ALBERT

Description: The International Cometary Explorer (ICE) encounter with Comet Giacobini-Zinner took place 7 years after the spacecraft's original launch on 12 August 1978 as the International Sun Earth Explorer 3 (ISEE-3), part of a three-spacecraft project to study the interaction between the solar wind and the Earth's magnetosphere. Transfer to an interplanetary trajectory was performed via a 119-km-altitute, gravity-assist, lunar swingby on December 1983. Navigation support during interplanetary cruise and comet encounter was provided by orbit determination utilizing radio metric data from the DSN 64-meter antennas in Goldstone, California and Madrid, Spain. Orbit solutions yielding predictions of 50-km geocentric delivery accuracy in the target aim plane were achieved during interplanetary cruise and at comet encounter using 6-to-12-week data arcs between periodic attitude-change maneuvers. One-sigma two-way range and range rate residuals were consistently 40 meters and 0.2 mm/s or better, respectively. Non-gravitational forces affected the comet's motion during late August and early September 1985 and caused a 2300-km shift in the orbit of the comet relative to the spacecraft. This necessitated a final ICE orbit trim maneuver 3 days prior to encounter. Near-real-time assessment of two-way 2-GHz (S-band) Doppler pseudo-residuals during the June and July 1985 trajectory change maneuvers aided in calibration of the spacecraft's thrusters in preparation for this final critical maneuver. Post-flight analysis indicates tail centerline passage was achieved within 10 seconds of the predicted time and geocentric position uncertainty at encounter was less than 40 km.

Description: Final revisions were made in the study of continuum spectrophotometry of 17 comets done at Lick Observatory. Changes based upon this study were introduced into the Divine-Newburn cometary modelling paradigm. Work was begun on modifications to all of the theory based upon the direct nucleus and coma observations made by the Halley space missions.

Description: Spectroscopic and spectrophotometric data on the atmospheres of comets, the outer planets, and Titan at ultraviolet to near-infrared wavelengths were acquired. These data support an effort aimed at characterizing the physical properties and distribution of aerosol particles in the atmospheres of these bodies. New spectrophotometry was acquired of Uranus at 0.2 lambda 0.3 micrometer with IUE; archival IUE spectrophotometry of Uranus and Neptune in this wavelength range was acquired and recalibrated. New estimates of radiometric Bond albedos and global energy budges of Uranus, Neptune and Titan were published.

Description: An Atlas of Comet Halley 1910 II photographs and spectra is being prepared. The major section consists of 838 photographic observations from fifteen observatories around the world. Multiple images of many photographs are reproduced to bring out detail in the near nucleus region, in the coma and in the tail. The Atlas contains a total of 1209 photographic images of the 1910 apparition. In addition there are sections showing drawings from 1935 and 1910. A short section compares 1910 drawings and photographs. The final two sections display digitally processed images from 1910 and 1910 spectra. A three part appendix contains diagrams of various data associated with the 1910 apparition, a set of tables of all 1910 images and a bibliography.

Description: Infrared observations were made of the outer planet satellites. These data provide vital information about the thermophysical properties of satellite surfaces, including internal heat sources for Io. Observations include both broad and narrow band measurements in the 2 to 20 micrometer spectral range. Types of observation and target priority were determined to make maximum use of existing data from Voyager and other missions, on-going and planned missions such as Galileo, were supported and techniques and data for planning new missions and instrumentation were developed.

Description: Several processed polycyclic aromatic hydrocarbons (PAH) samples were produced to date. The Raman spectra and D/H ratios of these samples will be studied in the near future. A manuscript was sent to Icarus which gives a detailed discussion of the possibility of using solar flare tracks in interplanetary dust particles (IDPs) to determine a cometary vs. asteroidal source of the IDPs. The technique looks promising and a program was started to measure the large number of IDP track density necessary to address the issue of the source(s) of the dust. The results could potentially tell a great deal about comets and/or asteroids.

Description: Over the past 3 years, a series was obtained of the CCD images of regions surrounding young stellar objects (YSO's) located in a variety of environments with the goal of providing a census of the properties of mass outflows associated these objects. A catalog describing the optical morphology and kinematics of 38 mass outflows associated with young stellar objects (YSOs) was completed. The direct detection was reported of disks surrounding HL Tau and LI551/IRS 5 -- both sources of optical jets and large-scale mass outflows. In each case, the disk dimensions are on the order of several hundred astronomical units and the disk dust masses approximately 10 to the -7th power solar masses. A program aimed at indirect detection of circumstellar disks associated with YSOs was started. The technique involves comparison of an observed bolometric luminosity (L(bol)) with an independent measure of the true luminosity (L(spec)) of a YSO which derives from the observed strengths of surface-gravity-sensitive spectral features.

Description: In order to provide observers with accurate cometary ephemerides, up-to-date astrometric positions must be used to update the existing orbit and ephemeris for each object. In addition, nongravitational forces must be taken into account; these forces are assumed due to the rocket effect of outgassing cometary ices. Once successfully modeled, the cometary nucleus spin direction, spin axis evolution, and the volatility of the nucleus ices can be inferred. The predicted ephemerides also become far more accurate.

Description: Stars are observed with a ground-based instrument designed to measure small changes in the line-of-sight velocities. The purpose of the observations is to detect large planets by the oscillatory reflex motion they induce on the stars they are orbiting. The instrument is an optical spectrometer for which wavelengths are first calibrated by transmission through a tunable Fabry-Perot etalon interferometer. Changes in the line-of-sight velocities are revealed by changes in the Doppler shift of the absorption-line spectra of stars. The scrambling of incident light by an optical fiber and the stability of wavelength calibration by a tilt-tunable Fabry-Perot etalon provide immunity to systematic errors that historically have effected more conventional radial velocity spectrographs. A cross-dispersed echelle spectrograph spatially separates the orders of constructive interference transmitted through the etalon. Selecting several echelle diffraction orders in the vicinity of 4250 to 4750 A, which are imaged on a CCD, about 350 points on the profile of the stellar spectrum are sampled by successive orders of interferometric transmission through the etalon.

Description: Telescopic observations were made of gases and plasmas in the Jupiter system, and related phenomena such as the recently-discovered sodium atmosphere of Mercury. Sodium absorption in Io's atmosphere was observed to distances as large as 5 Io radii during the mutual-eclipse season of the Jovian satellites. Analysis of Jovian disk spectra has proceeded, as planned, from an emphasis on the H2 ortho-para ratio to analysis of methane absorptions and determination of cloud structure. Several 2-channel photometers were constructed in 1978 for the Uranus event at which the rings were discovered and a smaller, single-channel unit was built more recently. Although the photometers themselves are still fully usable, the data-acquisition systems have major deficiencies.

Description: It is proposed to measure the reflectance spectra of the icy satellites of Jupiter, Saturn and Uranus in the spectral region 1.8 to 2.4 micrometers. These observations use the new Cooled Grating Array Spectrometer using a 32-element InSb photodiode array detector and produce spectra of higher resolution and precision than any data yet obtained; the ultimate scientific objective is to search for the signatures of methane clathrate, ammonium hydroxide or carbon monoxide clathrate (compounds predicted to exist on icy surfaces in the outer solar system by several theories of formation of these bodies) in the region of the spectrum where water ice has a relative maximum in reflectance. At the very least, these data will allow upper limits to be placed on the amount of these chemical species that can be present. The specific targets is Europa, Ganymede, Enceladus, Ariel and Titania, bodies that have the highest probability of having some or all of these volatiles on their surface according to current formation models.

Description: In order to understand the origin and distribution of the biogenic elements and their compounds in the solar system, it will be necessary to study material from many classes of objects. Chemical, elemental, and isotopic measurements of returned samples of comets, asteroids, and possibly extra-solar system dust clouds would provide information on a particularly important class: the primitive objects. Extraterrestrial micron-sized particles in the vicinity of earth are one source of such materials that might otherwise be inaccessible. The Space Station appears to be an eminently suitable platform from which to collect and detect these various particles. The primary challenge, however, is to collect intact, uncontaminated particles which will be encounted at tens of kilometers per seconds. A concept for a micrometeoroid detector that could be deployed at a Space Station has been developed which uses a large area detector plate implanted with acoustic transducers. When an impact event occurs, the resulting signal is subjected to spectral analysis providing positive detection, momentum information, and angle of incidence. The primary advantage of this detector is the large area which increases the probability of measuring events.

