Thursday, May 26, 2011, 8:00 AM - 12:00 PM

Thursday, May 26, 2011, 8:00 AM - 12:00 PM

405

The Sun and Solar System II

Poster Session

Essex Ballroom

405.01

8:00 AM - 12:00 PM

Last year’s launch of the Solar Dynamics Observatory (SDO) has provided additional data to constrain the temperature of coronal loops, allowing for a more detailed analysis of the nature of the heating. Specifically, the high temperature constraints that have been missing from prior analyses are now available to be considered. Images from a coronal loop on the solar disk on December 10, 2010 from both the Atmospheric Imaging Assembly (AIA) and the X-Ray Telescope (XRT) instruments onboard SDO are analyzed along with data from the same date taken by the Extreme Ultraviolet Imaging Spectrometer (EIS) instrument onboard Hinode. Differential emission measure techniques are used to consider whether the loops are isothermal or multithermal in nature. Conclusions regarding the comparison of this data will be presented.

405.02

8:00 AM - 12:00 PM

An artificial intelligence program, AutoClass, which was developed by NASA's Artificial Intelligence Branch, uses Bayesian classification theory to automatically choose the most probable classification distribution to describe a dataset. To investigate its usefulness to the Planetary Science community, we tested its ability to reproduce the taxonomic classes as defined by Tholen and Barucci (1989). Of the 406 asteroids from the Eight Color Asteroid Survey (ECAS) we chose for our test, 346 were firmly classified and all but 3 (<1%) were classified by Autoclass as they had been in the previous classification system (Walker et al., 2011). We are now applying it to larger datasets to improve the taxonomy of currently unclassified objects. Having demonstrated AutoClass’s ability to recreate existing classification effectively, we extended this work to investigations of albedo-based classification systems. To determine how predictive albedo can be, we used data from the Infrared Astronomical Satellite (IRAS) database in conjunction with the large Sloan Digital Sky Survey (SDSS), which contains color and position data for over 200,000 classified and unclassified asteroids (Ivesic et al., 2001). To judge our success we compared our results with a similar approach to classifying objects using IRAS albedo and asteroid color by Tedesco et al. (1989). Understanding the distribution of the taxonomic classes is important to understanding the history and evolution of our Solar System. AutoClass’s success in categorizing ECAS, IRAS and SDSS asteroidal data highlights its potential to scan large domains for natural classes in small solar system objects. Based upon our AutoClass results, we intend to make testable predictions about asteroids observed with the Wide-field Infrared Survey Explorer (WISE).

405.03
WISE Observations of Primitive Asteroid Families

8:00 AM - 12:00 PM

NASA's Wide-field Survey Explorer (WISE) mapped the sky in four bands at 3.4, 4.6, 12, and 22 μm during its mission. Published on 14 April 2011, the WISE Preliminary Release provides data of more than 150,000 asteroids that were processed with initial calibration and reduction algorithms. Our aim is to carry out an analysis of key physical parameters (size, albedo, and thermal properties) of outer main-belt asteroid families. Our study concentrates on the Themis, Veritas, and Hygeia families, but will also include other primitive families (taxonomic types C, P, and D). For each of our target asteroids in the WISE preliminary release, we estimated diameters and albedos by fitting thermal models to the measured fluxes, thus constraining their size distribution and compositions. Our initial results from WISE are part of a more extensive study that includes visible, near-infrared, and mid-infrared spectroscopy. These asteroid families are believed to have experienced less heating than most other asteroids and comparisons with Jupiter Trojans, cometary nuclei, and primitive meteorites can provide strong tests of dynamical and collisional models that relate outer belt asteroids with Transneptunian objects.

