Theoretical Studies, Astrophysics, and Cosmology

STOEGER and ARAÚJO (Universidade Federal do Rio de Janeiro) and collaborators and students have completed and published their treatment of constructing solutions to the Einstein field equations with cosmological data functions for dust (pressure-free matter) in observational (past-light-cone-based) coordinates in the case of open and closed (non-flat) Friedmann-Lemaître-Robertson-Walker (FLRW) universes and in perturbed FLRW cases. They published their results for all exact spherically symmetric cases in 1999. Now they are working to complete the solution scheme for the general perturbation case (including non-spherically symmetric perturbations to FLRW) and for cases involving a mixture of dust and a vacuum energy (non-zero cosmological constant). They have made significant progress on both fronts.

STOEGER and RIBEIRO (Physics Institute, Universidade Federal do Rio de Janeiro) have begun some preliminary work on bridging the chasm between theoretical relativistic cosmology and the observational cosmology treatment of data as it applies to FLRW models of the universe. In particular, they are trying to describe mathematically the relationship which obtains between the galaxy luminosity function and relativistic energy-density of the universe at various redshifts. They are also studying how such data, including that pertaining to clusters of galaxies, might eventually be able to be used to constrain both cosmological models and luminosity and number evolution, without assuming that the universe on a particular scale is FLRW. One particular motivation for this work is to determine what is the smallest length scale on which our Universe is approximately FLRW.

ELLIS, MCEWAN, and DUNSBY (Department of Mathematics, University of Cape Town) together with STOEGER have completed and submitted preliminary work on both the dynamics and the horizon growth (causality) of inflationary universes with positive spatial curvature. In such universes the curvature will always dominate at early enough times. This puts limits on the number of inflationary e-foldings that can have occurred, without regard for what may have happened in the Planck era. This also means that causality will almost never connect the entire spatial extent of the universe. Any solution to the horizon problem, it turns out, really must be solved in the Planck era. Inflation merely serves to blow up to a very large scale whatever causally self-connected patch emerges from the Planck era. It does not determine the causal self-connectivity of the original patch, nor how large that patch is. Those characteristics must be determined by quantum-gravity processes in the Planck era itself. STOEGER and the Cape Town group are continuing their investigation of these issues, in particular, by deriving more precise constraints on inflationary effects in these models (e-foldings and horizon sizes). They are doing this by treating carefully the mixed-radiation and vacuum-energy dominated pre-inflationary phase of the universe's evolution, and by determining the effect of Planck era processes on the size and homogeneity of the pre-inflationary patch, according to what quantum cosmologists are discovering.

LISZKA (Swedish Institute of Space Science, Sförs), PACHOLCZYK (Steward Observatory, University of Arizona), and STOEGER are continuing their work on ROSAT and Chandra X-ray data sets of Seyfert galaxies to separate out deterministic signals, which may be due to processes in the sources themselves, from both extrinsic and intrinsic stochastic processes. This work is directed toward a more precise understanding of the central engine of active galactic nuclei, in particular, whether or not there is just a single central black hole or rather multiple black holes (e.g., a cluster of black holes). STOEGER and PACHOLCZYK are also beginning to study how black holes may be involved in gamma-ray bursts, and how initial gamma-ray bursts from ballistic black-hole events can be degraded in some cases to X-ray energies through their interaction with surrounding matter and high energy radiation fields (photon-photon pair-production processes).

JUST (Department of Physics, University of Arizona) continues to work in quantum field theory together with STOEGER, particularly on developing and refining the quantum induction program.