Description: The recent Voyager flyby of Titan produced evidence for at least nine organic compounds in that atmosphere that are heavier than methane. Several models of Titan's atmosphere, as well as laboratory simulations, suggest the presence of organics considerably more complex that those observed. To ensure that the in situ measurements are definitive with respect to Titan's atmosphere, experiment concepts, and the related instrumentation, must be carefully developed specifically for such a mission. To this end, the possible composition of the environment to be analyzed must be bracketed and model samples must be provided for instrumentation development studies. Laboratory studies to define the optimum flight experiment and sampling strategy for a Titan entry probe are currently being conducted. Titan mixtures are being subjected to a variety of energy sources including high voltage electron from a DC discharge, high current electric shock, and laser detonation. Gaseous and solid products are produced which are then analyzed. Samples from these experiements are also provided to candidate flight experiments as models for instrument development studies. Preliminary results show that existing theoretical models for chemistry in Titan's atmosphere cannot adequetely explain the presence and abundance of all trace gases observed in these experiments.

Description: Recent atmospheric calculation suggest that the prebiological atmosphere was most probably composed of nitrogen, carbon dioxide, and water vapor, resulting from volatile outgassing, as opposed to the older view of a strongly reducing early atmosphere composed of methane, ammonia, and hydrogen. Photochemical calculations indicate that methane would have been readily destroyed via reaction with the hydroxyl radical produced from water vapor and that ammonia would have been readily lost via photolysis and rainout. The rapid loss of methane and ammonia, coupled with the absence of a significant source of these gases, suggest that atmospheric methane and ammonia were very short lived, if they were present at all. An early atmosphere of N2, CO2, and H2O is stable and leads to the chemical production of a number of atmospheric species of biological significance, including oxygen, ozone, carbon monoxide, formaldehyde, and hydrogen cyanide. Using a photochemical model of the early atmosphere, the chemical productionof these species over a wide range of atmospheric parameters were investigated. These calculations indicate that early atmospheric levels of O3 were significantly below the levels needed to provide UV shielding. The fate of volcanically emitted sulfur species, e.g., sulfur dioxide and hydrogen sulfide, was investigated in the early atmosphere to assess their UV shielding properties. The photochemical calculations show that these species were of insufficient levels, due in part to their short photochemical lifetimes, to provide UV shielding.

Description: The study uses an emission line, differential imaging camera built by the Science Operations Branch. This instrument allows photometric data to be obtained over a large area of a comet in a large number of resolution elements. The detector is a 100x100 Reticon array which with interchangeable optics can give resolutions from 2" to 30" over a field of 1' to 15'. The camera through its controlling computer can simultaneously take images in on-line and continuum filters and through computer subtraction and calibration present a photometric image of the comet produced by only the emission of the molecule under study. Initial work has shown two significant problems. First the auxiliary equipment of the telescope has not allowed the unambiguous location of faint comets so that systematic observations could be made, and secondly initial data has not shown much molecular emission from the faint comets which were located. Work last year on a software and hardware display system and this year on additional guide motors on the 36-inch telescope has allowed the differential camera to act as its own finder and guide scope. Comet IRAS was observed in C2 and CO+, as well as an occultation by the comet of SAO029103. The perodic comet Giacobini-Zinner was also observed in C2.

Description: The Voyager 1 and Voyager 2 narrow angle cameras have been imaging Uranus and Neptune (through several filters) from distances of several AU for the past four years. The justification for this is to determine the way in which the albedoes of the two planets vary with angle from the sun. The Voyager 1 spacecraft has already reached a phase angle of approx. 40 deg. for Neptune and approx. 70 deg. for Uranus. The albedo of a gaseous planet depends on the phase angle (angle from the sun through the planet to the observer), the color being observed, and the vertical distribution and nature of aerosols and clouds in the atmosphere of the planet. Since the colors are known and the phase angles, and phase curves will be used to constrain models of the aerosol and cloud structrures of Uranus and Neptune. A knowledge of the way albedo varies with phase angle allows one to compute the total amount of sunlight being absorbed by a planet. With knowledge of the solar flux incident on the planet and knowledge of how much infrared is being emitted by the planet (at least in the direction of the Earth and sun) one can determine a rough extimate of the internal heat source of the planet. Although Jupiter and Saturn have measured internal heat sources of magnitude comparable to their absorbed energy from the sun, preliminary results indicate that Uranus may not have an internal heat and that Neptune if it has one that heat source is small.

Description: The physical properties of asteroids were studied by telescopic observations and laboratory and theoretical work. Spectrophotometry from 0.3 to 1.1 microns and 1.2, 1.6 and 2.2 micron photometry allow spectral-compositional classification of asteroids. Based on laboratory data and telescopic observations, it was found that infrared measurements at 1.2, 1.6 and 2.2 microns provide a relatively rapid and accurate method for the classification of minor planets and are important in comparing asteroids with meteorites. This technique was proven and employed in an expanded survey of Apollo-Amor-Aten and other unusual asteroids recently scanned by IRAS.

Description: During the past year three periodic comets were recovered. They were Tsuchinshan 2, Whipple, and Daniel. Follow up positions on four newly discovered comets appeared on IAU cards: Machholz, Hartley, Maury, and Shoemaker 3. Halley was captured shortly after its 1985 conjunction and a set of exposures in late summer was one of the earliest showing tail development. A variety of interesting asteroids were also captured.

Description: Since 1969 every bright comet was measured which has reached a distance of one astronomical unit from the sun. Observing techniques were developed which make it possible to observe as close as elongation 3 deg., and to find, track and measure comets at all wavelengths in full daylight. Comet Halley was measured on twenty four occasions between December 12, 1985 and March 25, 1986. Clear weather seems to come on holidays, and days on which are observed including Winter Solstice, Christmas, New Years, Valentines day, Super Bowl Sunday and the Vernal Equinox. Halley is observed within hours of perihelion passage.

Description: Near-infrared reflectance spectra 0.6 to 2.5 micrometer were acquired of asteroids 1627 Ivar (Amor), 43 Ariadne, 335 Roberta, 386 Siegena and 695 Bella (3:1 Kirkwood Gap) with the IRTF, Mauna Kea. CCD spectra 0.5-1.0 micrometer were acquired of 1866 Sisyphus (Apollo), 17 Thetis, 695 Bella, 797 Montana, and 877 Walkure (3:1 Kirkwood Gap) using facilities at Cerro Tololo Inter-American Observatory. An upper limit on the production rate of CN in asteroid 3200 Phaeton of 〈 4 x 10 to the 23rd power sec was determined based on photometric measurements at 3871A using facilities at Lowell Observatory. This value is in the range of the lowest production rate measured for a comet, however, it does not constitute a positive detection of CN in this asteroid. A first attempt of look for companion objects or evidence of dust debris associated with this asteroid was made with a CCD camera. Whereas the search extended to 19th magnitude (corresponding to 150m and 330m for albedos of 0.15 and 0.03 respectively), a look close enough to the asteroid was not attained to definitively eliminate the presence of coorbiting dust debris.

Description: Narrowband CCD profiles of C2 and grains in several comets (including P/Halley and P/Giacobini-Zinner) were performed. Rotational light curves were made of Comet P/Arend-Rigaux (visible and infrared) yielding the size, shape, albedo, and rotation period of the nucleus. Production rates were measured as a function of heliocentric distance for OH, CN, and C2 in P/Giacobini-Zinner and for OH, NH, CN, C3, and C2 in P/Halley. Detection and measurement was made of forbidden (O I) lines near 6300 and 5577 A in P/Halley, permitting the production rate of oxygen from CO to be distinguished from that from H2O. Identification of C-12C-13 lines in cometary spectra indicating a possible enrichment of C-13 over the telluric value was made. An assessment of techniques for detecting (determining the existence of) a trans-Neptunian comet belt is included.

Description: The Voyager data in a newly produced noise-reduced and recalibrated format has been received. New color spectrograms were developed on high resolution color terminals which display this data. The production of these new spectrograms utilizing the new format data is quite important, because it eliminates a serious problem of noise contamination and miscalibration in the old data set. In addition, a new Jovian plasma model was introduced, which includes the Io torus and accounts for 7 ionic species. The new plasma model is important in the ray tracing of hectometric (HOM) and kilometric (KOM) radiation which may be influenced by the Io torus.

