Tides due to orbital eccentricity may have a substantial effect on the rotation and tectonics observed on Jupiter's moon, Europa. A direct measurement of Europa's rotation rate has been made by measuring the positions of surface features relative to the terminator in both Voyager and Galileo images. From these measurements I have found that the rotation of Europa relative to the direction of Jupiter is <0.5° over a 17 year period, i.e. one rotation with respect to Jupiter would require at least 12,000 years. Non-synchronous rotation is also a significant source of global stress which, combined with the diurnal tidal stress, provides a failure mechanism resulting in tensile cracks on a global scale. The stress associated with rotational and diurnal tides can also explain the orientations and age relationships observed regionally in Europa's northern hemisphere. Additional global scale linear features also strongly correlate to these stress fields suggesting that they too may have also formed as cracks. After crack formation, diurnal tides may significantly affect the evolution of cracks through either ridges formation, regional extension, or strike-slip motion. The process of tidal shear displacement is analagous to actual walking. Mapping of five different regions on Europa has revealed 121 strike-slip faults. Based on these observations, Europa appears to support the formation of right-lateral faults in the southern hemisphere and left-lateral faults in the northern hemisphere. The theory of tidal walking predicts exactly that dichotomy on average over the hemispheres. Additionally, all of the mapped strike-slip faults were associated with double ridges and bands, but none were detected along cracks. Thus, cracks (even older ones) without ridges apparently have not generally penetrated to a decoupling layer, consistent with models for ridge formation that require cracks to penetrate to a liquid water ocean.

We study thermally induced density perturbations during inflation. This scenario is characterized by two thermodynamic conditions: (i) the primordial perturbations originate in the epoch when the inflationary universe contains a thermalized heat bath; (ii) the perturbations of the inflationary scalar field are given by the fluctuation-dissipation relation. We show that (1) the power spectrum of the primordial density perturbations follows a tilted power law behavior; (2) the relation between the amplitude and the power index of the spectrum exhibits a "thermodynamic" feature--it depends mainly on the thermodynamic variable M, the inflation energy scale; (3) both the adiabatic mode and the isocurvature mode of density perturbations appear during the inflation epoch, and the resultant power spectrum on super-horizon scales is substantially suppressed. These results are found to be very consistent with observations of the temperature fluctuations in the cosmic microwave background if the energy scale of the inflation is about 10¹⁵-10¹⁶ GeV.

I have used the SALE2D hydrocode to study spall in impacts into layered terrains. Application of my results to the problem of martian meteorite provenance resolves two outstanding paradoxes. First, the minimum size crater previously thought to be required to eject martian meteorites is so large (12 km) that it is highly unlikely such an event occurred on shergottite age terrain in the last few million years. The geochemical evidence supports four launch events. This issue I have resolved by establishing a new lower limit to the minimum size crater of 3 km. Second, the martian meteorites are dominated by shergottites (62%) which come from the youngest and apparently rarest martian terrains. The vast majority of Mars appears to be under represented. This paradox lies on the false premise that all terrains are equally efficient in launching material during an impact. I have found that the presence of a weak, low density layer suppresses spall velocity and increases shock pressures in an impact. Since the regolith on Mars can be expected to be largely impact-generated, the older terrains are covered by a greater depth of regolith. Qualitatively, older terrains are under represented in the martian meteorites because they require larger (rarer) impacts to launch material into space. I have shown this quantitatively for shergottites, nakhlites, and Chassigny. An extension of my work provides some constraints on the extent of martian ancient terrain.

The solar system began with the collapse of a dense molecular cloud, which is rich in atoms, dust grains and diverse molecules. The complexity of different physical and chemical processes which happened during the formation of the early solar system constitute a major topic within our scientific community, even though a complete model of the solar nebula including all such processes has not been constructed. This thesis deals with some of these chemical and physical processes and consists of two phases. In the first phase of my work, I have studied the heating of water-ice grains during infall into the solar nebula from the surrounding collapsing cloud. The investigations in this phase extend previous studies (Lunine et al., 1991) in two aspects. Firstly, we revise the previous grain heating model. The calculations for large fluffy grains (up to 10μm) are conducted. Secondly, we explicitly incorporate terms associated with various exothermic and endothermic reactions which contribute to the thermal evolution of the grains in our computation. By tracking the threshold temperatures reached as a function of grain size, density and infall velocity, we are able to quantify the evolution of infalling interstellar grains. Once the volatiles were brought in by the ice grains, codeposition of diversed volatiles on the surface of refractory grains happened in the cold solar nebula region. Disk dynamical evolution leads to a background temperature below 50K at distance beyond 20AU. Studies have shown that amorphous water ice forms at this temperature range. Amorphous ice can volumetrically absorbs a large amount of volatiles. My work in the second phase consists of investigations of amorphous water ice, especially its property of trapping various volatiles under conditions well outside the stability field of the condensed phases of the volatiles. A statistical thermodynamical model has been established. It is used to predict fractional abundances of trapped volatiles in different temperature and pressure conditions. Our investigations involve both theoretical and experimental studies.

