this to scattering of N4+ ions by magnetic fields in the ionized plasma. Thus, N v emission provides a unique probe of the isotropization zone of the collisionless shock. Observations with the recently installed Cosmic Origins Spectrograph (COS) will enable us to observe the N v lambda lambda 1239,1243 Angstrom line profiles with much higher signal-to-noise ratios than possible with STIS and may reveal lines of other highly ionized species (such as C IVlambda lambda 1548,1551 Angstrom) that will test our explanation for the N v emission

France, Kevin↗

NASA NTRS2023

A Recent Impact Origin of Saturn’s Rings and Mid-Sized Moons

Saturn’s rings appear to be remarkably young, ∼100 Myr old, ruling out most previous hypotheses for their origin and incentivising new explanations. This could include a recent formation also for at least some of Saturn’s mid-sized icy moons. We present high-resolution SPH simulations that reveal how a range of collision scenarios driven by recent resonant instabilities in a precursor satellite system can scatter large masses of fragments and debris throughout the system that could evolve to both form the rings and reaccrete into present-day moons.

J Kegerreis↗

NASA NTRS1982

The gravito-electrodynamics of charged dust in planetary magnetospheres

The orbital dynamics of small electrically charged dust grains within the corotating regions of planetary magnetospheres is considered. Equations are derived for the elliptical epicyclic motion of positively and negatively charged particles about the guiding center in an equilibrium circular orbit under the influence of small perturbations. Those orbits that are stable to the perturbations are found to have a ratio of the semiaxes of the epicycle between 1/2 and 1, depending on the specific charge, and a gyration frequency about the guiding center between the Kepler frequency and the grain gyrofrequency in a nonrotating frame. In the magnetospheres of Jupiter and Saturn, where the grains are expected to be negatively charged and move in a prograde sense, the guiding centers are predicted to have speeds intermediate to the Kepler speed and the corotation speed and thus may undergo a 1:1 magneto-gravitational resonance with a neighboring satellite. Results may be used in the interpretation of the waves in the F ring of Saturn in terms of the dust size distribution.

Mendis, D. A.↗

NASA NTRS1989

A solar system dust ring with earth as its shepherd

Numerical integrations are used here to show that small dust grains can be temporarily captured into exterior orbit-orbit resonances with the earth, lasting from less than 10,000 years to more than 100,000 years. Grains with radii of 30-100 microns, orbiting in planes less than 10 deg from the plane of the solar system and with orbital eccentricities of less than 0.3, are captured most easily. It is argued that there should be an approximately toroidal cloud of particles, derived mostly from the asteroid belt, trapped into a variety of these exterior resonances. The cloud is mostly beyond the earth's orbit, but includes it.

Jackson, A. A.↗