4,095 research outputs found
Physical characterization and origin of binary near-Earth asteroid (175706) 1996 FG3
The near-Earth asteroid (NEA) (175706) 1996 FG3 is a particularly interesting
spacecraft target: a binary asteroid with a low-DeltaV heliocentric orbit. The
orbit of its satellite has provided valuable information about its mass density
while its albedo and colors suggest it is primitive or part of the C-complex
taxonomic grouping. We extend the physical characterization of this object with
new observations of its emission at mid-Infrared (IR) wavelengths and with
near-IR reflection spectroscopy. We derive an area-equivalent system diameter
of 1.90 \pm 0.28 km (corresponding to approximate component diameters of 1.83
km and 0.51 km, respectively) and a geometric albedo of 0.039 \pm 0.012.
1996 FG3 was previously classified as a C-type asteroid, though the combined
0.4--2.5 micron spectrum with thermal correction indicates classification as
B-type; both are consistent with the low measured albedo. Dynamical studies
show that 1996 FG3 has most probably originated in the inner main asteroid
belt. Recent work has suggested the inner Main Belt (142) Polana family as the
possible origin of another low-DeltaV B-type NEA, (101955) 1999 RQ36. A similar
origin for 1996 FG3 would require delivery by the overlapping Jupiter 7:2 and
Mars 5:9 mean motion resonances rather than the nu-6 resonance, and we find
this to be a low probability, but possible, origin.Comment: Published in Ap
Physical Characterization of Warm Spitzer-observed Near-Earth Objects
Near-infrared spectroscopy of Near-Earth Objects (NEOs) connects diagnostic
spectral features to specific surface mineralogies. The combination of
spectroscopy with albedos and diameters derived from thermal infrared
observations can increase the scientific return beyond that of the individual
datasets. To that end, we have completed a spectroscopic observing campaign to
complement the ExploreNEOs Warm Spitzer program that obtained albedos and
diameters of nearly 600 NEOs (Trilling et al. 2010). Here we present the
results of observations using the low-resolution prism mode (~0.7-2.5 microns)
of the SpeX instrument on the NASA Infrared Telescope Facility (IRTF). We also
include near-infrared observations of ExploreNEOs targets from the MIT-UH-IRTF
Joint Campaign for Spectral Reconnaissance. Our dataset includes near-infrared
spectra of 187 ExploreNEOs targets (125 observations of 92 objects from our
survey and 213 observations of 154 objects from the MIT survey). We identify a
taxonomic class for each spectrum and use band parameter analysis to
investigate the mineralogies for the S-, Q-, and V-complex objects. Our
analysis suggests that for spectra that contain near-infrared data but lack the
visible wavelength region, the Bus-DeMeo system misidentifies some S-types as
Q-types. We find no correlation between spectral band parameters and
ExploreNEOs albedos and diameters. We find slightly negative Band Area Ratio
(BAR) correlations with phase angle for Eros and Ivar, but a positive BAR
correlation with phase angle for Ganymed. We find evidence for spectral phase
reddening for Eros, Ganymed, and Ivar. We identify the likely ordinary
chondrite type analog for a subset of our sample. Our resulting proportions of
H, L, and LL ordinary chondrites differ from those calculated for meteorite
falls and in previous studies of ordinary chondrite-like NEOs.Comment: 6 Tables, 9 Figure
Infrared Lightcurves of Near Earth Objects
We present lightcurves and derive periods and amplitudes for a subset of 38
near earth objects (NEOs) observed at 4.5 microns with the IRAC camera on the
the Spitzer Space Telescope, many of them having no previously reported
rotation periods. This subset was chosen from about 1800 IRAC NEO observations
as having obvious periodicity and significant amplitude. For objects where the
period observed did not sample the full rotational period, we derived lower
limits to these parameters based on sinusoidal fits. Lightcurve durations
ranged from 42 to 544 minutes, with derived periods from 16 to 400 minutes. We
discuss the effects of lightcurve variations on the thermal modeling used to
derive diameters and albedos from Spitzer photometry. We find that both
diameters and albedos derived from the lightcurve maxima and minima agree with
our previously published results, even for extreme objects, showing the
conservative nature of the thermal model uncertainties. We also evaluate the
NEO rotation rates, sizes, and their cohesive strengths.Comment: 16 pages, 4 figures, 3 tables, to appear in the Astrophysical Journal
Supplement Serie
Computation of Mini-Jet Inclusive Cross Sections
We apply the theory of parton-parton total cross sections at large ``s", due
to Lipatov and collaborators, to compute the inclusive cross section for jets
which accompany a large ``s" parton scattering process.Comment: 13 page
The Discovery of Cometary Activity in Near-Earth Asteroid (3552) Don Quixote
The near-Earth object (NEO) population, which mainly consists of fragments
from collisions between asteroids in the main asteroid belt, is thought to
include contributions from short-period comets as well. One of the most
promising NEO candidates for a cometary origin is near-Earth asteroid (3552)
Don Quixote, which has never been reported to show activity. Here we present
the discovery of cometary activity in Don Quixote based on thermal-infrared
observations made with the Spitzer Space Telescope in its 3.6 and 4.5 {\mu}m
bands. Our observations clearly show the presence of a coma and a tail in the
4.5 {\mu}m but not in the 3.6 {\mu}m band, which is consistent with molecular
band emission from CO2. Thermal modeling of the combined photometric data on
Don Quixote reveals a diameter of 18.4 (-0.4/+0.3) km and an albedo of 0.03
(-0.01/+0.02), which confirms Don Quixote to be the third-largest known NEO. We
derive an upper limit on the dust production rate of 1.9 kg s^-1 and derive a
CO2 gas production rate of (1.1+-0.1)10^26 molecules s^-1. Spitzer IRS
spectroscopic observations indicate the presence of fine-grained silicates,
perhaps pyroxene rich, on the surface of Don Quixote. Our discovery suggests
that CO2 can be present in near-Earth space over a long time. The presence of
CO2 might also explain that Don Quixote's cometary nature remained hidden for
nearly three decades.Comment: 40 pages, 8 figures, accepted by Ap
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