Description: A multi-color, broad-band photographic program for monitoring atmospheric variability of Jupiter and Saturn with the 61-cm, f/75 telescope was continued. The archivial product consists of approximately 20 sequential images on 3 1/4 x 4 1/4 glass plates with a plate scale of 4.53 arc sec/mm. An eleven-step sensitometric wedge, recorded times of acquisition, and fiducial marks which determine the orientation of the plate, are recorded on each individual plate. This allows accurate positional measurements, as well as detailed relative surface brightness determinations. Detailed measurements of the Red Spot are being utilized in a study of zonal velocity variation and the ability to predict the longitude of the Red Spot during the Galileo mission. An ongoing 5-color series of Saturn has been maintained to map the seasonal changes in the belt-zone reflectivity. Digitization of a series of blue images containing the Red Spot and a series of red and blue images excluding the Red Spot are being processed and reduced to normalized surface brightness maps. This data is being utilized to map time-dependent brightness variations of selected features, belts, and ones.

Description: The interior structure of the Jovian planets was studied by means of observational data obtained by ground-based astronomy. Recent work was oriented toward a determination of oblateness from occultation measurements of the shape of planetary atmospheres. This provides a determination of the degree of central condensation of the planet, which is then compared with interior models and theoretical equations of state. As a serendipitous result of the attempts to measure the oblateness of Neptune, a partial Neptune ring (or arc) was discovered following an occultation observation on July 22, 1984. During 1985, older observations were reexamined to determine whether Neptune arcs had been detected (but not identified) during previous occultations. It appears that Neptunian arcs may locally imitate Uranian rings, with an 1981 event resembling Uranus' epsilon ring, while an 1984 event was more similar to the thinner Uranian rings such as the alpha ring.

Description: This program supports NASA's deep space exploration missions, particularly those to the outer Solar System, and also NASA's Earth-orbital astronomy missions, using ground-based observations, primarily with the NASA IRTF at Mauna Kea, Hawaii, and also with such instruments as the Kitt Peak 4 meter Mayall telescope and the NRAO VLA facility in Socorro, New Mexico. An important component of the program is the physical interpretation of the observations. There were two major scientific discoveries resulting from 8 micrometer observations of Jupiter. The first is that at that wavelength there are two spots, one near each magnetic pole, which are typically the brightest and therefore warmest places on the planet. The effect is clearly due to precipitating high energy magnetospheric particles. A second ground-based discovery is that in 1985, Jupiter exhibited low latitude (+ or - 18 deg.) stratospheric wave structure.

Description: Determination of the size, shape, mean density, and albedo of Ceres was made. Predictions for 133 occultations of bright stars occurring in 1986 and 1987 were completed and published, as have predictions of occultations of stars by Comet Halley. Twenty-nine mutual events involving Galilean satellites were observed at Flagstaff in 1985.

Description: The research effort was concentrated toward comet P/Halley, although observations of other comets including Giacobini-Zinner, Hartley-Good and Thiele were made as opportunities arise. In preparing for the apparition of P/Halley, detailed predictions for the emission in the 18 cm OH transitions were made in order to assist observers and to indicate what type of data would be particularly valuable. Likewise, since occultations by the comet of background radio sources can provide unique types of information, the tracks of P/Halley and P/Giacobini-Zinner were surveyed with the NRAO Very Large Array, background sources were mapped, and a catalogue of occulted sources published. Beginning in September, 1985, regular observations of the 18 cm OH lines have been made for P/Halley using the 43 m antenna of the NRAO in Greenbank, West Virginia. These data promise to provide the most accurate time sequence for the OH emission for any comet ever obtained at radio wavelengths. From the linewidth and shape, information is obtained on the kinetics of the gas in the cometary coma. An extensive series of observations have been undertaken with 14 m antenna to study emission from the HCN molecule in P/Halley. These data provide the first definitive detection of this component of the cometary ices. Interesting variations in the production of HCN were observed with time scales less than a day. Likewise, there appeared to be variations in the ratio of the hyperfine components of the J = 1-0 transition.

Description: Work completed on Apollo 14 basalts has been published. The two dates obtained from these rocks comprised the oldest and two of the three oldest ages (4.1 and 4.3 billion years) known for lunar maria basalts; thus their ages are important in understanding the moon's earliest history. Owing to the antiquity of these rocks, two more fragments have been dated as part of a second ASEE/NASA SFF program. The new ages are 3.95 and 4.12 billion years, thus further establishing and amplifying the earlier results. This work, although perhaps more interesting for its chronologic information, was begun as a test of chemical and petrographic models. Fragments of Apollo basalt were placed into five categories, based on petrologic and chemical, especially rare-earth element, composition. Isotopic studies were begun in an attempt to determine if the five groups of basalts were related by age or initial isotopic composition (isotopic composition of lava at time of extrusion). Although a few of the representatives of the five groups have the same age and/or initial strontium-isotopic composition, within the analtytical uncertainties, most apparently are unrelated. Petrologic implications of these data will be published in an appropriate journal.

Description: The carbon isotopic composition of individual organic compounds of meteoritic origin remains unknown, as most reported carbon isotopic ratios are for bulk carbon or solvent extractable fractions. The researchers managed to determine the carbon isotopic ratios for individual hydrocarbons and monocarboxylic acids isolated from a Murchison sample by a freeze-thaw-ultrasonication technique. The abundances of monocarboxylic acids and saturated hydrocarbons decreased with increasing carbon number and the acids are more abundant than the hydrocarbon with the same carbon number. For both classes of compounds, the C-13 to C-12 ratios decreased with increasing carbon number in a roughly parallel manner, and each carboxylic acid exhibits a higher isotopic number than the hydrocarbon containing the same number of carbon atoms. These trends are consistent with a kinetically controlled synthesis of higher homologues for lower ones.

Description: One aspect of the study of Titan's atmosphere is the elucidation of the chemical and physical nature of the aerosols. In order to facilitate this, a program to produce laboratory synthesized model materials for Titan's aerosol and to study their chemical and physical properties is now in progress. Various processes, including electric discharge, photolysis by ultraviolet light, and irradiation by energetic particles, will be used to produce the materials. A first set of experiments where a nominal Titan mixture (97%N2, 3% CH4, 0.2% H2) was subjected to pulsed high temperature shocks yielded a reddish brown waxy solid. This material was subjected to pyrolysis/gas chromatography, a technique that has been proposed as a method for analysis of the Titan aerosols. Preliminary results show the material to consist of simple hydrocarbons but little else, at least up to temperatures of 600 C. Since the material was colored, compounds other than those mentioned above must be present.

Description: The ROCOZ-A radiometer measures ozone by long pathlength photometry in the stratosphere and lower mesosphere. After a rocket launch to an apogee of 70 km, the instrument measures the solar ultraviolet irradiance over its four filter wavelengths as it descends on a parachute. The fundamental values from ROCOZ-A are ozone overburdens versus radar altitude from 53 to 20 km. The slope of these values gives ozone number density. At one standard deviation the repeatability of the ozone overburden measurements averages 2.4 percent. For ozone number density the repeatability averages 3.2 percent with a significant increase at altitudes below the ozone number density maximum. The accuracy limits for overburden and number density are estimated at 5-7 percent. With auxiliary measurements of pressure and temperature, ozone results are also produced in terms of ozone mixing ratio, albeit with a slight broadening of the estimated accuracy limits. The vertical response of ROCOZ-A ozone measurements (full width at half maximum) is 4 km. The assembly of ROCOZ-A profiles can be used to compare with measurements from each of the current NASA and NOAA satellite ozone instruments. In addition, the repeatability of ROCOZ-A allows the use of this instrument as a transfer standard between satellite instruments with different fundamental ozone measurements.