WHITMAN continues to work on the holonomy problem. This seeks to identify the possible geometric structures, one of which being the structure of our universe, that are described by Einsteinian geometry. Within this problem is an older one, first solved around a hundred years ago: the problem of classifying the real, irreducible representations of real forms of the simple complex Lie algebras. Over the century more understanding and sharper results were reported with respect to this problem. However, this literature is diffused throughout many journals and books, and it is difficult to understand the larger picture. Thus WHITMAN is now working to give an exposition of this development from its beginnings in the theory of Lie algebras. He has also presented another exposition of a part of the holonomy problem. Complex representations of simple complex Lie algebras is the basis for the beginning of the solution of this problem. Among these representations appear the rather surprising spin representations. In order to show how these spin representations might have been discovered, WHITMAN prepared a detailed analysis of the isomorphisms of the low dimensional Lie algebras in which these spin representations naturally appear. With this foundation it became much easier to show the structure of these spin representations as coming from certain Clifford algebras. In particular, the surprising difference between the even-dimensional and odd-dimensional spin representation became very clear. This material was assembled into a set of notes by WHITMAN, "Low Dimensional Isomorphisms of Simple Complex Lie Algebras and Spin Representations."

Extragalactic Research

Understanding star formation rates (SFR) is crucial for the comprehension of galaxy formation and evolution. A key question is: How does the distribution of SFR evolve with redshift? To answer this question, other researchers (Madau and collaborators) attempted in 1996 to measure the redshift evolution of the co-moving SFR density. The result is the so-called "Madau plot." However, this plot is influenced by systematic uncertainties in the underlying SFR scales (extinction and incompleteness biases). To address the incompleteness and environmental effects, FUNES along with KENNICUTT (Steward Observatory, University of Arizona), SAKAI (University of California, Los Angeles), and AKIYAMA (University of Arizona) are obtaining H-alpha images to complete a volume-limited survey of integrated SFRs for a complete sample of nearby galaxies within the local 11 megaparsec volume. In order to probe the population of field galaxies, they are compiling and measuring the integrated H-alpha luminosities and SFRs for a complete sample. The data will be used to: (1) construct the local SFR distribution function as a reference for cosmological look-back studies; (2) develop new diagnostic measures of the rate and distribution of star formation in galaxy populations; (3) quantify the role of starbursts in the evolution of low-mass galaxies; (4) quantify the incompleteness biases in star formation surveys; (5) study the environmental dependence of the SFR distribution function; and (6) provide a reference catalog and image database for use by workers in the field. The observations for this program are being obtained with the Vatican Advanced Technology Telescope (VATT) at Mt. Graham, the Steward Observatory 90-inch Bok Telescope at Kitt Peak, and the Cerro Tololo Interamerican Observatory 0.9-m telescope at Cerro Tololo, Chile.

FUNES continues to seek an accurate determination of the black-hole mass in early-type disk galaxies by studying the gaseous kinematics in the inner regions of these galaxies. This work is being done in collaboration with BERTOLA, CORSINI, PIZZELLA (University of Padua, Italy), SARZI (University of Durham. U.K.), and VEGA BELTRAN (Instituto de Astrofisica de Canarias, Canary Islands). It is now commonly accepted that almost every galaxy hosts in its center a supermassive black hole (BH). Supermassive BHs may have played a major role in galaxy evolution, as recently indicated by the correlation between the black-hole mass and the bulge stellar velocity dispersion. However, it should be kept in mind that the current demography of supermassive BHs suffers from important biases related to the limited sampling over the different basic properties of their host galaxies. In particular, it is evident that the number of BH mass estimates in spiral galaxies is strongly under-represented. New spectroscopic observations with the Space Telescope Imaging Spectrograph have been scheduled to map the ionized gas velocity field of three early-type disk galaxies, for which we will be able to derive high precision BH mass measurements. Indeed, the sample galaxies have been selected from among 37 observed objects by means of ground-based, high-resolution spectroscopy, whereby we recognized in the central regions of the selected galaxies the clear presence of a circum-nuclear Keplerian disk of ionized gas suitable for dynamical modeling.

