Report of the Terrestrial Bodies Science Working Group. Volume 6: The asteroids

Earth-based astronomical observations and laboratory analysis of meteorites provide the only scientific data available on asteroids. These data are summarized and subjects for future investigations are explored. The measurements required for potential missions are discussed and concepts for a multi-asteroid rendezvous mission in the mid-1980's are outlined

Interference filter photometry of periodic comet Ashbrook-Jackson

P/Ashbrook-Jackson has a period of 7.43 years and comes to perihelion at 2.284 AU. It is a low inclination object (12.5 deg) of moderate eccentricity (0.400). In 1963, it made the best possible apparition, coming to perihelion and opposition virtually simultaneously, but no one made physical observations of faint periodic comets in 1963. In 1978 Ashbrook-Jackson came to opposition on Sept. 28, just 40 days after perihelion. It will be just over 100 years before an equally favorable apparition recurs. P/Ashbrook-Jackson was recovered by Pereyra at Cordoba Observatory on April 28, 1977, more than a year and a quarter before perilhelion and already showing a diffuse coma with central condensation. Its helio-centric distance was then 3.7 AU. An extensive program was planned, but equipment problems and weather ultimately limited it to the two nights of data reported here

Swimming Efficiency of Bacterium Escherichia Coli

We use in vivo measurements of swimming bacteria in an optical trap to determine fundamental properties of bacterial propulsion. In particular, we determine the propulsion matrix, which relates the angular velocity of the flagellum to the torques and forces propelling the bacterium. From the propulsion matrix dynamical properties such as forces, torques, swimming speed and power can be obtained from measurements of the angular velocity of the motor. We find significant heterogeneities among different individuals even though all bacteria started from a single colony. The propulsive efficiency, defined as the ratio of the propulsive power output to the rotary power input provided by the motors, is found to be 0.2%.Comment: 6 page

Asteroid amphitrite: Surface composition and prospects for the possible Galileo flyby

Studies of the trajectory of the Galileo mission to Jupiter recently revealed that the spacecraft can pass close to one of the largest asteroids (#29 Amphitrite). NASA has therefore altered the mission plan of the Galileo spacecraft to include a possible close flyby of Amphitrite in early December 1986, if the condition of the spacecraft allows. If this option is actually implemented, Amphitrite will become the only asteroid for which any high-spatial resolution images and reflection spectra will be available. To evaluate the value of this data and place Amphitrite in the context of the more than 600 asteroids for which some compositional information exists. Existing data was reexamined, new telescopic spectra of Amphitrite were obtained, and simulated Galileo data sets were constructed

Tohoku-Hiroshima-Nagoya planetary spectra library: A method for characterizing planets in the visible to near infrared

There has not been a comprehensive framework for comparing spectral data from different planets.Such a framework is needed for the study of extrasolar planets and objects within the solar system. We have undertaken observations to compile a library of planet spectra for all planets, some moons, and some dwarf planets in the solar system to study their general spectroscopic and photometric natures. During May and November of 2008, we acquired spectra for the planets using TRISPEC, which is capable of simultaneous three-band spectroscopy in a wide wavelength range of 0.45 - 2.5 microns with low resolving power (lambda-over-Delta-lambda is 140 - 360). Patterns emerge from comparing the spectra. Analyzing their general spectroscopic and photometric natures, we show that it is possible to distinguish between gas planets, soil planets and ice planets. These methods can be applied to extrasolar observations using low resolution spectrography or broad-band filters. The present planet spectral library is the first library to contain observational spectra for all of the solar system planets, based on simultaneous observations in visible and near infrared wavelengths. This library will be a useful reference for analyzing extrasolar planet spectra, and for calibrating planetary data sets.Comment: 11 pages, 6 figures, Accepted on 28/08/2009 to appear in Section 10. Planets and planetary systems of Astronomy and Astrophysic

Impactor flux and cratering on Ceres and Vesta: Implications for the early Solar System