Description: The spatial and temporal characteristics of ozone density measured from the SBUV (Solar Backscatter Ultraviolet) spectrometer on Nimbus-7 and the UV and the UV and the IR spectrometers on SME (Solar Mesosphere Explorer) are compared in the altitude region near 50 km where the three data sets overlap. Their temporal characteristics, when averaged over the same longitude range, are remarkably similar with respect to seasonal variations and short term fluctuations induced by transient planetary waves. The long term trends in the three data sets, however, differ significantly with each other. Over the three year period after 1982 ozone mixing ratio at 1 mb decreased by about 10 percent based on SEUV measurements but increased by 12 and 30 percent respectively based on SME-IR and SME-UV measurements. None of these estimates are consistent with the predicted decrease of about 2 percent based on solar UV flux and temperature changes during this period.

Description: The phase diagram of FeO has been experimentally determined to pressures of 155 GPa and temperatures of 4000 K using shock-wave and diamond-cell techniques. A metallic phase of FeO is observed at pressures greater than 70 GPa and temperatures exceeding 1000 K. The metallization of FeO at high pressures implies that oxygen can be present as the light alloying element of the earth's outer core, in accord with the geochemical predictions of Ringwood (1977 and 1979). The high pressures necessary for this metallization suggest that the core has acquired its composition well after the initial stages of the earth's accretion. Direct experimental observations at elevated pressures and temperatures indicate that core-forming alloy can react chemically with oxides such as those forming the mantle. The core and mantle may never have reached complete chemical equilibrium, however. If this is the case, the core-mantle boundary is likely to be a zone of active chemical reactions.

Description: Equivalent width data from Copernicus and IUE appear to have an exponential, rather than a Gaussian distribution of errors. This is probably because there is one dominant source of error: the assignment of the background continuum shape. The maximum likelihood method of parameter estimation is presented for the case of exponential statistics, in enough generality for application to many problems. The method is applied to global fitting of Si II, Fe II, and Mn II oscillator strengths and interstellar gas parameters along many lines of sight. The new values agree in general with previous determinations but are usually much more tightly constrained. Finally, it is shown that care must be taken in deriving acceptable regions of parameter space because the probability contours are not generally ellipses whose axes are parallel to the coordinate axes.

Description: The 12 m telescope of the National Radio Astronomy Observatory has been used at the J = 2-1 transition of CO to increase the known list of giant and supergiant stars with observable circumstellar envelopes. The candidate objects were generally M-type giants and supergiants, chosen for their strong infrared luminosities. Of the 35 objects which were previously undetected, or only marginally detected, 10 were found to produce detectable CO emission. Physical parameters of the envelopes are derived by source modeling. Mass-loss rates vary from 10 to the -7th to 4 x 10 to the -5th solar mass/yr.

Description: Ten fast X-ray transient sources were discovered in the first complete pass of the sky by the HEAO A-1 Sky Survey Experiment, including 7 relatively faint sources and 3 bright ones. The survey technique and each of the transients are described. Four of the transients are identified with active coronal sources; the remaining ones are unidentified. The statistical properties of the total sample of 10 sources are discussed, including event rates, distribution on the sky, and the number-flux distribution.

Description: Techniques are described for accounting for relativistic effects in the analysis of pulsar signals. Design features of instrumentation used to achieve millisecond accuracy in the signal measurements are discussed. The accuracy of the data permits modeling the pulsar physical characteristics from the natural glitches in the emissions. Relativistic corrections are defined for adjusting for differences between the pulsar motion in its spacetime coordinate system relative to the terrestrial coordinate system, the earth's motion, and the gravitational potentials of solar system bodies. Modifications of the model to allow for a binary pulsar system are outlined, including treatment of the system as a point mass. Finally, a quadrupole model is presented for gravitational radiation and techniques are defined for using pulsars in the search for gravitational waves.

Description: In a class of grand unified theories containing SO(10), cosmologically significant axion and neutrino energy densities are obtainable naturally. To obtain large scale structure, both components of dark matter are considered to exist with comparable energy densities. To obtain large scale structure, inflationary and non-inflationary scenarios are considered, as well as scenarios with and without vacuum strings. It is shown that inflation may be compatible with recent observations of the mass density within galaxy clusters and superclusters, especially if strings are present.

Description: The existence of global exponential instability leading to chaos in plane (nonrigid) motions of the three-body system is demonstrated. In the presence of Newtonian attracting forces the trajectories of the three-body system in the configuration space will no longer be geodesic, and their convergence will depend on the geodesic curvature in addition to the Gaussian curvature. It is noted that the global exponential instability occurs in the n-body problem for n greater than 3 if at least two angular coordinates are disturbed, and that the chaotic instability is not necessarily accompanied by an exponential increase of the distance between the mass-points, but is associated with the exponential divergence of trajectories in the configuration space.

Description: A method for calculating mean square velocity fluctuations, mean square temperature fluctuations, and convective flux for a turbulent rotating fluid with externally applied magnetic field is presented. A new spectral model of large scale turbulence is used which requires, as the sole ingredient, the growth rate of the instability generating the turbulence. Results are presented for the convective flux with rotation and magnetic field for a range of parameters of astrophysical interest. This new formula presented here can be viewed as an extension of the mixing length theory to include magnetic fields and rotation.

Description: Isotopic abundance ratios for mercury were determined by mass spectrometry in six samples of bulk material and in one sample of chondrules from the Allende meteorite. A primary purpose of the work was to attempt to verify the anomalous ratios reported for Hg-196/Hg-202 by neutron activation. Measurements were made on the mercury released at temperatures of 250, 450, 600 C, and in some cases, higher temperatures. The precision of the measurements was such that if an anomaly of the magnitude reported exists, it should have been seen. The isotopic abundance ratios for the other mercury isotopes were also measured. Within the errors of measurement these agreed with normal terrestrial values.

Description: A number of extensive linear constructional features occur on the north and east flanks of Alba Patera. They are found in a 150-km-wide zone and comprise aligned ridge elements that are locally associated with short volcanic flows. They are among the youngest volcanic features in the region and are believed to be Martian analogs of terrestrial spatter ridges. On the basis of measurements made on Viking images, it appears that active volcanic fissures on Mars were larger than their terrestrial counterparts.

Description: The shock-implantation of gases is studied by artificially shocking whole rock and power samples of terrestrial basalt to pressures of 2-40 GPa. Ar, Kr, Xe, and Ne were implanted into the silicate. It is observed that the amount of implanted gas is linearly proportional to its partial pressure over a pressure range of 0.0001 to 0.1 atmosphere. The fractionation effect in the implanted gas and the gas diffusion properties are examined. The amounts of gas that would have been implanted with 100 percent efficiency are calculated from the measured porosities of the power samples and are compared to observed abundances. It is determined that the implantation efficiencies are approximately 0.5 percent at 2 GPa, 7 percent at 5 GPa, and greater than 50 percent at both 20 and 35 GPa. The experimental data correlate with the shock implantation of Martian gases without mass fractionation into the shock-melted phase of meteorite EETA 79001.

Description: Abundances of major and trace elements and magnetic properties of 50 impact melt splashes (IMSs) from the Apollo 16 landing site are analzyed to determine the composition of their meteoritic component. MgO-Sc and Ca-Sc variation diagrams and least-squares mixing models are utilized to analyze the IMS, soil, and rock data. Consideration is given to progenitor lithologies of the IMS, the number of impact events represented by the IMS, and the heterogeneity of impact melts from single events. It is observed that the IMSs are composed of either a mixture of anorthosite and low-Sc impact melt rocks or anorthositic norite. It is determined that the surface Cayley layer is composed of TiO2, MgO, Sc, and La concentrations of 0.69, and 7.1 wt pct and 10.5 and 21.2 microg/g, respectively and 0.38 and 5.9 wt pct and 6.1 and 11.8 microg/g, respectively, for the subsurface Cayley layer. The Descartes Formation composition is estimated as TiO2, MgO, Sc, and La concentrations of 0.25, and 3.5 wt pct and 7.7 and 2.2 microg/g, respectively.

Description: Petrographic and major-element analyses are applied to 50 Apollo 16 impact-melt splash (IMS) samples in order to determine their origin and assess the nature of the subregolith source. The macroscopic analyses reveal that the IMSs exhibit a glassy appearance, but the textures range from holohyaline to hyalopilitic. Schlieren-rich glasses dominate the holohyaline areas, and the crystalline areas are mainly spherulitic. It is observed that most IMSs contain feldspathic monomineralic and lithic clasts and no regolithic materials. It is detected that the chemistry of most IMSs is not like the local regolith and appears to represent varied mixtures of VHA impact-melt breccias and anorthosite; the host rocks are mainly dimict breccias. It is concluded that the Cayley Formation is a polymict deposit composed of VHA impact-melt breccias and anorthosites. Tables revealing the macroscopic characteristics of the IMSs and the major-element composition of IMSs and various host rock are presented.