OMIZZOLO and CRISTIANI (European Southern Observatory, Munich) are determining the luminosity function for a sample of about 800 X-ray emitting, bright quasar candidates. Low-resolution red region spectra were obtained in collaboration with CORBALLY at the Steward Observatory Bok Telescope on Kitt Peak, and reduction of the data was completed at the Department of Astronomy of the University of Padua. OMIZZOLO and CRISTIANI are also studying the spectral data for NGC 526, an active galaxy, to determine the kinematics of this interesting object. The spectra were taken at the ESO observatories in Chile and at the Galileo Italian National Telescope in the Canary Islands.

The Galaxy and Galactic Objects

CORBALLY and GRAY (Appalachian State University, Boone, North Carolina) completed their spectroscopic search for lambda Boötis stars among late B, A, and early F-type stars in 12 young and intermediate-age open clusters. Numerous classical Ap (three notably extreme) and Am stars were found among the 130 stars observed. In addition, three emission-line stars and two candidate lambda Boötis stars were found. Neither of these lambda Boötis candidates turned out to be members of their respective clusters. When combined with 184 stars previously classified in 10 other intermediate-age open clusters, also devoid of lambda Boötis stars, and correcting for cluster membership probabilities, a statistically significant null result was obtained. Since the frequency of lambda Boötis stars in the field amounts to 2%, a small but significant percentage, the null result from clusters suggests some factor(s) external to the star and related to membership in open clusters that prevents the operation of the lambda Boötis mechanism.

The investigation of heavily reddened stars in clusters and of peculiar stars continues. These were selected by STRAIZYS (Institute of Theoretical Physics and Astronomy, Vilnius, Lithuania) from photometric classifications in the Vilnius seven-color system. Heavily reddened stars in the area around Nova V1500 Cygni, in the Camelopardalis dark clouds, and in the dark cloud between the North American and Pelican Nebulae have been classified by CORBALLY from spectra he obtained with the Steward Observatory's Bok Telescope.

RUEGER (Diocese of Brooklyn), with the help of RECCA (Manhasset, NY), has finished processing the UBVRI observations obtained with the VATT of two fields in the North Galactic Pole (NGP). With CORBALLY, they are using these fields to calibrate new, direct images of the NGP that were taken with the MDM 1.3-m McGraw-Hill Telescope in the spring. These images, each 45 arcmin square, were acquired through a collaboration with CROTTS (Columbia University), whose MDM 8K CCD array camera was used to considerably enlarge the search area for G-dwarf stars in the Galactic Halo.

CORBALLY, GRAY and McFADDEN (Appalachian State University, Boone, North Carolina), and GARRISON (David Dunlap Observatory, University of Toronto) have been joined by O'DONOGHUE (Vatican Observatory Research Group visiting scholar) this year in their project to obtain spectra, spectral types, and basic parameters of the 3600 stars within 40 parsec of the sun and earlier than M0 spectral type. This is part of the Nearby Stars (NStars)/Space Interferometry Mission Preparatory Science program, and its goals were described in the Annual Report of 2000. Progress has been steady since the project began in July 2000. Some 60% of the spectra have been observed, some 20% have been classified, and the analysis technique was refined for late-type spectra and is being applied down to K5. To help with the analysis, O'DONOGHUE traveled to Appalachian State University in July to work with GRAY. While there, she acquired data that had already been obtained by the project as well as the computer programs GRAY had written for analysis of the spectra. When she arrived at the Vatican Observatory Research Group in September, she brought with her familiarity and experience with the programs, as well as the programs themselves.

In the age of "big glass," the future of smaller telescopes (up to 4-m aperture) might be questioned. At the prompting of OSWALT (Florida Institute of Technology), the general editor of a book on this topic, CORBALLY, GARRISON, and GRAY collaborated in thinking through which spectroscopic observations from smaller telescopes would best provide the high priority projects for stellar physics in the present decade. Various kinds of surveying and monitoring of stars were proposed, along with the refinement of digital and automated techniques in the classification and analysis of stars. In all of the proposed projects, the complementarity between data obtained with small and large telescopes was stressed, since astronomy of the future will require that both kinds of telescopes be used efficiently to understand the most interesting stars.