We study the impactor flux and cratering on Ceres and Vesta caused by the collisional and dynamical evolution of the asteroid Main Belt. We develop a statistical code based on a well-tested model for the simultaneous evolution of the Main Belt and NEA size distributions. This code includes catastrophic collisions and noncollisional removal processes such as the Yarkovsky effect and the orbital resonances. The model assumes that the dynamical depletion of the early Main Belt was very strong, and owing to that, most Main Belt comminution occurred when its dynamical structure was similar to the present one. Our results indicate that the number of D > 1 km Main Belt asteroids striking Ceres and Vesta over the Solar System history are approximately 4 600 and 1 100 respectively. The largest Main Belt asteroids expected to have impacted Ceres and Vesta had diameters of 71.7 km and 21.1 km. The number of D > 0.1 km craters on Ceres is \sim 3.4 \times 10^8 and 6.2 \times 10^7 on Vesta. The number of craters with D > 100 km are 47 on Ceres and 8 on Vesta. Our study indicates that the D = 460 km crater observed on Vesta had to be formed by the impact of a D \sim 66.2 km projectile, which has a probability of occurr \sim 30% over the Solar System history. If significant discrepancies between our results about the cratering on Ceres and Vesta and data obtained from the Dawn Mission were found, they should be linked to a higher degree of collisional evolution during the early Main Belt and/or the existence of the late heavy bombardment. An increase in the collisional activity in the early phase may be provided for an initial configuration of the giant planets consistent with, for example, the Nice model. From this, the Dawn Mission would be able to give us clues about the initial configuration of the early Solar System and its subsequent dynamical evolution.Comment: Accepted for publication in Astronomy and Astrophysic

IR-dust observations of Comet Tempel 2 with CRAF VIMS

Measurement strategies are now being planned for using the Visual and Infrared Mapping Spectrometer (VIMS) to observe the asteroid Hestia, and the nucleus, and the gas and dust in the coma of comet P/Tempel 2 as part of the Comet Rendezvous Asteroid Flyby (CRAF) mission. The spectral range of VIMS will cover wavelengths from 0.35 to 5.2 micrometers, with a spectral resolution of 11 nm from 0.35 to 2.4 micrometers and of 22 nm from 2.4 to 5.2 micrometers. The instantaneous field of view (IFOV) provided by the foreoptics is 0.5 milliradians, and the current design of the instrument provides for a scanning secondary mirror which will scan a swath of length 72 IFOVs. The CRAF high resolution scan platform motion will permit slewing VIMS in a direction perpendicular to the swath. This enables the building of a two dimensional image in any or all wavelength channels. Important measurements of the dust coma will include the onset of early coma activity, the mapping of gas and dust jets and correlations with active nucleus areas, observations of the dust coma from various scattering phase angles, coverage of the low wavelength portion of the thermal radiation, and the 3.4 micrometer hydrocarbon emission. A description of the VIMS instrument is presented

The magneto-optical gradient effect in an exchange-biased thin film: Experimental evidence for classical diffraction theory

The magneto-optical gradient effect decorates the boundaries of in-plane domains even at perpendicular incidence of light in an optical polarization microscope. For its explanation, the classical magneto-optical diffraction theory was previously used to derive the effect from the same gyrotropic interaction as the Kerr effect. In order to explain the symmetry of the experimentally observed contrast on bulk ferromagnetic crystals, planar as well as perpendicular subsurface gradients in the magnetization had to be assumed. This was particularly needed when the surface magnetizations in neighboring domains pointed head-on and a gradient contrast appeared also in conditions of vanishing gyrotropic interaction at the surface. The gradient contrast in such conditions should not appear in very thin films where perpendicular magnetization gradients are not enforced by reduction of magnetostatic energy. Here we present the first experimental confirmation of this expectation, thus closing an experimental gap in verifying the predictions of the diffraction theory