Near Earth Object studies from the Spitzer Space Telescope
Abstract
We present an overview of the Near Earth Object (NEO) studies carried out using IRAC on the Spitzer Space Telescope. Over 2000 NEOs have been observed in several programs since the start of the Spitzer Warm Mission. Thermal modelling has been used to estimate the albedos and diameters of the NEOs. In the absence of dense photometry for a large population of NEOs, the best method of obtaining a shape distribution comes from sparse photometry and partial lightcurves. We have used 824 partial lightcurves obtained by Spitzer to determine a shape distribution for NEOs. From this data we find a best fit average elongation \frac{b}{a}=0.72 \pm 0.08. We compare this result with a distribution obtained from Pan-STARRS 1 and find it to be in excellent agreement. We also derive periods and amplitudes for a subset of 38 NEOs, many of them having no previously reported rotation periods. For objects where the period observed did not sample the full rotational period, we derived lower limits to these parameters. We also identify an object with rapid spin and diameter D = 519^{+227}_{-116} m and find that for this object a cohesive strength of about 225 Pa is necessary to avoid fission. Major NEO surveys return a small fraction of high albedo objects which do not have clear analogs in the current meteorite population. About 10% of Spitzer-observed NEOs have nominal albedo solutions greater than 0.5. This may be a result of lightcurve variability leading to an incorrect estimate of diameter or inaccurate absolute visual magnitudes. We performed a Monte Carlo analysis on 1500 NEOs observed by Spitzer, sampling the visible and thermal fluxes of all targets in an amplitude range of 0.1 to 1.0 magnitudes to hold the high albedo targets within albedo cutoffs of 0.4, 0.5, and 0.6. Our results suggest that an amplitude of >1.0 magnitudes is required to duplicate the observations. Implementing the mean lightcurve amplitude obtained from the shape distribution we obtained, we provide an upper-limit on the geometric albedo based on composition.
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #50
- Pub Date:
- October 2018
- Bibcode:
- 2018DPS....5040105M