Stellar population survey work, long a mainstay of astronomy at the Specola, continues today with an innovated combination of electronic data collection and computerized data reduction. A historical perspective of the evolution of this work is found in the "From the Director" section of this Annual Report. At present, the work facing the astronomers is threefold: (1) to understand and learn to correct for all the fluctuations inherent in the electronic gathering of faint light with CCD chips; (2) to collect overlapping data sets that can serve to tie together the existing Strömgren and Vilnius data with the next generation of Stromvil data sets; and (3) to address the need that arises from all these data for a repeatable, automated system where computer analysis of the electronic images can help speed up the enormous work of classifying hundreds of stars in hundreds of CCD images. Work on all three of these issues was carried forward by BOYLE, in collaboration with PHILIP (Union College, Schenectady, New York), JANUSZ (Cracow, Poland), DASGUPTA (Cardiff, Wales), SMRIGLIO (University of Rome), and KAZLAUSKAS, LAUGALYS, and STRAI_YS (Vilnius, Lithuania).

During the course of the year, BOYLE spent 23 days in separate runs at the VATT with PHILIP to obtain images of globular clusters and open clusters with the Stromvil filter system. KAZLAUSKAS and LAUGALYS spent 39 nights observing standard stars at the Mt. Lemmon 60-inch telescope in Tucson and 7 nights at the United States Naval Observatory 1-m telescope in Flagstaff, Arizona. The goal of this work was to calibrate the Stromvil system by taking photoelectric standards in selected fields including open and globular clusters, and also for field stars.

JANUSZ has developed an automated system for data reduction of these CCD images that allows the computer to recall the complex sequence of steps needed to remove known artifacts and errors (flat fielding) from each image, and that can even automatically identify stars of interest within the field. This speeds up the reduction process by a large factor. BOYLE and JANUSZ tested and refined this system, and DASGUPTA then applied it to real-world cases, comparing the reductions done with the automated system with those performed by hand using traditional methods. The final version of this system promises to greatly reduce the time and effort needed to classify stars in a set of CCD images.

The goal of all the work described above remains the classification and characterization of stars in various regions of the galaxy. This stellar census will contribute to our understanding of how the Milky Way galaxy, and other spiral galaxies, develop over time.

IGEA, in collaboration with HUGGINS (Physics Department, New York University) is studying dust scattering in multiple-shell circumstellar envelopes. When a star ejects matter periodically or episodically, it forms a series of nested, concentric shells. Such a phenomenon has been recently observed around a number of asymptotic giant branch (AGB) stars and around some post-AGB stars. It may prove to be an important phenomenon in the later stages of stellar evolution. Radiative transfer of scattered light in spherical geometry is fairly well understood, but little is known about transfer is such multiple-shell envelopes. IGEA and HUGGINS are carrying out Monte-Carlo calculations for dust scattering in such shells, which are illuminated by both external and internal radiation. The principal variables in the calculations to reproduce the observations are the dust grain properties and the shell geometries.

Planetary Sciences

Meteorites

In recent years, CONSOLMAGNO along with STRAIT (Alma College, Michigan) and BLAND (Open University, Milton Keynes, England) have studied microcrack porosity in meteorites, correlating the measured porosity in a hand sample with the amount of volume taken up by cracks in a thin section of the same meteorite. A problem with meteorite thin sections has been that previously only a tiny fraction of an entire section typically was imaged; at times, as few as two images were used to characterize the entire section. This past year, however, the researchers worked with a thin section of Knyahinya (L/LL 5), which fell in Ukraine in 1866, that has been imaged over much of its surface using a JSM 840A SEM at Central Michigan University. Several hundred digital backscatter electron microscope images were generated that covered approximately 50% of the surface. Porosity in the thin section images was measured using NIH Image software. The data, averaged over the areas, indicate an average porosity of 6.0%, with about 0.5% of the cracks filled. This was in agreement with the porosity previously measured by CONSOLMAGNO and BRITT (University of Tennessee) in the whole rock.

