Broadband Photometry of 214869 (2007 PA8): A Slowly Rotating Potentially Hazardous Asteroid.
ATel #4625; M. Hicks (JPL/Caltech), M. Brewer (VCC), J. Somers (Moorpark College)
on 7 Dec 2012; 00:37 UT
Credential Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)
Subjects: Optical, Asteroid, Planet (minor), Near-Earth Object, Potentially Hazardous Asteroid
The near-Earth asteroid 214869 (2007 PA8) was discovered on 2007 August 09 by the LINEAR NEO survey (MPEC 2007-P35). With a Minimum Orbit Intersection Distance MOID=0.0214 AU and expected diameter D~2km, this object has been designated as a Potentially Hazardous Asteroid (PHA) by the IAU Minor Planet Center. Also, with a Tisserand Invarient T_J=2.95, 2007 PA8's orbit is consistent with the Jupiter-family periodic comets. The asteroid was the subject of extensive radar observation with the Goldstone 70-m system during the 2012 apparition (http://www.jpl.nasa.gov/news/news.php?release=2012-350), constraining the object's size, shape, and rotational state. We obtained two nights of Bessel BVRI and three nights of Bessel R observations of the object at the JPL Table Mountain Observatory (TMO) 0.6-m telescope. Our observational circumstances are summarized in Table 1.
The object's rotationally averaged colors (B-R=1.180+/-0.019 mag; V-R=0.415+/ 0.011 mag; R-I=0.326+/-0.010 mag) were found most compatible with an Xc-type spectral classification (Bus Taxonomy)/C-type (Tholen Taxonomy). This association was obtained through a comparison of our colors with the 1341 asteroid spectra in the SMASS II database (Bus & Binzel 2002) [Figure 1 and Table 2]. A solar phase curve generated from our data [Figure 2] yielded an absolute magnitude H_R=16.07 mag and phase parameter g=0.08. Both the object's colors and solar phase behavior are consistent with a relatively dark and primitive surface composition.
Although our photometry was sparse, Fourier analysis allowed us to estimate a best-fit rotational period P_rot=95.1+/-3.4 hr [Figure 3], within the 3-4 day period range reported from the radar observations. Our colors and phase curve allowed us to determine an absolute magnitude H_V = 16.47 mag. For small solar system bodies in this size range (16< H_V <17), 2007 PA8 is rotating quite slowly [98% percentile; Figure 4]. Assuming a geometric albedo rho=0.05, typical for C-type asteroids, we compute an effective diameter D~3km, much larger than the D~1.6km reported by the JPL radar team. 2007 PA8 would require an anomalously high albedo rho=0.18 to to match the radar-derived effective diameter.
Copyright 2012. All rights reserved. The research described in this telegram was carried out at the Jet Propulsion Laboratory, under a contract with the National Aeronautics and Space Administration. The student participation was
supported by the National Science Foundation under REU grant AST-1156756 to Los Angeles City College..
Table 1: Observational Circumstances.
UT Time r delta phase V Filters Observers
[AU] [AU] [deg] [mag]
2012 10 02.26 1.240 0.241 6.4 14.1 R Hicks
2012 10 17.34 1.124 0.132 14.9 13.0 BVRI Brewer, Hicks
2012 10 28.36 1.052 0.068 29.1 11.8 BVRI Somers, Hicks
2012 10 30.35 1.041 0.059 34.3 11.6 R Hicks
2012 10 31.35 1.035 0.055 37.6 11.6 R Hicks
Table 2: Best-fit SMASS II spectral analogs.
Misfit Object Name (Tholen) (Bus)
1.067 1015 Christa C Xc
1.191 4256 Kagamigawa Xc
1.419 209 Dido C Xc
1.741 52 Europa CF C
1.879 2560 Siegma Xc