Description: Evidence was recently presented that in medieval times Sirius was a bright red star, rather than the present bluish-white star. Here, the results of attempts to detect possible planetary nebula ejecta toward Sirius using data obtained by the IUE are presented. Based on these results and in the light of recent advances in understanding white-dwarf evolution, it is proposed that Sirius B underwent a recent thermonuclear runaway event triggered by a diffusion-induced CN reaction.

Description: It is shown here that an elevated rate of star formation may be responsible for burning out protogalaxies in the densest galaxy clusters, leading to the formation of candidate gravitational lenses and to an enhanced probability of close association of quasars in regions of apparently low galaxy density. Extreme tidal interactions occurring during the initial collapse of such clusters would stimulate the star formation and also could drive molecular clouds and stars onto radial orbits, fuelling massive black holes and leading to an enhanced frequency of occurrence of quasar pairs. It is argued that a fundamental bias exists against detecting luminous matter in the great galactic clusters.

Description: An investigation of the variable source Circinus X-1 is reported that reveals that this eccentric double-star system is embedded in a nebula of steady radio emission extending over several parsecs, orders of magnitude larger than the binary stellar system responsible for the fluctuating component of emission. This is in marked constrast to most X-ray binaries, where an envelope of radio emission in conspicuously absent. There are difficulties in explaining the emission, but analogies with SS433 and the Crab nebula suggest possible models.

Description: A method for calculating the photodissociation rates needed for photochemical modeling of the stratosphere, which includes the effects of molecular scattering, is described. The procedure is based on Sokolov's method of averaging functional correction. The radiation model and approximations used to calculate the radiation field are examined. The approximated diffuse fields and photolysis rates are compared with exact data. It is observed that the approximate solutions differ from the exact result by 10 percent or less at altitudes above 15 km; the photolysis rates differ from the exact rates by less than 5 percent for altitudes above 10 km and all zenith angles, and by less than 1 percent for altitudes above 15 km.

Description: Data from the BOIC which consisted of three balloon missions conducted in Palestine, Texas from June 1983 to March 1984 are presented. The BOIC was to assess the ability to perform ozone measurements from balloon platforms. The accuracy and precision of the various ozone measurement systems, which were composed of a photometer, a mass spectrometer, and solar UV absorption sensors, are evaluated. The ozone observations obtained with the instruments on the three flight missions are analyzed and intercompared. The flight in situ data are also compared to the National Bureau of Standards reference photometer, satellite measurements, and under simulated stratospheric pressure and ozone concentrations.

Description: An analysis procedure has been developed for derivation of information about the photochemical behavior of ozone near 1 mbar by explicitly accounting for the dynamical transport terms in the continuity equation for perturbations from the zonal mean. The procedure is shown to be valid using data from a numerical transport model and is then applied to LIMS ozone and temperature data, using geostrophic winds to estimate the transport terms. The data study is restricted to March at 2, 1, and 0.7 mbar. Because the temperature deviations are dynamically produced, large temperature deviations are associated with significant ozone transport terms. The anticorrelation between the deviations of ozone and temperature disappears when the transport terms are small. The derived photochemical information is compared to photochemical theory. Although there is overall agreement in the magnitude as well as the latitude, altitude, and time dependencies, discrepancies are suggested which may be related to the long-standing failure of photochemical models to calculate ozone accurately near 1 mbar. The theory suggests that the addition of Cl(x) to the stratosphere will affect the relationship of ozone and temperature at 2 and 1 mbar. Comparison of the photochemical information derived from future ozone and temperature measurements with the results of the present analysis should provide a critical test of the photochemical scheme thought to describe the behavior of odd chlorine in the stratosphere.

Description: A detailed statistical analysis of monthly averages of ozonesond readings is performed to assess trends in ozone in the troposphere and the lower to midstratosphere. Regression time series models, which include seasonal and trend factors, are estimated for 13 stations located mainly in the midlatitudes of the Northern Hemisphere. At each station, trend estimates are calculated for 14 'fractional' Umkehr layers covering the altitude range from 0 to 33 km. For the 1970-1982 period, the main findings indicate an overall negative trend in ozonesonde data in the lower stratosphere (15-21 km) of about -0.5 percent per year, and some evidence of a positive trend in the troposphere (0-5 km) of about 0.8 percent per year. An in-depth sensitivity study of the trend estimates is performed with respect to various correction procedures used to normalize ozonesonde readings to Dobson total ozone measurements. The main results indicate that the negative trend findings in the 15- to 21-km altitude region are robust to the normalization procedures considered.

Description: Twenty-one lunar craters have radar bright ring appearances which are analogous to eleven complete ring features in the earth-based 12.5 cm observations of Venus. Radar ring diameters and widths for the lunar and Venusian features overlap for sizes from 45 to 100 km. Radar bright areas for the lunar craters are associated with the slopes of the inner and outer rim walls, while level crater floors and level ejecta fields beyond the raised portion of the rim have average radar backscatter. It is proposed that the radar bright areas of the Venusian rings are also associated with the slopes on the rims of craters. The lunar craters have evolved to radar bright rings via mass wasting of crater rim walls and via post-impact flooding of crater floors. Aeolian deposits of fine-grained material on Venusian crater floors may produce radar scattering effects similar to lunar crater floor flooding. These Venusian aeolian deposits may preferentially cover blocky crater floors producing a radar bright ring appearance. It is proposed that the Venusian features with complete bright ring appearances and sizes less than 100 km are impact craters. They have the same sizes as lunar craters and could have evolved to radar bright rings via analogous surface processes.

Description: The production of clay mineraloids (CMs) in the weathering of stony meteorites recovered in the Allan Hills and Elephant Moraine areas of Antarctica is investigated, applying electron microbeam analysis, pyrolysis/mass spectroscopy, X-ray diffractometry, and differential scanning calorimetry to whole-rock chips from two eucrites, two diogenites, and an H5 chondrite. The data are presented in tables, graphs, and photomicrographs and characterized in detail. Massive to incipient-vermicular CM formations with smectitelike or micalike compositions and indications of poor crystallization are observed and attributed to hydrocryogenic diagenesis (with little or no liquid water) on time scales of 10-1000 kyr. The need to take the compositional effects of weathering into account before attempting to reconstruct the preterrestrial histories of meteorites is stressed.

Description: Recent ground-based infrared solar spectra at 0.02 per cm resolution in the 3000 per cm region have been analyzed for the atmospheric content of HCl. Nonlinear spectral least-squares fitting applied to spectra obtained at several zenith angles shows little sensitivity of the results to tropospheric HCl but provides an accurate measurement of the total column amount.

Description: Of the four classical novae presently identified as having accurately known optical positions with counterparts in the IRAS Point Source Catalog, two correspond to events observed by IRAS within one year of their respective optical maxima; these are noted to be the first classical novae detected at IR wavelengths longer than 20 microns. The novae are Sgr 1982, Mus 1983, FH Ser (1970) and HR Del (1967), of which the latter two were also detected by IRAS. Mus 1983 is noted to have IR emission characteristics that are consistent with a free-free spectrum, as opposed to dust emission. The behavior of this and the Sgr 1982 nova is consistent with a previously suggested correlation between the inferred mass of heated dust and luminosity/speed class.

Description: This review presents a summary of past work on the ISEE-3 distant tail magnetic field observations. An attempt has been made to bring the many results together as a coherent whole, in the hope that the reader can envision the direction of future research necessary to achieve an understanding of the dynamics of the magnetotail from 60 to 240 earth radii and perhaps beyond.

Description: Theoretical line profiles are presented that demonstrate why 100,000 spectral resolution and high S/N are needed to derive accurate column densities from spectral lines that lie close to the flat part of the curve of growth and may contain multiple velocity components. The aim of the Space Telescope high-resolution-spectrograph observing program is to obtain column densities in the hydrogen and deuterium Lyman alpha lines along a variety of lines of sight within and extending beyond the local cloudlet, in which the sun is located near an edge. The broad chromospheric Lyman alpha emission lines of late-type stars are used as background sources against which to measure the interstellar absorption features. Profiles of interstellar absorption features in Mg II and Fe II lines will be obtained to derive the broadening parameter and/or identify possible multiple velocity components in the lines of sight.

