Papers by William Hartmann
Analysis of experimental impacts at the Ames Vertical Gun Facility, described earlier in LPSC abs... more Analysis of experimental impacts at the Ames Vertical Gun Facility, described earlier in LPSC abstracts (Hartmann, 1980, 1981, 1982), has continued. A paper has been prepared interpreting data from 14 impacts into fine regolith-simulating basalt and pumice powers-in vacuo (Hartmann, to be submitted to Icarus).
Icarus, 1991
Diameters of 1.2, 1.0, and 3.4 km are respectively derived for the earth-approaching asteroids 19... more Diameters of 1.2, 1.0, and 3.4 km are respectively derived for the earth-approaching asteroids 1983 RD, 1980 PA, and 1985 DO2, whose spectra are virtually identical to that of the basaltic-surfaced large asteroid, Vesta. While probably not fragments of Vesta, the three asteroids may be fragments of one or more Vesta-like parent bodies; it is suggested that they may be
This data set contains 52-color IR data of asteroids, taken using a double circularly variable fi... more This data set contains 52-color IR data of asteroids, taken using a double circularly variable filter. The short wavelength portion of the CVF covered the octave from 0.8 to 1.6 microns with 3 percent resolution, while the long wavelength portion covered 1.5 to 2.6 microns with 5 percent resolution. Most of the data are unpublished other than in this PDS data set.
Icarus, 1988
We have expanded the available sample of Trojan and HUda lightcurve amplitudes by about a factor ... more We have expanded the available sample of Trojan and HUda lightcurve amplitudes by about a factor of 3. We compare the available sample of lightcurves of 26 Trojan and Hilda asteroids with lightcurves of belt asteroids. The sample of Trojans and Hildas appears to have a greater incidence of high amplitudes than the belt asteroids of comparable size, suggesting more elongated shapes. The 100-km-scale Trojans (and probably the Hildas) currently have only a few percent of the collision frequency of main-belt asteroids. We infer that they have experienced less collisional evolution, possibly affecting their relative degree of fragmentation and hence their shapes. If these results are verified, one promising hypothesis would be that 100-kin-scale primitive planetesimals formed with more irregular shapes than present-day belt asteroids of similar size, which may have been rounded by collisionai erosion. Other hypotheses are discussed.
Bulletin of the American Astronomical Society, Jun 1, 1983
The Astronomical Journal, 1991
Observations of 951 Gaspra in support of the Galileo spacecraft encounter are reported. Photometr... more Observations of 951 Gaspra in support of the Galileo spacecraft encounter are reported. Photometric observations of the asteroid yield a synodic rotational period of 7.042 46 and a slope parameter G of 0.285 + or - 0.005. It is inferred from data obtained on May 18, 1990, that the subearth latitude was higher at that time than it was earlier
Science, 1980
New observations of Trojan asteroid 624, Hektor, in April 1979 establish that the high amplitude ... more New observations of Trojan asteroid 624, Hektor, in April 1979 establish that the high amplitude of the rotational light curve of this object is caused by its elongated shape and not by patches of dark and light albedo on opposing hemispheres. These observations confirm that Hektor is a very unusual object and are consistent with the hypothesis that it may be a compound asteroidformed when two Trojans of comparable size fell together-a rare fossilized example of a planetary accretion process.
Journal of Geophysical Research: Planets, 1993
The study of the near‐Earth object 2201 Oljato has resulted in many surprises in the decade in wh... more The study of the near‐Earth object 2201 Oljato has resulted in many surprises in the decade in which it has been examined. Its orbital properties have been associated with meteor showers, and its modeled orbital evolution is chaotic, a property which might indicate a history related to comets. Telescopic observations of its visible and near‐infrared spectral reflectance, broad‐band visible and near‐infrared photometry, infrared radiometric measurements, and radar echoes are reported here from two apparitions, 1979 and 1983. A look at all available observational data shows that this asteroid has a high radiometric albedo, a property not associated with comet nuclei. In certain wavelength regimes it is classified as an S‐type asteroid, in others, an E‐type, but its overall spectral reflectance is not typical of either taxonomic type, and neither type is thought of as cometlike. Unexpectedly high ultraviolet reflectance at the 1979 apparition was suggested to be the result of residual ...
