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Results from an observational program to detect weak silicate features on M-type asteroids will be presented. Results include nearly full-rotational coverage of asteroids 69 Hesperia, 110 Lydia, 201 Penelope and 216 Kleopatra. Additional information is contained in the original extended abstract.
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Photoelectric observations of 1915 Quetzalcoatl on March 2, 1981 show that this asteroid has a rotational period of 4.9 + or - 0.3 hr and a lightcurve amplitude of 0.26 magnitudes. B-V and U-B colors are found to be 0.83 + or - 0.04 and 0.43 + or - 0.03, respectively, consistent with Quetzalcoatl being an S-type asteroid. Additional observations from March 31, 1981, give a linear phase coefficient of 0.033 mag/deg and a mean B(1,0) magnitude of 20.10. The resulting estimated mean diameter for Quetzalcoatl is only 0.37 km, making it one of the smallest asteroids for which physical observations have yet been made.
The general problem of satellite and particle dynamics about a uniformly rotating tri-axial ellipsoid with constant density is formulated.
Light curves, UBV colors, rotational periods, phase coefficients, and absolute magnitudes are presented. The asteroids studied are (1) Ceres, (4) Vesta, (16) Psyche, (78) Diana, (281) Lucretia, (451) Patientia, (1212) Francette, and (1362) Griqua. The rotation axis of Lucretia is nearly perpendicular to the plane of the ecliptic. Ceres appears to be nearly spherical with an absolute magnitude of B(1,0)=4.42, which is 0.3 mag fainter than previously reported. The determination of the absolute magnitude for an asteroid depends on its aspect, and for each opposition there is, therefore, a different absolute magnitude.
Radar echoes can furnish high-resolution images of near-Earth asteroids, reveal their rotation states and metal abundances, and improve the accuracy of trajectory predictions a thousandfold, a capability that is important for asteroids making very close Earth approaches and that can dramatically reduce the cost and risk of spacecraft missions.
Photometric observations of the asteroid 37 Fides carried out at four observatories are reported. The data were taken at phase angles ranging from approximately 2-23 deg. A composite of the light curves obtained revealed that, considering a period of 7.33 hr, the full cycle light curve exhibits one maximum and one minimum. An increase in brightness was observed following a primary minimum, a factor that indicated the cyclical appearance and disappearance of a large topographical feature. It is concluded that the 7.33 hr period is the rotational speed of the asteroid, in contrast with a previously held 14.66 hr rotational period. The method is concluded useful for identifying rotational periods of asteroids when only partial light curve data from different sources is available, and when the projections can be checked observationally.
Asteroid shape determinations are presently made by means of a novel technique based on the geometric relation between spectral edge frequencies and the shape of a rotating, rigid radar target. By employing the echo spectra obtained at many rotational phases, the asteroid's convex polar silhouette hull is obtained; noise content is treated as a problem in weighted-least-squares optimization, subject to inequality constraints. The performance of this estimation method is assessed in a series of simulated data giving attention to spectral noise propagation into hull error; sensitivity to echo strength and spectral resolution are also evaluated.
Principal Data Products: Ensemble of L-maps from SPC, Spacecraft state, Asteroid pole and rotation. Secondary Products: Global topography model, inertia tensor, gravity. Composite high resolution topography. Three dimensional image maps.
Review of the rotation period, phase coefficients, and polarization curve of the unusual asteroid Flora. It is an almost spherical asteroid whose period of rotation is probably 13.6 h, but may be only one half of this. Its surface layer consists of a dark material resembling lunar surface soil, but since the polarization curves of Flora and the moon, though generally similar, are not identical the surface of Flora must differ somewhat either in composition or in texture from that of the moon.
By studying the image two-dimensional power spectra or autocorrelations projected by an asteroid as it rotates, it is possible to locate its rotational pole and derive its three axes dimensions through speckle interferometry under certain assumptions of uniform, geometric scattering, and triaxial ellipsoid shape. However, in cases where images can be reconstructed, the need for making the assumptions is obviated. Furthermore, the ultimate goal for speckle interferometry of image reconstruction will lead to mapping albedo features (if they exist) as impact areas or geological units. The first glimpses of the surface of an asteroid were obtained from images of 4 Vesta reconstructed from speckle interferometric observations. These images reveal that Vesta is quite Moon-like in having large hemispheric-scale albedo features. All of its lightcurves can be produced from a simple model developed from the images. Although undoubtedly more intricate than the model, Vesta's lightcurves can be matched by a model with three dark and four bright spots. The dark areas so dominate one hemisphere that a lightcurve minimum occurs when the maximum cross-section area is visible. The triaxial ellipsoid shape derived for Vesta is not consistent with the notion that the asteroid has an equilibrium shape in spite of its having apparently been differentiated.