Description: Small-aperture, high-dispersion IUE spectra have been obtained of seven late-type stars that, in general, confirm previous Copernicus results concerning the distribution of hydrogen and deuterium in the local interstellar medium. In addition, the IUE Ly Alpha spectra of Altair, and of the Alpha Cen components, suggest that multiple velocity components exist in these two directions.

Description: The NASA Deep Space Network, a precision telecommunications and radio navigation facility, is described in detail. The first spacecraft relativity test with Mariner 6 and Mariner 7 at solar conjunction is discussed as well as more accurate tests using the Mariner 9 anchored to Mars. Consideration is also given to solar system tests of relativistic celestial mechanics and future prospects. It is noted that the NASA Mars Observer orbital mission is under development and is expected to reach Mars in 1991.

Description: Recent measurements in the IR of the energy emitted by Io suggest that if the observed emission is due to tidal dissipation in Io, then one should observe a very large secular acceleration of Io in its orbit. The purpose of this paper is to investigate the observational evidence which might be examined to verify that hypothesis. The authors have assembled the largest collection of eclipse observations extant and investigated the possibility of observing secular drifts in the period of Io. Preliminary results suggest that large tidal accelerations of Jupiter's satellites do not exist at the suggested magnitude and hence the heat flux measurements probably represent an episodic occurrence.

Description: Relativistic and lunar perturbations must be included in a realistic theory of the secular evolution of planetary elements. The proposed general theory includes the first order of these perturbations. Comparison with more elaborated studies shows that it is sufficient with respect to the accuracy of the present theory.

Description: Recent advances in infrared speckle interferometry reported by Ridgway, et al. (1986) have made possible the determination of the temperatures at the inner radius of certain dusty outflows. When combined with recent data on the thermal annealing and hydrous alteration rates of amorphous magnesium silicate grains, this information allows one to predict that grains heated to high temperatures around stars such as NML Cygnus will be more crystalline than will cooler grains around stars like IRC +10420. In 1985, Jura and Morris (1985) showed that water vapor can condense on previously nucleated refractory grains in some stellar outflows. Stochastic heating events might provide sufficient energy to produce hydrated silicates from orginally amorphous grains provided that the loss of water from such materials does not occur too rapidly. Observable consequences of both types of grain processing are discussed.

Description: Optical and near-infrared observations of comets are combined in a systematic study of the wavelength dependence of the scattering from cometary grains. The normalized rate of change of the reflectivity of cometary grains with respect to the wavelength of observations decreases as the wavelength increases. The observed wavelength dependence of the reflectivity gradient is consistent with an origin by scattering from micron-sized or larger, slightly absorbing spheres. The optically important comet grains are about an order of magnitude larger than the optically important interstellar grains. This size difference is a probable result of grain growth in the cloud from which the comets condensed. Grain properties differ so widely among the comets that any phase angle or heliocentric distance dependences of the continuum color are hidden.

Description: IRAS observations of the extreme hydrogen-deficient supergiant R CrB are presented and discussed. The star is surrounded by an enormous cool dust cloud which is tentatively identified as a fossil remnant of the hydrogen-rich envelope of the star. The angular extent of the emission corresponds to a linear extent of 8 pc, 20 times larger than the largest previously known shell around a late-type star. The radiating material is distributed very symmetrically over a wide range of radial distances from the star. The dust temperature is nearly constant throughout the extended shell. The total mass in the shell is about 0.3 solar mass. The ejection process appears to have occurred in a spherically symmetric fashion with a nearly constant mass loss rate and expansion velocity over a period of about 150,000 yr, terminating about 26,000 yr ago.

Description: In situ nightside electric field observations from the Pioneer Venus Orbiter have been interpreted as evidence of extensive lightning in the lower atmosphere of Venus. The scenario, including proposed evidence of clustering of lightning over surface highland regions, has encouraged the acceptance of currently active volcanic output as part of several investigations of the dynamics and chemistry of the atmosphere and the geology of the planet. However, the correlation between the 100-hertz electric field events attributed to lightning and nightside ionization troughs resulting from the interaction of the solar wind with the ionosphere indicates that the noise results from locally generated plasma instabilities and not from any behavior of the lower atmosphere. Furthemore, analysis of the spatial distribution of the noise shows that it is not clustered over highland topography, but rather occurs at random throughout the latitude and longitude regions sampled by the orbiter during the first 5 years of operation, from 1978 to 1984. Thus the electric field observations do not identify lightning and do not provide a basis for inferring the presence of currently active volcanic output. In the absence of known evidence to the contrary, it appears that Venus is no longer active.

Description: Satellites smaller than Mimas (r = 195 km) are distinguished by irregular overall shapes and by rough limb topography. Material properties and impact cratering dominate the shaping of these objects. Long fragmentation histories can produce a variety of internal structures, but so far there is no direct evidence that any small satellite is an equilibrium ellipsoid made up of noncohesive gravitationally bound rubble. One many bodies that orbit close to their primary the tidal and rotational components of surface gravity strongly affect the directions of local g and thereby affect the redistribution of regolith by mass wasting. Downslope movement of regolith is extensive on Deimos, and is probably effective on many other small satellites. It is shown that in some cases observed patterns of downslope mass wasting cold produce useful constraints on the satellite's mean density. The diversity of features seen in the few high-resolution images of small satellites currently available suggests that these objects have undergone complex histories of cratering, fragmentation, and regolith evolution.

Description: The orbital properties, surface compositions, opposition surges, masses, radii, and densities of the satellites of Uranus are presented. It is noted that the Uranian satellites are comparable in size to the largest of Saturn's icy satellites while density measurements suggest that the bulk compositions of Ariel and Umbriel might be different from those of Titania and Oberon. Consideration is given to the two satellites of Neptune and the question of a third satellite is addressed. The elements of Charon, determined from astrometric observations by photographic and speckle interferometric techniques, and then from eclipse observations, are given. The diurnal period of Pluto and its photometric lightcurve are discussed. The similarities and differences existing between the satellites of Uranus and Neptune and the Pluto-Charon pair are mentioned briefly.

Description: When natural satellites and ring particles are embedded within magnetospheric plasmas, the charged particles interact with the surfaces of these solid bodies. These interactions have important implications for the surface, the atmosphere of the parent body, and the magnetosphere as a whole. Significant erosion of the surface by sputtering, as well as redeposition of sputter ejecta, can occur over geologic time. The surface can also be chemically modified. Sputter ejecta can make important contributions to the atmosphere; sputtering provides a lower limit to the atmospheric column density even for arbitrarily cold satellite surfaces. Sputter ejecta escaping from the parent body can form extensive neutral clouds within the magnetosphere. Ionization and dissociation within these neutral clouds can be dominant sources of low-energy plasma. The importance of these processes is discussed for the satellites and magnetospheres of Jupiter, Saturn and Uranus.

Description: The origin of orbital resonances is shown in the demonstration of the evolution of a pair of planetary satellites through a commensurability of the mean motions by a sequence of diagrams of constant energy curves in a two-dimensional phase space; the closed curve corresponding to the motion in each successive diagram is identified by its adiabatically conserved area. It is found that two-body resonances serve as a basis in the solution of the problem of the origin and evolution of the three-body Laplace resonance among the Galilean satellites of Jupiter. The unusual rotation state of Saturn's satellite Hyperion which is expected to tumble chaotically for an indefinite amount of time is discussed.

Description: Four tables of planetary and satellite data are presented which list satellite discoveries, planetary parameters, satellite orbits, and satellite physical properties respectively. A scheme for classifying the satellites is provided and it is noted that most known moons fall into three general classes: regular satellites, collisional shards, and irregular satellites. Satellite processes are outlined with attention given to origins, dynamical and thermal evolution, surface processes, and composition and cratering. Background material is provided for each family of satellites.

