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Harris, A. W.

Publications and source records attributed to Harris, A. W..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

SMASS Near-Earth Object Survey: An Album of Results

The Small Main-Belt Asteroid Spectroscopic Survey (SMASS) undertaken at MIT has produced and published visible spectra for more than 1300 main-belt asteroids. The infrared extension of this program (SMASSIR) has produced near-infrared spectra for about 200 main-belt asteroids. In this poster we present visible and near-infrared spectral results for more than 300 near-Earth objects (NEOs) measured during the SMASS and SMASSIR programs and through ongoing observations at Kitt Peak, Palomar, IRTF, and Magellan observatories. The scientific goals for this sample are to deduce the compositional distribution of the near-Earth object population. Knowledge of this distribution will allow the origin and relative hazard of the NEO population to be better understood and will provide the basis for gaining further insights to asteroid-meteorite and asteroid-comet relationships. While a portion of our NEO sample has been published, spectral measurements are newly presented here for more than 250 NEOs. All published SMASS spectra are available at our website http://smass.mit.edu/. These new near-Earth object spectra will also be made available at the SMASS website at the time they are submitted for publication.

Binzel, R. P.↗
NASA NTRS2001

Quantifying the risk posed by potential Earth impacts

Predictions of future potential Earth impacts by near-Earth objects (NEOs) have become commonplace in recent years, and the rate of these detections is likely to accelerate as asteroid survey efforts continue to mature. In this paper we describe the metrics introduced, and we give numerous examples of their application. This enables us to establish in rough terms the levels at which events become interesting to various parties.

asteroid impact hazard↗
NASA NTRS1994

(abstract) Asteroid 4769 Casalia: Intrepretation of Optical Lightcurves Using a Radar-Derived Shape Model

A 167-parameter, 3-D shape model of Castalia, obtained from inversion of delay-Doppler images, constrained the object's subradar latitude on the date of the observations by defining an annular sky region that contains Castalia's pole. We have used the shape model and nominal Hapke parameters for S asteroids to model Castalia lightcurves obtained at Table Mountain Observatory on August 23-25, 1989, at solar phase angles ranging from 58(deg) to 90(deg). This investigation defines the projected pole's azimuthal orientation around the radar line of sight and therefore yields a least-squares estimate of the orientation of Castalia's north or south pole; there is insufficient geometric leverage to distinguish the rotation sense or to estimate values of Hapke parameters. The model lightcurves match the TMO data surprisingly well, given the modest number of shape parameters in the model and the fact that part of the asteroid was not seen by the radar.

asteroid Castalia shape radar 3-D model optical li↗
NASA NTRS1994

The complex lightcurve of 1992 NA

Amor asteroid 1992 NA was monitored during three nights at a large phase angle of -65 deg. The lightcurves obtained did not reveal a repeatable curve with two maxima and two minima. However, some features suggested a periodicity with three maxima and three minima. A satisfactory composite lightcurve of this form was obtained by means of an 'eyeball' fit and by Fourier analysis. Individual and composite lightcurves are presented. The observed colors are consistent with the C class.

Wisniewski, Wieslaw Z.↗
NASA NTRS1993

Light curves and phase relations of the asteroid 55 Pandora

Photoelectric observations of 55 Pandora were performed in Feb.-March 1989 (six nights) in the phase-angle range of 2.5-14 deg and in Sept.-Nov. 1991 (15 nights) in the range 0.5-16.3 deg. The mean amplitudes of the light curves in these oppositions were 0.22m and 0.10m, respectively. The data indicate that Pandora is a typical M-asteroid, and that the high albedo observed by the IRAS satellite does not correspond to reality.

Shevchenko, V. G.↗
NASA NTRS1993

Corvid meteoroids are not ejecta from the Giordano Bruno impact

The study points out three difficulties with the hypothesis of Hartung (1993) that the Corvid meteor system, observed only once in 1937, may be the return of the clump of ejecta from the formation of a lunar crater, specifically, an event recorded in the chronicles of Gervase of Canterbury on June 25, 1178, which Hartung (1976) previously suggested may be an eyewitness account of the formation of the lunar crater Giordano Bruno. On the basis of this, he predicts that another Corvid shower may be observed in 2003 or 2006. This hypothesis is rejected on the contention that it is implausible that a clump of ejecta could be launched into heliocentric orbit with a low enough dispersion in velocity among separate pieces that it would produce a meteor shower in just one year and not others. Subsequent perturbations by the earth on parts of the clump passing near the earth but not impacting would destroy the coherence of the clump on a time scale much shorter than the 759-yr interval proposed. There are so many orbits that could yield a shower after 759 yr that it is unlikely that a prediction of a return in a specific year would be correct.