A new technique for ground based photometric helioseismology has been implemented. The technique is able to detect low amplitude oscillations in the solar irradiance by making simultaneous measurements at continuum wavelengths of 0.507 μm, 0.747 μm, and 1.600 μm. Data is collected from a rectangular region covering approximately 57% of the solar disk, extending ±0.30 R(⊙) about the solar rotational axis, and ±0.38 R(⊙) about the solar equator, using square pixels varying in linear size from 0.032 R(⊙) to 0.053 R(⊙). A differential spatial filter is applied, taking advantage of cancellations of undesired variations and forming a signal which is sensitive to most modes with spherical harmonic index l ≤ 7. Linear combinations are made of the three solar signals and the telescope internal Temperature signal, mitigating the deleterious effects of the terrestrial atmosphere and of local temperature variations. Frequencies of local maxima in the Power Spectrum of the residual signal, in the 400 μHz to 850 μHz range, are found to be consistent with those determined by solar limb profile measurements made in 1979. The measured coincidence levels indicate that the probability that the 1979 and 1999 data sets are random with respect to one another is approximately 5 x 10⁻⁹. Frequency shifts between the 1979 data and the 1999 data, possibly related to the solar activity cycle, are found: δν(n=1;l=4,...,7) = -0.16 ± 0.01 μHz, δν(n=2;l=3,...,7) = -0.04 ± 0.01 μHz, and δν(n=3;l=2,...,4) = -0.11 ± 0.01 μHz.

This dissertation reports on the first "5-minute" solar oscillation observations obtained with the Photometric Telescope, an instrument constructed in the Department of Physics at the University of Arizona. The instrument is designed to simultaneously acquire spatially resolved intensity images of the solar surface at three wavelengths in the solar continuum: 507 nm, 747 nm, and 1600 nm. Images were recorded at an approximate 30 second cadence, weather permitting, for an approximate 3 month duration during the Spring of 1999. A central rectangular region of the solar disk spanning ±0.53 R(⊙) in a direction parallel to the solar equator and ±0.636 R(⊙) in a direction parallel to the solar axis is used in obtaining the "5-minute" results. Differential spatial filters utilizing the natural logarithm are developed. Proper design of these filters allows great reductions in the sensitivity to terrestrial atmospheric fluctuations as well as instrumental noise sources such as image fitter. The processing techniques utilized allow the simultaneous observation of solar oscillations in the 2500 to 3600 μHz region at each of the three instrumental wavelengths. The spatial filters used have high sensitivity to modes in the ℓ = 4 to ℓ = 8 range. One-day power spectra from 40 long observing days are averaged. Concurrent data from the SOHO satellite's Luminosity Oscillation Imager is analyzed in a similar manner showing results in outstanding agreement with the Photometric Telescope spectra. Further comparison of measured power spectra peak locations with theoretically predicted peak locations verifies the Photometric Telescope as a capable helioseismology instrument. New "5-minute" oscillation results are also presented. The amplitudes of the individual "5-minute" oscillations are on the order of 10-100 ppm, in agreement with previous amplitude measurements. While these amplitudes vary greatly depending on the details of the stochastic excitation, the oscillation amplitude ratios and phase differences of solar oscillations for the 507 nm, 747 nm, and 1600 nm wavelengths can be measured with a high degree of accuracy. This dissertation reports the first such measurements. The amplitude ratios (I'/I)₇₄₇/(I'/I)₅₀₇ ∼ 0.6 and (I'/I)₁₆₀₀/(I'/I)₅₀₇) ∼ 0.25 are found to be independent of frequency over the frequency region studied and nearly independent of the angular degree of the mode. By contrast, the relative phase differences (φ₇₄₇ - φ₅₀₇) and (φ₁₆₀₀ - φ₅₀₇) are found to have a significant frequency dependence and to depend somewhat sensitively on the angular degree of the mode. The measured wavelength dependent amplitude and phase relationships provide an invaluable diagnostic tool which can be used in future work to help identify longer period and lower amplitude oscillatory modes.