Description: Thermal evolution models of satellites are discussed with emphasis placed on the fundamental physical processes common to all planetary bodies. A comparison is made between the different evolutionary tracks followed by individual satellites. Consideration is given to the compositions and structures of satellites, heat sources, relevant thermal and mechanical properties of the materials in satellite interiors, and heat transfer mechanisms. Thermal history scenarios are presented for the majority of the satellites of the solar system and these are related to the constraints imposed by surface geology.

Description: Solar system origin and planetary formation are discussed with emphasis placed on accretion disk dynamics, disk instabilities, giant gaseous protoplanets, condensation, sedimentation, coagulation, planetesimal swarm evolution, giant planet formation, and implications for satellites. Disk formation and the dynamics of a protosatellite disk are considered as well as satellite accretion, impact disruption and ablation, and satellite capture. Possible explanations for each of the satellite systems are offered. It is concluded that satellite formation involves a variety of processes.

Description: Data from long-term pulse-timing observations of Cen X-3 are compiled and analyzed to determine the evolution of the orbital period, and the implications of the results for other massive X-ray binaries are discussed. Third-body effects, tidal effects, and mass-loss/transfer effects are considered as possible causes for the orbital-period decay observed in Cen X-3, and it is concluded that strong tidal coupling between the companion star and the orbital causes the period decay via orbital instability and/or mass loss. Applying these results to the Roche-lobe-overflow models of Savonije (1983), the evolutionary expansion rate of the Cen X-3 companion and the Roche-lobe shrinking rate are estimated as about 2 x 10 to the -7th/yr and about 1 x 10 to the -6th/yr, respectively, implying an X-ray lifetime of about 5000 yr. Estimates of the companion mass-change rate and period decay for Cen X-3 and four other objects are presented in a table.

Description: Ozone measurements from 1970 to 1984 from the Nimbus 4 backscattered ultraviolet and the Nimbus 7 solar backscattered ultraviolet spectrometers show significant decrease in total ozone only after 1979. The downward trend is most apparent in October south of 70 deg S in the longitude zone 0 to 30 deg W where planetary wave activity is weak. Outside this longitude region, the trend in total ozone is much smaller due to strong interannual variability of wave activity. This paper gives a phenomenological description of ozone depletion in the Antarctic region based on vertical advection and transient planetary waves.

Description: A more detailed examination of the TOMS observations reveals a number of important aspects of the Antarctic ozone depletion. First, it is noted that the presence of large scale disturbances around the edge of the ozone hole can lead to highly variable station observations. Second, an examination of the zonal mean total ozone for the seven Octobers shows that the large systematic decline is not simply confined to the polar region but exists at midlatitudes as well. Integrations of the total ozone from the South Pole northwards show that a portion of the systematic trend of decreasing Antarctic total ozone (prior to 1985) seems to be due to a redistribution of total ozone to subpolar and midlatitude regions. That is, decreases at high latitudes are compensated by increases at lower latitudes. The correlation between zonal mean total ozone and 70 mb zonal mean temperatures from polar to midlatitudes shows that the systematic decreases in total ozone is well correlated with a systematic decrease in stratospheric temperatures.

Description: The ozone profiles measured by SBUV in the region of the Antarctic ozone minimum are in error as archived for altitudes below the 7 mb level in the atmosphere because of the lack of a reasonable climatology to use for the initial guess profile. The ozone profile error in this region is examined, and it is shown that use of a reasonable climatology in this unusual region results in ozone profiles that agree substantially better with the balloon observations available from the Syowa station. The corrected profiles show that by 1984 there was 35 percent less ozone in the 15 to 30 km region than in 1979, and 14 percent less even in the 40 to 50 km region.

Description: The early thermal profiles and the lithospheric stability and strength of Ganymede are quantitatively determined on the basis of brittle lithosphere thickness estimates derived from the width and spacing of extensional tectonic features, together with lithospheric strength envelopes for ice. Plots of the brittle and ductile yield stress vs. depth for the icy lithosphere of Ganymede exhibit a linear increase in brittle strength with depth to a maximum at the brittle-ductile transition that is followed by an exponential decrease in ductile yield stress with depth. The results obtained imply that the thermal gradient and lithospheric strength have varied laterally by factor as great as 5, and that Ganymede underwent cooling in a highly inhomogeneous fashion with lateral thermal anomalies. The present analysis furnishes reasons for the stability of large cratered terrain remnants.

Description: Daytime and nighttime vertical profiles of the tropospheric trace gas N2O were determined from grab sample collections off the Atlantic and Gulf coasts of Florida. The grab samples were collected during the week of October 7-13, 1984, from a Lear jet during descent spirals over an altitude range of 12.5-0.3 km in approximately 1.2-km intervals. During this period there were two distinct airflow regimes sampled: (1) the surface boundary layer (less than 2 km), in which the wind direction was typically easterly; and (2) the regime above the boundary layer, which was predominantly characterized by westerly flow. N2O mixing ratios, normalized to dry air, were determined from 148 daytime and nighttime samplings. N2O was found to be uniformly mixed at all altitudes at 301.9 + or - 2.4 parts per billion by volume.

Description: Thermal-infrared and visual images obtained simultaneously of comet Giacobini-Zinner on UT 1985 August 4.4 are presented. The 10.8-micron map, which spans several arc minutes with 8-arcsec resolution, is the first ground-based infrared image of a comet. Considerable spatial structure is evident in the map, including a curved dust tail consisting primarily of dust grains larger than 100 microns. The width of this large-grain tail implies that these grains depart the nucleus with velocities less than 3 m/s. The distribution of grain albedo is determined for the central 1 arcmin. It is speculated that an observed increase in the albedo by a factor of 2 with distance from the nucleus and prolonged radius vector results from the confinement to the orbital plane of large fluffy grains previously considered for GZ by others; the lower albedo of this dust could result from multiple internal scattering increasing the probability of absorption of incident light. It is estimated that dust was departing the nucleus at the rate of about 8 x 10 to the 5th g/s, comparable to that derived for many other comets.

Description: A number of type 1.8 and 1.9 Seyfert galaxies have been observed at the VLA in order to compare their properties with those of the other types of Seyfert galaxy. The observed types have radio luminosities in the range of 10 to the 39th-40.5th args/s, with the median near 10 to the 40th ergs/s. Most of these galaxies have radio sources with diameters of about 500 pc or less. The ratio of radio luminosity to featureless optical continuum luminosity in the Seyfert 1.8/12.9 galaxies and Seyfert 1.2/1.5 galaxies is intermediate between the values for Seyfert 1 and Seyfert 2 galaxies. The infrared-to-radio ratio decreases along the sequence from Seyfert 1 galaxies, through intermediate Seyfert galaxies, to Seyfert 2 galaxies. This systematic statistical difference in the ratio of two aspect-independent quantities implies that the differences among the Seyfert classes cannot be attributed solely to differences in viewing angle.

Description: The development of reconstruction algorithms that correct for diffraction effects in radio occultation measurements is described. The reciprocal Fresnel transform relationship between the complex amplitude of the observed coherent signal and the complex microwave transmittance of the rings is derived using the Huygens-Fresnel formulation of the diffraction problem. The effects of the finite data segment width, the uncertainties in the Fresnel scale, systematic phase errors in the kernel of the inverse transform, reference oscillator instabilities, and random noise measurements on the resolution of the reconstructed transmittance are analyzed. Examples of reconstructed opacity profiles for some regions of Saturn's rings derived by applying the reconstruction theory to Voyager 1 at Saturn data are presented.

Description: Mobile Very Long Base Interferometry (VLBI) and Global Positioning System (GPS) geodetic measurements have many error sources in common. Calibration of the effects of water vapor on signal transmission through the atmosphere, however, remains the primary limitation to the accuracy of vertical crustal motion measurements made by either technique. The two primary methods of water vapor calibration currently in use for mobile VLBI baseline measurements were evaluated: radiometric measurements of the sky brightness near the 22 GHz emission line of free water molecules and surface meteorological measurements used as input to an atmospheric model. Based upon a limited set of 9 baselines, it is shown that calibrating VLBI data with water vapor radiometer measurements provides a significantly better fit to the theoretical decay model than calibrating the same data with surface meteorological measurements. The effect of estimating a systematic error in the surface meteorological calibration is shown to improve the consistency of the vertical baseline components obtained by the two calibration methods. A detailed error model for the vertical baseline components obtained indicates current mobile VLBI technology should allow accuracies of order 3 cm with WVR calibration and 10 cm when surface meteorological calibration is used.

