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Broadband Photometry of the Potentially Hazardous Asteroid 2010 FC81

ATEL # 2647; M. Hicks (JPL/Caltech), D. Mayes (JPL/Caltech), J. Somers (Moorpark College)
on 27 May 2010; 22:44 UT
Password Certification: Michael D. Hicks (

Subjects: Optical, Asteroids, Planets, Planets (minor), Solar System Objects

The Near-Earth Asteroid (NEA) 2010 FC81 was discovered by the Wide-field Infrared Survey Explorer (WISE) on March 30 2010 (MPEC 2010-FC81) and has been flagged as a Potentially Hazardous Asteroid (PHA) by the Minor Planet Center (MPEC 2010-H79). 2010 FC81 experienced a close-approach with the Earth of 0.047 AU on May 18.2 2010. After its current apparition the object will remain fainter than V = 22 mag until its next close-approach in 2045. The delta-V requirements for a spacecraft rendezvous with this object are modest (dV = 6.52 km/s).

We obtained two nights (May 20+21) of Bessel R-band photometry (exp time = 200 sec) at the JPL Table Mountain 0.6-m telescope (TMO) near Wrightwood California, summarized in Table 1. We attempted a night of BVRI photometry at TMO to determine colors on May 22 but the data taken was unusable due to high humidity and extremely poor seeing.

Our light-time corrected photometry was converted to reduced magnitude assuming a phase parameter G=0.15. Expressing the photometry as flux, we performed a rotational period search using standard Fourier techniques. Figure 1 plots chi-squared 5th and 6th-order Fourier model misfit as a function of assumed rotation period. Assuming a double-peaked lightcurve, we found a best-fit synodic period P_syn = 19.580+/-0.001 min, as shown in Figure 2. This rotation rate implies, for plausible bulk densities, that the shape of 2010 FC81 can not be maintained by self-gravitation alone and that the NEA is a monolithic body, with surface regolith possible only near the poles. Our photometry gave an Absolute Magnitude in the R filter H_R = 21.50+/-0.04 mag. The JPL/HORIZONS Ephemeris service reports an Absolute Magnitude in the visual system (derived using G=0.15, presumably) of H_V = 21.889 mag, and implies a V-R ~ 0.39 mag. Though tentative, we note that this V-R color is more consistent with the spectrally flat C-type asteroids than with the S-family asteroids. A C-type taxonomy would imply a low albedo rho ~ 0.05 and diameter D ~ 250 m. This classification may not be surprising given the object's large aphelion distance (Q = 4.3 AU).

2010 FC81 remains brighter than V=20.0 mag until June 25 2010. Additional observations, especially thermal measurements, spectroscopy, and solar phase curves, would be very useful in resolving the current ambiguity in taxonomy and albedo.

Copyright 2010. 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.

   Table 1:   Observational Circumstances.                                     Solar  Lunar         Num.      UT DATE       r     delta   Phase  Elong.   V    Exp.   OBSERVER                   [AU]    [AU]   [deg]  [deg]  [mag]   2010 05 20.43  1.045   0.049   45.6   75.7   17.2    35    Mayes   2010 05 21.33  1.049   0.050   41.4   71.8   17.1    36    Hicks   

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