In evaluating the porosity distribution in the thin section of the Knyahinya meteorite, the researchers observed that the porosity tended to be higher at the edges of the section, where larger cracks were evident; several areas had significantly higher porosity (10-15%). These areas tend to have major cracks through the fabric of the section, large holes, or gaps at the edges of large inclusions. There was a gradual transition into and out of these high-porosity areas, so it was not an artifact of the measurements. This may be consistent with the idea that these cracks are the result of a shock having passed through the meteorite, with a greater effect near its edges. When did this shock afflict the rock? It could have occurred at any timewhen the rock was residing on its asteroidal parent body; during the event that ejected the rock into Earth-crossing orbit; or even during the shock it experienced when hitting the Earth. Telling the difference will require measuring the microcrack porosity of different types of meteorites, including meteorites that came from rocks known to have been fractured while on the surface of an asteroid and those that appear to have remained relatively intact before arriving at Earth. The one event that all meteorites have in common is their arrival at Earth; if all meteorites show identical microcracks, regardless of type or previous history, that would suggest the cracks were all made at this time, while differences among types would be consistent with cracks occurring in the asteroidal parent body.

In other meteorite-related activities, ROCHETTE (Istituto Nazionale di Geofisica, Rome and University of Aix-Marseille, France) visited the Vatican meteorite collection, housed at the Vatican Observatory's headquarters in Castel Gandolfo, in January to make measurements of the magnetic susceptibility of more than three hundred stony meteorites in the collection. Measurements of the magnetic property of meteorites, which is controlled by their iron content, may provide a rapid nondestructive technique to characterize meteorite samples and probe their homogeneity in the 1 to 100 cc volume ranges. Moreover, the knowledge of average magnetic properties for a given meteorite class is needed to interpret spacecraft magnetic data, such as provided in possible future follow-ons to the NEAR mission to asteroid Eros. Magnetic susceptibility is the most suitable parameter to measure, as it can be measured on various volumes and shapes, and it is also nondestructive of the paleomagnetic natural remnant magnetization. This work was part of a larger effort, involving ROCHETTE, SAGNOTTI (Istituto Nazionale di Geofisica, Rome), FOLCO and MELLINI (Antarctic Museum of Siena, Italy), MARAS and PANZARINO (University of Rome), PESONEN and TERHO (University of Helsinki), and SERRA (Museum of San Giovanni in Persiceto, Italy), to characterize the magnetic properties of meteorites held in collections throughout the Italian peninsula. The researchers merged this database with previous data from Finnish and Czech collections, allowing them to analyze about 750 different ordinary chondrites, including both those seen to fall and collected while still fresh, and those found in places like hot deserts or Antarctica. For a large number of meteorites, especially falls (those recovered after having been observed falling to Earth), numerous samples from various collections were measured, allowing the team to see if the susceptibility values were the same from sample to sample. Falls turn out to be quite homogeneous; finds (meteorites not observed falling to Earth) are less so, as are some brecciated or veined falls where one would expect to see locally variable metal concentrations. After separating falls from finds, a very narrow range of susceptibility values can characterize H, L, and LL ordinary chondrite classes, with practically no overlap (except for some brecciated or veined samples). On the other hand, finds show a variable decrease of susceptibility correlated to the degree to which Earth's water and air have caused the iron in the meteorites to weather and rust. Previous studies had neglected to separate falls from finds, and so had missed this separation of magnetic properties in different ordinary chondrite classes.