Icarus, 1978
Articles Articles, All fields, Author, Advanced search. Images Images, Journal/Book title, Volume... more Articles Articles, All fields, Author, Advanced search. Images Images, Journal/Book title, Volume, Issue, Page, Search tips. Font Size: Decrease Font Size Increase Font Size. ... Further size comparisons are given in Table I. Hektor is also substantially bigger than the neighboring ...
Icarus, 1991
... Adu. Space Res. 9(2) 65-71. CRUIKSHANK, DP, WK HARTMANN, AND DJ THOLEN 1985. Colour, albedo, ... more ... Adu. Space Res. 9(2) 65-71. CRUIKSHANK, DP, WK HARTMANN, AND DJ THOLEN 1985. Colour, albedo, and nucleus size of Halley's Comet. Nature 315, 122-124. CRUIKSHANK, DP, AND RHBROWN 1987. Organic matter on asteroid 130 Elektra. Science 238, 183-185. ...
Icarus, 1990
HK colorimetry of "asteroid" 2060 Chiron in 1988 resolves a long-standing ambiguity about the fit... more HK colorimetry of "asteroid" 2060 Chiron in 1988 resolves a long-standing ambiguity about the fit of the visible spectrum to the infrared spectrum confirming that Chiron's spectrum is very neutral, placing it in taxonomic class C. These observations also allowed us to discover that Chiron had brightened anomalously.
Icarus, 1982
... Oct 81 2.55 1.59 7.0 Coma visible P SwiftGehrels 28.34 Sep 81 1.54 0.60 21.0 Stellar image; g... more ... Oct 81 2.55 1.59 7.0 Coma visible P SwiftGehrels 28.34 Sep 81 1.54 0.60 21.0 Stellar image; gas emissions on 30 Sep 25.27 Oct 81 1.42 0.60 35.6 Coma visible 27.36 Oct 81 1.41 0.60 36.4 Coma visible Asteroids 22 Kalliope 27.63 Oct 81 2.61 1.77 10.9 41 Daphne 28.30 Sep ...
Icarus, 1984
Abstract JHK colors of 14 comets are correlated with cometary distance from the Sun. The correlat... more Abstract JHK colors of 14 comets are correlated with cometary distance from the Sun. The correlation could be explained by (1) changes in coma particle size as comets approach the Sun, (2) decrease in the ice/dirt ratio in coma grains as comets approach the Sun, and/or (3) phase reddening. Short-term color changes in individual comets at fixed phase angles suggest that phase reddening does not explain all color changes. Short-term changes are consistent with jets injecting fresh (high ice/dirt) nuclear material into parts of the coma. All colorimetric data are consistent with pristine coma material being relatively low-albedo dirty ice grains colored by carbonaceous dirt like that in RD-type asteroids. Ice sublimation near the Sun may leave residual pure RD dirt grains, explaining the observed color changes.
Reports of Planetary Astronomy 1991, Sep 29, 1991
This program involves telescopic observations of colorimetry, spectroscopy and photometry of smal... more This program involves telescopic observations of colorimetry, spectroscopy and photometry of small bodies of the solar system, emphasizing possible relatic)nships among outer solar system asteroids, comets, and certain satellites. Earth approacher targets of opportunity and lab spectroscopic studies are included.
Science, 1967
diation of the response would seem to be eliminated. Dosages as low as 0.05 jug of carbachol have... more diation of the response would seem to be eliminated. Dosages as low as 0.05 jug of carbachol have produced drinking when applied to brain tissue. Equivalent data on injection into ventricles are not yet available.
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Papers by William Hartmann