Description: Under the assumption that the cross-equatorial Hadley circulation plays a key role in the onset of Martian global dust storms, numerical simulations indicate that a northern hemisphere dust haze weakens its intensity and, thereby, its contribution to the surface stress in the southern hemisphere. Since this in turn reduces the possibility of global dust storm development, the interannual variability observed is the result of either a competition between circulations in opposite hemispheres, in which case the variability has a random component, or it is the result of dust cycling between hemispheres, so that the variability is related to the characteristics of the global dust storms themselves.

Description: The design features of the Comet Rendezvous Asteroid Flyby (CRAF) version of the Mariner Mark II spacecraft are described, together with the instruments to be carried aboard and the goals of the mission. To minimize the cost, computer-aided design, engineering, and manufacturing will be used, and, where possible, established technologies and off-the- shelf products will be incorporated. Planned for a launch in 1992, the CRAF will rendezvous with the Tempel 2 comet in 1996 and will stick with it through 1999, making studies of plasma in the comet's coma and the comet's dust, gas, and nucleus by means of its penetrator rocket which will pierce the nucleus.

Description: The interaction of the solar wind with planetlike obstacles is examined. The four different types of interactions, and the properties of the planets relative to their roles as obstacles to solar wind flow are discussed. The characteristic features of the magnetosphere of Mercury, Jupiter, Saturn, and the earth are described; particular attention is given to the configuration of the magnetosphere and the factors which control the position and shape of the magnetopause. The role of the magnetic field as it becomes modified in the solar wind interaction with nonmagnetic objects possessing an ionosphere is studied and examples of ionospheric interaction, such as Venusian and Titan interactions, are presented.

Description: Observations of the solar wind close to Jupiter are compared with the decametric radio emission (DAM), using data recorded by Voyager 1 and Voyager 2 during 1979. The Non-Io DAM, recorded by both spacecraft and combined using the superposed epoch technique, is found to correlate with the solar wind density and velocity, as well as with the interplanetary magnetic field (IMF) magnitude. In agreement with earlier work using ground-based observations, there are indications that the Non-Io DAM is somehow associated with magnetic sector structure although the precise details of the relationship are still not known and it is not clear if this is a fundamental effect or some secondary effect of intercorrelation.

Description: Dynamic crystallization experiments in which heterogeneous nucleation is an important variable have been completed on four melts of chondrule composition. Compositions were chosen to best represent chondrules with porphyritic pyroxene and radial pyroxene textures. Experimental results show that heterogeneous nucleation is essential for the formation of porphyritic textures. Without preexisting nuclei, too much supercooling is established before crystallization is initiated and the textures are more likely to be dendritic or radial. In the near total absence of nuclei, radial textures can form at cooling rates as slow as 5 C/hr in this study. By varying the heterogeneous nucleation conditions and having a melt in which the appropriate phases are stable or metastable, analogs to most of the recognized chondrule textures can be produced in a single melt composition.

Description: Techniques employed to map the global distribution of stratospheric aerosols using SAGE II data at four wavelengths (385, 453, 525 and 1020 microns) are described. The methods were devised to integrate the 900 data points scanned by the instrument with account taken of the different times the vertical profiles were obtained. The data have been used to calculate the O3, H2O, NO2 and aerosol optical thicknesses. Sample details of data gathered during April 1985 are discussed, with emphasis on difficulties being encountered in analyzing the differences being observed in the dawn and dusk data.

Description: Data on the characteristics of the stratospheric aerosol as measured with sensors on the SAM II and SAGE I satellites and with ground-based and airborne lidar are discussed. Emphasis is placed on the impact of the El Chichon eruptions. The volcanic cloud was tracked to an altitude of 30 km, and was observed to travel around the earth in 3 weeks. The maximum stratospheric loading is estimated at 12 Mtons, which increased the stratospheric optical depth to 0.15-2.0 at the peak period. The particulate loading was predicted to lower the Northern Hemisphere average temperatures by 0.4-0.5 C in 1984-85.

Description: Alongtrack data collected with the Earth Radiation Budget Experiment (ERBE) scanner instrument were used to study an observed limb-darkening phenomenon. A numerical model developed for the longwave exitance as a function of the SZA has agreed well with ERBE data, indicating that the atmosphere is in adiabatic, rather than radiative, equilibrium. A corrected form of the model has been defined for SZA over 60 deg. The model was used to parameterize diurnal data for the Sahara-Saudi and Australian deserts.

Description: Design features and the performance envelope of the SAGE II stratospheric aerosol monitoring instrument on the Earth Radiation Budget Satellite are described. SAGE II was designed to obtain vertical profiles of stratospheric aerosols, monitor global seasonal changes in aerosols, provide data on stratospheric circulation and the behavior of transient events such as volcanic particulate injections, and to investigate atmospheric chemistry. The mmeasurements are centered on extinctions due to aerosols, NO2, O3 and water vapor.

Description: Instruments on board the (presently two) satellites of the Earth Radiation Budget Experiment (ERBE) are collecting data for determining monthly averaged radiation exitances at the top of the atmosphere (TOA). To achieve the accuracy desired of the mission, radiances at the satellite are first calculated, with allowance made of sensor optical properties and the directionality of the TOA radiation field. The subsatellite surface type is classified to adjust for albedo changes and correction values are added for the types of cloud cover detected.

Description: Early results are reported from measurements of the diurnal variability of total and clear-sky regional radiative parameters by the ERBE instruments on one dedicated satellite and the polar-orbiting NOAA-9 satellite. Attention is focused on November 1984, the first complete data set. The scene is identified in terms of longwave and shortwave radiances (daytime) or longwave radiation (night) and maximum likelihood estimates carried out with the addition of Earth Radiation Budget data from Nimbus-7. Analysis of the first data set revealed significant differences between total and clear-sky albedo. The clear-sky and LRE both reach maximum around noon and minimum values at midnight.

Description: The Earth Radiation Budget Experiment (ERBE) is to be a three-satellite complement, of which two satellites were in orbit as of October 1984. Each satellite carries scanners for earth radiance sensing and one nonscanner for solar constant sensing. Of the four channels for earth scanning, two are dedicated to limb-to-limb observations and two view a swath 1000 km wide. Comparisons are made among the channel readings, thus far producing agreement to within 1 percent. Inversion techniques which are being applied to data gathered by the sensors are checked against equivalent procedures and results with the Nimbus-7 and GOES satellites.

Description: The effects changes in stratospheric ozone concentrations have on photochemical models of the atmosphere are evaluated. The study was spurred by the appearance of excessive stratosphere heating above 40 km in radiative transfer computations. A 20 percent reduction in ozone in the 40-55 m altitude interval would offset the anomalous heating values. Comparisons were made between calculated heating rates and in-situ data that included ozone concentrations. Heating rates decreased 0.4 C/day when clouds were present at the 300 mb level, and increased by 0.3 C/day with clouds at the 80 mb level.

Description: The SAGE II limb-scanning radiometer carried on the Earth Radiation Budget Satellite functions at wavelengths of 0.385, 0.45, 0.525, and 1.02 microns to identify vertical profiles of aerosol density by atmospheric extinction measurements from cloud tops upward. The data are being validated by correlating the satellite data with data gathered with, e.g., lidar, sunphotometer, and dustsonde instruments. Work thus far has shown that the 1 micron measurements from the ground and satellite are highly correlated and are therefore accurate to within measurement uncertainty.

Description: Nimbus-7 wide-FOV irradiance data collected from 1981-1985 are used to evaluate the effects of the El Chichon eruptions of 1982 on the earth radiation budget. The north polar region displayed a maximum response of 20 percent in the winter of 1982-1983, with the variation being most apparent in the near-IR 2.8 micron and 0.2-3.8 microns shortwave bands. The data indicate that the particle size distribution was constant for a year after eruptions.

Description: A scalar-tensor-nonmetric theory of gravity without matter fields is shown to be equivalent to the scalar-tensor-torsion theory proposed by German, the only difference being in the source of the Weyl vector or torsion vector (for equivalently the scalar field) which remains arbitrary in the theory. General extended conformal transformations, which leave the curvature tensor invariant, are presented and their implications for metric-affine theories and scalar-tensor theories are discussed.