405.04

8:00 AM - 12:00 PM

Space missions to study the composition and formation histories of multiple asteroid systems require the identification of safe orbits for the observing spacecraft. To identify regions of orbital stability, we developed an n-body simulation and Monte Carlo scheme to test a large selection of orbits around the components of multiple asteroid systems. Our n-body program integrates the equations of motion of the spacecraft, asteroid system components, and the sun for 20 days, taking into account solar radiation pressure on the spacecraft and modeling asteroids as systems of rigid points when their shape model is known. We utilized a Monte Carlo scheme to test the stability of polar and retrograde orbits from uniformly distributed starting positions with normally distributed tangential velocities around each component. We present preliminary results of simulations testing hundreds of thousands of polar and retrograde orbits around the components of the 2001 SN263 near-earth triple asteroid system, and the (90) Antiope doublet and (45) Eugenia triple systems in the main-belt. These systems are potential targets for several space mission concepts, including: the Amor mission to visit and land on the components of 2001 SN263, Jones et al. (LPSC 42, #2695, 2011), the Diversity mission to explore several asteroid systems including (45) Eugenia and (90) Antiope, Marchis et al. (LPSC 42, #2062, 2011), and the ASTER mission to visit a NEA multiple asteroid, Sukhanov et al. (Cosmic Research 48-5, p. 443-450, 2010). Analysis of stable regions in position and velocity may assist in planning scientific orbits and instrumental specifications for such missions.

405.05
A Lightcurve and Color Analysis of Asteroid 4709 Ennomos

Thomas Harvell¹, J. Ziffer¹, Y. R. Fernandez², M. Reuillard¹, M. E. Walker^1
1University of Southern Maine, ²University of Central Florida.

8:00 AM - 12:00 PM

We will present results from our study of the Jovian Trojan asteroid 4709 Ennomos, an asteroid with an unusually high estimated albedo. Large Trojan asteroids (radius > 25 km) have a mean V-band geometric albedo of 0.041 with very little variation (standard deviation = 0.007 ; Fernandez et. al. 2003). Smaller Trojan asteroids, with radius < 25 km, have both higher albedo (mean = 0.12) and wider variation (standard deviation = 0.065; Fernandez et. al. 2010). Asteroid 4709 Ennomos has a radius of about 38 km and a geometric albedo of about 0.15: several standard deviations above the mean albedo of other large Trojans, but very similar to the albedos of small Trojans. One plausible explanation of Ennomos’ apparently high albedo is that its rotation period may be sufficiently fast so as to invalidate the use of a low-thermal memory thermal model to calculate its size and albedo--the model used for Ennomos. To test this hypothesis, we obtained time series CCD photometry of Ennomos’ light curve using the University of Hawaii 88-inch telescope on UT February 8 through 10, 2003. Analysis of Ennomos’ light curve and rotation period will determine if an isothermal latitude model is more appropriate. Since asteroids of Ennomos’ size, both Trojans and Main-Belt, tend to be relatively slow rotators, a high rotation speed would be unusual. We therefore also consider some of the other hypotheses to explain Ennomos’ high albedo. For example, comparing Ennomos’ colors to those of other asteroid groups can give clues to the reason for an elevated albedo. To this end, we also obtained BVRI colors of Ennomos during our 2003 observing run. We will present a comparison between Ennomos’ colors, other published large Trojan and small Trojan colors (e.g. Jewitt & Luu 1990), and small asteroid colors (e.g. Karlsson et al. 2009).

405.06

8:00 AM - 12:00 PM

AutoClass-C, an artificial intelligence program designed to classify large data sets, was developed by NASA to classify stars based upon their infrared colors. Wanting to investigate its ability to classify asteroidal data, we conducted a preliminary test to determine if it could accurately reproduce the Tholen taxonomy using the data from the Eight Color Asteroid Survey (ECAS). For our initial test, we limited ourselves to those asteroids belonging to S, C, or X classes, and to asteroids with a color difference error of less than +/- 0.05 magnitudes. Of those 406 asteroids, AutoClass was able to confidently classify 85%: identifying the remaining asteroids as belonging to more than one class. Of the 346 asteroids that AutoClass classified, all but 3 (<1%) were classified as they had been in the Tholen classification scheme. Inspired by our initial success, we reran AutoClass, this time including IRAS albedos and limiting the asteroids to those that had also been observed and classified in the Bus taxonomy. Of those 258 objects, AutoClass was able to classify 248 with greater than 75% certainty, and ranked albedo, not color, as the most influential factor. Interestingly, AutoClass consistently put P type objects in with the C class (there were 19 P types and 7 X types mixed in with the other 154 C types), and omitted P types from the group associated with the other X types (which had only one rogue B type in with its other 49 X-types). Autoclass classified the remaining classes with a high accuracy: placing one A and one CU type in with an otherwise perfect S group; placing three P type and one T type in an otherwise perfect D group; and placing the four remaining asteroids (V, A, R, and Q) into a class together.