From this analysis of a large number of samples, it is clear that finds, even from Antarctica, have to be excluded from efforts to define mean magnetic properties of asteroids related to ordinary chondrites. When finds are excluded, the magnetic properties of meteorites remain in a very narrow range for a given class. The standard deviation for all falls of a given class is only about two times the standard deviation for multiple pieces of the same fall. This supports the hypothesis that all falls from a given ordinary chondrite class (H, L, LL) may come from the same, rather small-sized object. Although magnetic susceptibility cannot be used to classify finds (a weathered H, for example, gives the same value as a fresh L), the magnetic susceptibility of finds can be used to probe weathering stage and to determine if two meteorites found at different locations are part of the same fall ("pairing"). This is a quick way to classify a large number of specimens, for instance, to confirm the identification of meteorites within a large collection.

As a result of these measurements, the classification of about half a dozen samples in the Vatican collection is now being reevaluated. Intriguingly, the work described above suggests that by measuring the magnetic properties of rock remotely, spacecraft may be able to determine with great precision the iron content of asteroids or even materials on the surface of terrestrial planets.

Asteroids

The number of asteroid bulk-density measurements has been rapidly increasing, thanks to spacecraft missions, observations of asteroid satellites, and observations of asteroid mutual gravitational events. In most cases, asteroid bulk densities tend to be substantially below likely meteorite analogs, indicating significant porosity (as described in previous Annual Reports). The bulk porosity of these asteroids can be estimated by using the grain density data of the analog meteorites to constrain the amount of pore space that would be required for an object of that composition and measured bulk density. For example, 433 Eros has a measured bulk density of 2.67 ± 0.03 g/cm³ and probably has an L-chondrite composition, which implies a grain density of 3.75 g/cm³. To make the L-chondrite grain density consistent with the asteroidal bulk density would require a bulk porosity of 28.8%. To better assess asteroidal structure, BRITT (University of Tennessee), CONSOLMAGNO, YEOMANS (Jet Propulsion Laboratory, Pasadena, California) and HOUSEN (Boeing, Seattle, Washington) took the analysis a step further this past year by recognizing that most meteorites have some level of micron-scale microporosity that does not seriously affect the meteorite's cohesive strength. This implies that microporosity would also not affect the parent asteroid's coherent strength. By subtracting the average meteorite analog microporosity from the bulk porosity of an asteroid, we can estimate the asteroid's large-scale macroporosity. An asteroid's macroporosity are the fractures, cracks, and voids that are large enough to affect its coherent strength and define its internal structure. Note that this estimate requires two assumptions: first, that we know the asteroid's meteorite analog and, second, that the meteorites delivered to Earth are a representative sample of that material. Both assumptions are open to debate.

Estimated macroporosities for the asteroids measured so far appear to divide into three rough groups. The first group includes the large asteroids 1 Ceres, 2 Pallas, and 4 Vesta. Their bulk densities are very close to the bulk densities of their analog meteorites, indicating essentially zero macroporosity. These asteroids are probably strong, coherent objects that have not been disrupted throughout solar system history. It is interesting that all three asteroids with diameters >500 km all fall in the zero macroporosity group. The second group includes the S asteroids 433 Eros and 243 Ida, as well as 762 Pulcova and 121 Hermione. These asteroids have between 15 and 25% macroporosity, indicating that they have been extensively fractured. However, this fracturing was probably not extensive enough to disrupt the object, and asteroids with less than approximately 25% macroporosity probably have some measure of coherent strength. In terrestrial geology, well-sorted sedimentary rocks can have up to 30% porosity and still be coherent. However, greater than 30% porosity usually indicates loose rubble or soils. The third group are those asteroids with greater than 30% macroporosity. These objects are probably pervasively fractured and may have been disrupted and reassembled by mutual gravity.

Asteroid 16 Psyche is likely the most porous object obser ved so far. Its reflectance spectra and radar albedo strongly indicate a metallic surface composition. Assuming an iron meteorite grain density of 7.4 g/cm³, the asteroid's inferred low bulk density would require a bulk porosity of 75%, which suggests a pervasively disrupted object that has been loosely reassembled and held together by mutual gravitation. Simulations of impacts into porous materials indicate that porosity can dramatically affect the evolution of asteroid regoliths, impact ejecta, and structure. Impacts into high-porosity asteroids create craters, primarily by compaction and with most ejecta being retained within the crater. As porosity increases, ejecta velocities tend to drop, the sizes of ejecta blankets are reduced, and the efficiency of asteroid impact gardening (the churning up of soil by repeated impacts) is significantly reduced. Because the compaction process dissipates impact shock more effectively, highly porous asteroids may be significantly more resistant to impact disruption and, as a result, have increased dynamical lifetimes.

