2,775 research outputs found
NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results
The NEOWISE dataset offers the opportunity to study the variations in albedo
for asteroid classification schemes based on visible and near-infrared
observations for a large sample of minor planets. We have determined the
albedos for nearly 1900 asteroids classified by the Tholen, Bus and Bus-DeMeo
taxonomic classification schemes. We find that the S-complex spans a broad
range of bright albedos, partially overlapping the low albedo C-complex at
small sizes. As expected, the X-complex covers a wide range of albedos. The
multi-wavelength infrared coverage provided by NEOWISE allows determination of
the reflectivity at 3.4 and 4.6 m relative to the visible albedo. The
direct computation of the reflectivity at 3.4 and 4.6 m enables a new
means of comparing the various taxonomic classes. Although C, B, D and T
asteroids all have similarly low visible albedos, the D and T types can be
distinguished from the C and B types by examining their relative reflectance at
3.4 and 4.6 m. All of the albedo distributions are strongly affected by
selection biases against small, low albedo objects, as all objects selected for
taxonomic classification were chosen according to their visible light
brightness. Due to these strong selection biases, we are unable to determine
whether or not there are correlations between size, albedo and space
weathering. We argue that the current set of classified asteroids makes any
such correlations difficult to verify. A sample of taxonomically classified
asteroids drawn without significant albedo bias is needed in order to perform
such an analysis.Comment: Accepted to Ap
Constraining multiple systems with GAIA
GAIA will provide observations of some multiple asteroid and dwarf systems.
These observations are a way to determine and improve the quantification of
dynamical parameters, such as the masses and the gravity fields, in these
multiple systems. Here we investigate this problem in the cases of Pluto's and
Eugenia's system. We simulate observations reproducing an approximate planning
of the GAIA observations for both systems, as well as the New Horizons
observations of Pluto. We have developed a numerical model reproducing the
specific behavior of multiple asteroid system around the Sun and fit it to the
simulated observations using least-square method, giving the uncertainties on
the fitted parameters. We found that GAIA will improve significantly the
precision of Pluto's and Charon's mass, as well as Petit Prince's orbital
elements and Eugenia's polar oblateness.Comment: 5 pages, accepted by Planetary and Space Science, Gaia GREAT-SSO-Pis
A revised asteroid polarization-albedo relationship using WISE/NEOWISE data
We present a reanalysis of the relationship between asteroid albedo and
polarization properties using the albedos derived from the Wide-field Infrared
Survey Explorer. We find that the function that best describes this relation is
a three-dimensional linear fit in the space of log(albedo)-log(polarization
slope)-log(minimum polarization). When projected to two dimensions the
parameters of the fit are consistent with those found in previous work. We also
define p* as the quantity of maximal polarization variation when compared with
albedo and present the best fitting albedo-p* relation. Some asteroid taxonomic
types stand out in this three-dimensional space, notably the E, B, and M Tholen
types, while others cluster in clumps coincident with the S- and C-complex
bodies. We note that both low albedo and small (D<30 km) asteroids are
under-represented in the polarimetric sample, and we encourage future
polarimetric surveys to focus on these bodies.Comment: 16 pages, Accepted to Ap
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
Space Weathering on Near-Earth Objects investigated by neutral-particle detection
The ion-sputtering (IS) process is active in many planetary environments in
the Solar System where plasma precipitates directly on the surface (for
instance, Mercury, Moon, Europa). In particular, solar-wind sputtering is one
of the most important agents for the surface erosion of a Near-Earth Object
(NEO), acting together with other surface release processes, such as Photon
Stimulated Desorption (PSD), Thermal Desorption (TD) and Micrometeoroid Impact
Vaporization (MIV). The energy distribution of the IS-released neutrals peaks
at a few eVs and extends up to hundreds of eVs. Since all other release
processes produce particles of lower energies, the presence of neutral atoms in
the energy range above 10 eV and below a few keVs (Sputtered High-Energy Atoms
- SHEA) identifies the IS process. SHEA easily escape from the NEO, due to
NEO's extremely weak gravity. Detection and analysis of SHEA will give
important information on surface-loss processes as well as on surface elemental
composition. The investigation of the active release processes, as a function
of the external conditions and the NEO surface properties, is crucial for
obtaining a clear view of the body's present loss rate as well as for getting
clues on its evolution, which depends significantly on space weather. In this
work, an attempt to analyze the processes that take place on the surface of
these small airless bodies, as a result of their exposure to the space
environment, has been realized. For this reason a new space weathering model
(Space Weathering on NEO - SPAWN), is presented. Moreover, an instrument
concept of a neutral-particle analyzer specifically designed for the
measurement of neutral density and the detection of SHEA from a NEO is proposedComment: 36 page
Efficiency of different selection strategies against boar taint in pigs
The breeding scheme of a Swiss sire line was modeled to compare different target traits and information sources for selection against boar taint. The impact of selection against boar taint on production traits was assessed for different economic weights of boar taint compounds. Genetic gain and breeding costs were evaluated using ZPlan+, a software based on selection index theory, gene flow method and economic modeling. Scenario I reflected the currently practiced breeding strategy as a reference scenario without selection against boar taint. Scenario II incorporated selection against the chemical compounds of boar taint, androstenone (AND), skatole (SKA) and indole (IND) with economic weights of −2.74, −1.69 and −0.99 Euro per unit of the log transformed trait, respectively. As information sources, biopsy-based performance testing of live boars (BPT) was compared with genomic selection (GS) and a combination of both. Scenario III included selection against the subjectively assessed human nose score (HNS) of boar taint. Information sources were either station testing of full and half sibs of the selection candidate or GS against HNS of boar taint compounds. In scenario I, annual genetic gain of log-transformed AND (SKA; IND) was 0.06 (0.09; 0.02) Euro, which was because of favorable genetic correlations with lean meat percentage and meat surface. In scenario II, genetic gain increased to 0.28 (0.20; 0.09) Euro per year when conducting BPT. Compared with BPT, genetic gain was smaller with GS. A combination of BPT and GS only marginally increased annual genetic gain, whereas variable costs per selection candidate augmented from 230 Euro (BPT) to 330 Euro (GS) or 380 Euro (both). The potential of GS was found to be higher when selecting against HNS, which has a low heritability. Annual genetic gain from GS was higher than from station testing of 4 full sibs and 76 half sibs with one or two measurements. The most effective strategy to reduce HNS was selecting against chemical compounds by conducting BPT. Because of heritabilities higher than 0.45 for AND, SKA and IND and high genetic correlations to HNS, the (correlated) response in units of the trait could be increased by 62% compared with scenario III with GS and even by 79% compared with scenario III, with station testing of siblings with two measurements. Increasing the economic weights of boar taint compounds amplified negative effects on average daily gain, drip loss and intramuscular fat percentag
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