The evolution of low- and intermediate-mass stars (1M(⊙) - 8M(⊙)) from the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PN) phase is a poorly understood phase of stellar evolution. We have observed a sample of AGB stars, Proto-Planetary and Planetary Nebulae (PPNe and PNe) at thermal-infrared and millimeter wavelengths. The thermal-infrared emission comes from the warm dust (T(dust) ≈ 100-300 K) circumstellar shells. Images at these wavelengths provide a unique "close-up" look at the morphology of these sources, and therefore allow us to constrain the geometry and/or mass loss rates on short dynamical timescales. The millimeter-wave observations probe the extended circumstellar molecular envelopes; therefore they provide valuable spatial and kinematical information on the larger scales (and over longer dynamical timescales) than the mid-IR images. Our results show that the dust shells of all the planetary and proto-planetary nebulae (PPNe and PNe) in our study are not spherical; those that are well-resolved appear to be bipolar and can be modeled with axially symmetric models. They strongly suggest that the evolution from AGB to PN is often accompanied by higher mass loss rates in the equatorial plane than in the polar regions, as predicted by binary star (common envelope) evolution models, or models involving stellar rotation. At least one bipolar nebula (M 4-18) appears to be a single, low-mass star. From our mid-IR images at feature wavelengths we find that the spatial distribution of the carbonaceous and silicate grains varies over the surface of the nebulae. IC 5117 shows evidence for stratification of carbon- and oxygen-based grains and suggests that some PNe go through temporal changes in circumstellar chemistry (from oxygen-rich to carbon-rich) as they evolve off the AGB. The molecular envelopes of the sources in our study can be modeled with spherically symmetric models though two sources (IRC + 10216 and AFGL 2343) show kinematical and spatial evidence for departures from spherical symmetry. Our millimeter observations of IRC + 10216 also provide confirmation that the interstellar UV photons initiate a variety of photochemical reactions in circumstellar envelopes of AGB stars and PNe.

FASTTRAC (Fast Adaptive Secondary for Tip-Tilt Removal by Automatic Centroiding) is a tip-tilt secondary system which increases the angular resolution of images taken at Steward Observatory's 90" Bok and 61" Bigelow telescopes. K band imagery is gathered with the facility infrared camera and wavefront sensing is done with a small format charge-coupled device (CCD). I examine desirable characteristics of wavefront-sensing CCDs and evaluate the performance of the device used in FASTTRAC according to those criteria. The main drawback of the device is its low quantum efficiency due to frontside illumination. The read noise of the system is adequate, particularly for FASTTRAC which is generally assigned to bright time. The increased angular resolution provided by FASTTRAC is desirable for imaging crowded fields, such as those found in Local Group galaxies. Stellar photometry is a more powerful tool for studying the structure of these galaxies than is surface photometry, in which the light from all types of stars is mixed together. In particular, the distribution of old stars is representative of the underlying mass distribution, so these stars may be used to measure the overdensity in the arms of spiral galaxies. FASTTRAC was used to observe fields in M33, the nearest spiral which is not seen edge-on. These fields were observed in a range of seeing conditions and with guide stars of varying magnitudes and positions relative to the fields of interest. I analyze the performance of FASTTRAC in these varying conditions and offer some advice to future FASTTRAC observers. I also analyze the crowding in the M33 fields and conclude that, to K∼16.5, it does not vary significantly with placement in or outside of a spiral arm. Therefore a coarsely-sampled, wide field survey of the populations of M33 will not be systematically biased by crowding. Therefore a survey covering 35' by 25' was conducted in I and K bands, covering all of M33 out to a deprojected radius of 16'. The resulting star catalogs reach a depth of about I=21.5 and Ks When plotted on a color-magnitude diagram, these stars separate into a young population of red supergiants and an older population of red giants. The giants are old enough to have experienced many orbits and are thus representative of the mass distribution of the galaxy. The fraction of K-band light which is "young" is only 5-10% indicating that surface photometry in general would not be terribly biased, but there are local variations in which the young component is much stronger. Fourier decomposition of the old catalog reveals significant amplitudes (up to 0.5), indicating that the galaxy does indeed contain local overdensities, which supports the basic idea of spiral density wave theory. The strongest component in M33 is one-armed or lopsidedness, with some power in the two-armed component and much less in the higher-order components. The two-armed component may in fact represent a bar in the inner few arcminutes.

The purpose of this study is to understand the space density and properties of active galaxies to z &sim;eq 0.8. We have investigated the frequency and nature of unresolved nuclei in galaxies at moderate redshift as indicators of nuclear activity such as Active Galactic Nuclei (AGN) or starbursts. Candidates are selected by fitting imaged galaxies with multi-component models using maximum likelihood estimate techniques to determine the best model fit. We select those galaxies requiring an unresolved, point source component in the galaxy nucleus, in addition to a disk and/or bulge component, to adequately model the galaxy light.

In this dissertation the results of a ten-year spectrophotometric survey of comets are presented. By measuring in a systematic way the production rates of C₂ NH₂, CN, and H₂O released from the nucleus, we sought to explore comet-to-comet variations that may yield clues to conditions in the early solar nebula. We classify our observed comets into four taxonomic classes (Type I, II, III, IV). The two classes which comprise the great majority of our sample (Type I and II) were also discerned in the recent survey by A'Hearn et al. (1996) and in general can be thought of as "normal" and "C₂ depleted" comets. It is argued that the "normal" comets in general originate in the inner comet forming regions at the distances of Uranus and Neptune whereas the "C₂ depleted" may originate in the inner edge of the Kuiper disk. Evolved from our interest in extinct cometary candidates, we present the results of out near-Earth asteroid spectroscopy survey. Though taken at a wavelength range that makes firm classification difficult (0.5-1.0μm) we find that in general our sample is much closer spectroscopically to the ordinary chondrites and basaltic achondrites than to the spectra of main-belt asteroids, firming the link between near-Earth asteroids and meteorites.