44 research outputs found
A refined model of Pluto's atmosphere (implemented using OSBERT and AMELIA)
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989.Includes bibliographical references (leaves 145-148).by Stephen Michael Slivan.M.S
Spin vectors in the Koronis family: V. Resolving the ambiguous rotation period of (3032) Evans
A sidereal rotation counting approach is demonstrated by resolving an
ambiguity in the synodic rotation period of Koronis family member (3032) Evans,
whose rotation lightcurves' features did not easily distinguish between doubly-
and quadruply-periodic. It confirms that Evans's spin rate does not exceed the
rubble-pile spin barrier and thus presents no inconsistency with being a ~14-km
reaccumulated object. The full spin vector solution for Evans is comparable to
those for the known prograde low-obliquity comparably-fast rotators in the
Koronis family, consistent with having been spun up by YORP thermal radiation
torques.Comment: 8 pages, 6 figures, accepted for publication in Icaru
Twenty years of SpeX: Accuracy limits of spectral slope measurements in asteroid spectroscopy
We examined two decades of SpeX/NASA Infrared Telescope Facility observations
from the Small Main-Belt Asteroid Spectroscopic Survey (SMASS) and the
MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS) to investigate
uncertainties and systematic errors in reflectance spectral slope measurements
of asteroids. From 628 spectra of 11 solar analogs used for calibration of the
asteroid spectra, we derived an uncertainty of 4.2%/micron on slope
measurements over 0.8 to 2.4 micron. Air mass contributes to -0.92%/micron per
0.1 unit air mass difference between the asteroid and the solar analog, and
therefore for an overall 2.8%/micron slope variability in SMASS and MITHNEOS
designed to operate within 1.0 to 1.3 air mass. No additional observing
conditions (including parallactic angle, seeing and humidity) were found to
contribute systematically to slope change. We discuss implications for asteroid
taxonomic classification works. Uncertainties provided in this study should be
accounted for in future compositional investigation of small bodies to
distinguish intrinsic heterogeneities from possible instrumental effects.Comment: 15 pages, 11 figures, accepted for publication in ApJ
Combining asteroid models derived by lightcurve inversion with asteroidal occultation silhouettes
Asteroid sizes can be directly measured by observing occultations of stars by
asteroids. When there are enough observations across the path of the shadow,
the asteroid's projected silhouette can be reconstructed. Asteroid shape models
derived from photometry by the lightcurve inversion method enable us to predict
the orientation of an asteroid for the time of occultation. By scaling the
shape model to fit the occultation chords, we can determine the asteroid size
with a relative accuracy of typically ~ 10%. We combine shape and spin state
models of 44 asteroids (14 of them are new or updated models) with the
available occultation data to derive asteroid effective diameters. In many
cases, occultations allow us to reject one of two possible pole solutions that
were derived from photometry. We show that by combining results obtained from
lightcurve inversion with occultation timings, we can obtain unique physical
models of asteroids.Comment: 33 pages, 45 figures, 4 tables, accepted for publication in Icaru
The Debiased Compositional Distribution of MITHNEOS : Global Match between the Near-Earth and Main-belt Asteroid Populations, and Excess of D-type Near-Earth Objects
We report 491 new near-infrared spectroscopic measurements of 420 near-Earth objects (NEOs) collected on the NASA InfraRed Telescope Facility as part of the MIT-Hawaii NEO Spectroscopic Survey. These measurements were combined with previously published data from Binzel et al. and bias-corrected to derive the intrinsic compositional distribution of the overall NEO population, as well as of subpopulations coming from various escape routes (ERs) in the asteroid belt and beyond. The resulting distributions reflect well the overall compositional gradient of the asteroid belt, with decreasing fractions of silicate-rich (S- and Q-type) bodies and increasing fractions of carbonaceous (B-, C-, D- and P-type) bodies as a function of increasing ER distance from the Sun. The close compositional match between NEOs and their predicted source populations validates dynamical models used to identify ERs and argues against any strong composition change with size in the asteroid belt between similar to 5 km and similar to 100 m. A notable exception comes from the overabundance of D-type NEOs from the 5:2J and, to a lesser extend, the 3:1J and nu (6) ERs, hinting at the presence of a large population of small D-type asteroids in the main belt. Alternatively, this excess may indicate preferential spectral evolution from D-type surfaces to C and P types as a consequence of space weathering, or point to the fact that D-type objects fragment more often than other spectral types in the NEO space. No further evidence for the existence of collisional families in the main belt, below the detection limit of current main-belt surveys, was found in this work.Peer reviewe
Spin-axis alignment of Koronis family asteroids
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1995.Includes bibliographical references (leaves 256-261).by Stephen Michel Slivan.Ph.D