This new understanding of asteroid structure changes the way we think about how planets were formed from the accretion of small bodies. More importantly, it also changes the way we must think about how to move, or destroy, any "killer" asteroids on a path aimed at Earth. Such rubble piles cannot be simply disrupted by a single well-placed bomb (a la Hollywood), since the rubble will simply dissipate the energy of the explosion. Nor can "pushing" on one end of the asteroid necessarily result in the entire body moving into a new path. On the other hand, one could expect to find a large amount of loose material on such a rubble-pile asteroid. This material could easily be launched from the surface, either to act as "reaction mass" to nudge the body in the opposite direction, or to exploit the material for its mineral wealth.

The Moon

Since the early 1970s our understanding of lunar formation has been dominated by the magma ocean model, that is, that the early Moon started with a layer 400 km thick of completely molten rock, whose stratified freezing gave rise to the different rock types seen in the samples returned by the Apollo mission. However, recent work, spurred in part by the results of the Clementine and Lunar Prospector space missions of the 1990s, has challenged this model on a number of grounds. DYAR (Mount Holyoke College, Mt. Holyoke, Massachusetts) and CONSOLMAGNO have begun a collaboration to explore three specific questions raised by this model.

(1) Is the magma ocean model consistent with the giant-impact origin for the Moon? In the 1980s, ten years after the magma ocean model was proposed, a new theory for the Moon's origin was put forth. This suggested that the Moon formed from material splashed into space by the impact of a large planetesimal onto Earth early in our planet's history. But such an impact-formed Moon, depleted in those elements normally found in an iron core, must have been well mixed and probably completely meltednot to just a depth of 400 kmduring the initial impact and core formation. DYAR and CONSOLMAGNO, along with other workers, have noted that the geophysical constraints on the composition and evolution of such a Moon are difficult to reconcile with the standard magma ocean model.

(2) Did a chilled anorthosite crust exist? The magma ocean model predicts that the upper 60 km of the Moon would be made primarily of the calcium- and aluminum-rich mineral anorthite, the main constituent of anorthosite rocks. But data from the recent lunar orbiters indicate that the average crustal composition of the Moon is significantly different from the composition of the limited Apollo samples on which the magma ocean hypothesis was based. Lunar anorthosites may have formed over too long a period to be consistent with a rapidly chilled crust. And the thorough melting of asteroid Vesta, believed to be the source of basaltic meteorites, apparently did not form anorthosite meteorites; none have ever been found. CONSOLMAGNO and DYAR have begun to look at models of the Moon analogous to the successful chemical models of Vesta, which include more pervasive equilibrium and significant mixing during melting, rather than the stratified layers implied by the lunar magma ocean model.

(3) Is the depletion of volatiles in both the Moon and Vesta (the basaltic meteorite parent body) primordial? We know that both the Moon and the basaltic meteorites are depleted in water, oxygen, and elements like sodium and potassium. The standard magma ocean model assumes that these volatiles were never present once the Moon was formed. Some authors suggest that they were lost during the giant impact formation of the Moon. But this would not explain why they are lost in the same way on Vesta, which presumably was not the result of a giant impact. Other authors have suggested that the loss of volatiles could have occurred during fire-fountain volcanism. DYAR and CONSOLMAGNO note that the abundant vesicles ("frozen bubbles") seen in pristine lunar basalts and basaltic meteorites (including samples in the Vatican collection at Castel Gandolfo) suggest both the Moon and Vesta were much richer in oxygen and other gases than the magma ocean model supposes. New Mossbauer and micro-XANES measurements by DYAR have found ferric (oxidized) iron in lunar anorthosites, which also suggests that the early Moon was originally more oxygen rich than seen today. DYAR's work suggests that large-scale shock reduction and dehydrogenation are also possible for these rocks. Further measurements of both additional lunar samples and basaltic meteorite samples from the Vatican collection should help us understand this problem further.

