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
Credential Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)
Subjects: Optical, Asteroid, Planet (minor), Solar System Object
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