Harris, A. W.↗
NASA NTRS1993

Lightcurves and phase relations of asteroid 55 Pandora

Photoelectric observations of the asteroid 55 Pandora were carried out in Feb. - Mar. 1989 (6 nights) in range of phase angles Delta alpha = (2.5 - 1.4) deg, and in Sep. - Nov. 1991 (15 nights) Delta alpha = (0.5 - 16.3) deg. Average amplitudes of lightcurves in these oppositions are 0.22 m and 0.10 m, respectively. The value of linear phase coefficients and the absence of spike-effect of alpha less than 2 deg indicate that Pandora is a typical M-asteroid and the high albedo measured by IRAS-satellite is not real.

Shevchenko, V. G.↗
NASA NTRS1993

The Probable Ages of Asteroid Families

There has been considerable debate recently over the ages of the Hirayama families, and in particular if some of the families are very oung(u) It is a straightforward task to estimate the characteristic time of a collision between a body of a given diameter, d_o, by another body of diameter greater of equal to d_1. What is less straightforward is to estimate the critical diameter ratio, d_1/d_o, above which catastrophic disruption occurs, from which one could infer probable ages of the Hirayama families, by knowing the diameter of the parent body, d_o. One can gain some insight into the probable value of d_1/d_o, and of the likely ages of existing families, from the plot below. I have computed the characteristic time between collisions in the asteroid belt of a size ratio greater of equal to d_1/d_o, for 4 sizes of target asteroids, d_o. The solid curves to the lower right are the characteristic times for a single object...

Harris, A. W.↗
NASA NTRS1992

Asteroid 951 Gaspra - Pre-Galileo physical model

An effort is made to derive from Galileo's 1991 encounter of the S-type asteroid 951 Gaspra general lessons that will be applicable to prospective earth-based observations of other asteroids. Attention is accordingly given to the derivation of spin-vector and shape parameters en route to more detailed physical characterization of a given asteroid. A future encounter of Gaspra by Galileo will be required to verify the present model.

Magnusson, P.↗
NASA NTRS1992

Rosat sky survey observations of the eclipsing binary V471 Tauri

Rosat observations of the DA white dwarf + K2V binary system V471 Tauri, obtained during the sky survey phase of the mission, are presented. A lower amplitude shorter time-scale variability is seen in both the soft X-ray and EUV bands. This is associated with the white dwarf pulsations previously discovered by Exosat and also observed at optical wavelengths. The minimum in the EUV light curve is found to coincide with the maximum in the optical. This direct comparison of the phases of the optical and EUV pulses confirms the prediction made by an earlier indirect comparison and shows conclusively that the V471 Tau oscillations cannot arise from nonradial g-mode pulsations in the white dwarf. They are argued to be caused by rotation of the white dwarf with accretion-darkened magnetic poles. On the basis of the EUV and optical pulse shapes, the accretion geometry is studied, and it is estimated that the rate of accretion onto the white dwarf is about (4-11) x 10 exp -13 solar mass/yr.

Barstow, M. A.↗
NASA NTRS1992

Asteroid lightcurve observations from 1981

Photoelectric lightcurve observations in the V band, together with estimates of the mean and maximum reduced magnitudes, are presented for 59 different asteroids; 15 new or significantly revised periods are reported. While fits are generally good for objects with moderate phase-relation slope, poor quality fits remain among the highest and lowest albedo objects studied in virtue of their respectively shallow and steep sloping-phase curves.

Harris, A. W.↗
NASA NTRS1990

The collisional evolution of the spin of a nonspherical body

The nonspherical shapes of asteroids are considered through a generalization of the Harris (1979) model of asteroid spin rates' collisional evolution. Since a body in spin equilibrium rotates about its axis of maximum moment of inertia, the computation of the mean-squared impact parameter through averaging over all directions of flux is not strictly valid; nevertheless, these complications have been found not to alter the conclusions reachable by means of the simpler model.

Harris, A. W.↗