Ground-based characterization of asteroids that are planned or potential targets of space missions provides important data on their physical parameters and properties. Knowledge of the properties of mission targets is important especially during mission preparation and planning, as it serves to select best or suitable targets for specific purpose of a given mission, to prepare mission plans, to constrain possible mission scenarios, and to design mission experiments. Such characterization efforts may be particularly critical for flyby missions that take only limited data during the high-speed flybys of their target asteroids, but they also provide very crucial data for targets of rendezvous missions. Moreover, long-term observations taken from Earth also allows the modelling of, or constraining, processes acting on the asteroids over extended time scales. Over the past years and decades we have obtained rich data on physical parameters of 82 asteroids that are planned or potential targets of space missions. Our primary observing technique is time-resolved (lightcurve) photometry, but we use also data obtained with other techniques, such as spectroscopy, thermal or radar observations. 15 of the 82 characterized asteroids are planned or possible targets of several space missions that are in flight or preparation, such as ESA’s Hera, RAMSES and PRIAMOS, NASA’s OSIRIS-APEX, JAXA’s Hayabusa2#, DESTINY+ and Next Generation Sample Return (NGSR), the Emirates Mission to Asteroids (EMA), and Karman+’s High Frontier, but we have also characterized 67 asteroids that are potential targets of space missions for their low delta-V’s and were announced as being “of interest to NASA” in the Small-Bodies-Observations- NASA mailing list or listed on the NHATS page of “Accessible NEAs”. The sample of asteroid targets span 3 orders of magnitude in size, with absolute magnitudes H from 12.57 to 26.8, corresponding to diameters from about 10 m to about 10 km. The sample contains a variety of taxonomic types and physically or dynamically interesting objects. Among them, we have identified 5 binary asteroids and 20 tumblers (i.e., asteroids in excited, non-principal axis rotation states). Rotation periods of the characterized asteroids range from 1.45 min to 280 h, reflecting diversity of their properties and formation/evolution paths. We will present an overview of the data set and highlight several representative cases.
Lightcurves for 624 Hektor with Radcliffe, Kitt Peak, Catalina and Cerro Tololo reflectors, noting asteroid shape and rotational axis
The following topics were discussed: A Model for the Formation of Paterae on Io; LIBS-based Detection of As, Br, C, Cl, P, and S in the VUV Spectral Region in a Mars Atmosphere; Mass Independent Sulfur in Achondrites: Possible Evidence of Photochemistry in the Solar Nebula; Grain Size-dependent Viscosity and Oceans in Icy Satellites; Claritas Paleolake Studied from the MEX HRSC Data; Mars Express HRSC Colors of White Rock, Arabia, Mars; Lava and Flows of the Arcadia Region of Mars; Isotopic Composition of Lunar Soils and the Early Differentiation of the Moon; Trace Element Analysis of Lunar Soils by ICP-MS; Highly Siderophile Elements and Osmium Isotope Systematics in Ureilites: Are the Carbonaceous Veins Primary Components?; Evaporative Evolution of Martian Brines Based on Halogens in Nakhlites and MER Samples; Io from High-Resolution Galileo PPR Data Taken Simultaneously with SSI or NIMS Observations; Loki, Io: Groundbased Observations and a Model for Periodic Overturn; Deconstructing a Few Myths in the Interpretation of Satellite-Altitude Crustal Magnetic Field: Examples from Mars Global Surveyor; Semi-Autonomous Rover Operations: A Mars Technology Program Demonstration; Rotational Studies of Asteroids with Small Telescopes; Mineralogy and Temperature-induced Spectral Investigations of A-type Asteroids 246 Asporina and 446 Aeternitas; and Thermal History Calculations Versus Full Convection Models: Application to the Thermal Evolution of Mercury. Recent Solar-Proton Fluxes
The surfaces of near-Earth asteroids are expected to differ significantly from those of large objects like the moon because of their different origin and evolution. A selection of such objects for an extensive procurement of material will also be made on criteria like the surface roughness and the rotation rate with respect to the surface gravity. From the currently known distribution of near-Earth asteroid rotation rates it is shown that a significant fraction of them is rotating near their escape velocities. The determination of macroscopic surface roughness from rotation light curves under an assumption of a fractal surface geometry is discussed. Much information is expected from the variation of harmonic expansions of the light curves with the phase angle.
For over 3 decades, lasers have been a tool of the space programs of the world for accomplishing a variety of engineering and scientific objectives. The majority of these uses have, however, been largely Earth-based and only a few lasers have actually been flown and operated in Earth orbit and even fewer on missions to the planets. However, in the last few years laser altimeters, lidars, and ranging systems have been part of space missions to the moon, an asteroid, and Mars; and more are planned and contemplated in the future exploration of the Earth and solar system. Early in 1994, the Clementine mission was launched to the moon and carried a laser altimeter that made the first systematic topographic survey of the moon during its 2-month observation period. This mission significantly improved our understanding of the shape and topography of the moon and along with gravity information obtained from the tracking data modified some of our thinking about the moon, the thickness of ice crust and the isostatic state of the highlands and basins. On September 11, 1997, the Mars Global Surveyor (MGS) entered into orbit around Mars and the Mars Orbiter Laser Altimeter (MOLA) started to map the topography of the planet to unprecedented accuracy. On its first pass across the planet, MOLA showed large areas of the northern hemisphere to be flatter than any other known surface on Earth or any other body explored to date. In January 1999, the NEAR spacecraft which carries a laser ranger (NLR), will arrive at the S-type asteroid, Eros, and during the following year the NLR will help determine the shape and rotational dynamics of this asteroid. In the Spring of 2000, the Vegetation Canopy Lidar (VCL) mission will be launched and employing a multi-beam laser altimeter (MBLA) will measure the Earth's tree canopy shapes and heights and begin to globally monitor the biomass. The following year, in 2001, the Geoscience Laser Altimeter System, which carries a 2 wavelength laser altimeter of a few centimeter accuracy, will begin a multi-year observation program of the Earth's icecaps, land mass, oceans and the clouds of the atmosphere. At the same time, laser ranging to satellites and the moon is likely to be poised to reach to the planets and track spacecraft throughout the inner solar system by applying optical transponder technology to increase its distance capability.
A period of rotation of 3.0655 + or - 0.0008 hr is presently established for the 1862 Apollo asteroid on the basis of photoelectric light curves obtained during December 1980 and April-May 1982. The slope of the phase curve is typical for a moderate albedo asteroid. A pole position has been calculated using the observed deviation of the light curve from constant periodicity. While the formal uncertainty of the solution for the pole position is less than 10 deg, it may be several times that figure or even entirely wrong.