The significance of this work extends far beyond the Moon. The concept of a "magma ocean" has been borrowed to explain terrestrial bodies from Mercury to Vesta. Until these basic challenges to the lunar magma ocean model are resolved, we will not be able to make progress in understanding the other terrestrial planets. If the magma ocean hypothesis survives these challenges, it will be a theory we can use with greater confidence; if it fails, everything we know about the origin of the terrestrial planets will need to be rethought.

Small Outer Solar System Objects

Observations of Kuiper Belt Objects (KBOs) continued at the VATT through 2001. ROMANISHIN (University of Oklahoma), TEGLER and BOTTHOF (Northern Arizona University, Flagstaff), RETTIG (University of Notre Dame), and CONSOLMAGNO obtained optical (B, V, and R filter) photometry of KBO (26308), 1998 SM165, over eight nights in the fall observing seasons of 1999, 2000, and 2001. These data were analyzed to show a light curve with a large amplitude and a rotational period of 7.98 hours (assuming the brightness variations are due to shape). If this is an ellipsoidal body with a uniform albedo of 0.04, typical of KBOs, it must have dimensions of 600 × 360 × 360 km. That would make (26308) one of the largest, significantly non-spherical bodies in the solar system. Data from 1999 and 2000 show no evidence of color variations with rotational phase. Color versus phase data, obtained during a second run at the VATT in the fall of 2001 by TEGLER and ROMANISHIN, may shed further light on the nature of this object's surface materials.

History and Philosophy of Science; Interdisciplinary Studies

IGEA has finished a paper on the religious implications of the origin of the universe in preparation for a conference on science and religion that will be held in Puebla, Mexico. He explores the possibility of having a self-explanatory theory of the universe and its knowledgeability by human reason.

Recent work by STOEGER on the philosophy of cosmology has yielded an article in Philosophy in Science describing, from a philosophical point of view, "the universe which cosmology studies." With PACHOLCZYK (University of Arizona), he has also written a paper treating problems connected with correspondence, the succession of acceptable theories (e.g., Newton's theory of gravity and Einstein's general relativity), and the notions of truth associated with them.

STOEGER has been continuing his work in formulating a theology of creation in light of contemporary scientific knowledge. As part of this effort, he is in the preliminary stages of developing a philosophy of relations and causes, which would more adequately delineate and connect these concepts at the scientific, ontological, and theological levels, relying on the insight that relations are more basic than causes.

CARUANA has published a textbook entitled Fondamenti Filosofici delle Scienze Naturali (Philosophical Foundations of the Natural Sciences), directed primarily at philosophy undergraduates. It includes a presentation of the basic philosophical arguments on scientific methodology and on the general nature of things. This Italian edition is meant primarily for students attending the Pontifical Gregorian University.

RIBEIRO, a Vatican Observatory Research Group visiting scholar, with VIDEIRA (both from Department of Philosophy, Federal University of Rio de Janeiro) is working on a Brazilian Portuguese edition of the book by STOEGER, The Laws of Nature, the Range of Human Knowledge and Divine Action, which was originally published in Poland by Biblos in 1996. It will be published by the Paulinas Publishing House in São Paulo.

CARREIRA has prepared a study on the interpretation of the anthropic principle as an indication of a design at the origins of the universe. The study is being readied for publication in La Civiltà Cattolica.

As described in the "From the Director" section of this Annual Report, MAFFEO has written The Vatican Observatory: In the Service of Nine Popes, a revised and enlarged edition of his earlier history of the Vatican Observatory. The new book has been published in both English and Italian.