Broadband Photometry of the Potentially Hazardous Asteroid 2010 GU21
ATel #2592; M. Hicks (JPL/Caltech), J. Somers (Moorpark), J. Foster (CSULA), A. McAuley (CSULA)
on 30 Apr 2010; 21:51 UT
Credential Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)
Subjects: Optical, Asteroid, Planet (minor), Solar System Object
Referred to by ATel #: 2604
The Near-Earth Asteroid (NEA) 2010 GU21 was discovered by the Catalina
Sky Survey on April 5 2010 (MPEC 2010-G55) and has been designated as
a Potentially Hazardous Asteroid (PHA) by the Minor Planet Center. We
obtained Bessel BVRI photometry over the course of three nights at the
JPL Table Mountain 0.6-m telescope (TMO), as illustrated in
and summarized in Table 1. Though the nights were clear and photometric
to the 1-3% level, the high humidity, nearly full Moon, and low lunar
elongation hampered our observations. 2010 GU21 will pass within
approximately 8 lunar distances on May 05.25 2010 UT. This object
can be considered a potential low delta-V spacecraft rendezvous
target (dV=6.18 km/s).
The rotationally averaged colors
(B-R=1.114+/-0.028 mag; V-R=0.402+/-0.020 mag; R-I=0.376+/-0.019 mag)
of 2010 GU21 were found most
compatible with an Xc-type spectral classification, an association
obtained through a comparison of our colors with the 1341 asteroid
spectra in the SMASS II database (Bus & Binzel 2002)
[Figure 4 and Table 2].
X-type asteroids include high albedo E-types, moderate albedo M-types,
and low-albedo P-type asteroids (Barucci & Tholen 1989). Moderate
resolution spectroscopy, thermal flux measurements, and/or solar phase
curves would be very useful in resolving this ambiguity. 2010 GU21
remains brighter than V=18 (our nominal cut-off for photometry at TMO) and
at moderate declinations until May 10 2010 UT. We welcome collaborations
with other observers.
Our light-time corrected photometry was converted to reduced magnitude
assuming a phase parameter G=0.05, consistent with a low-albedo asteroid.
The BVI data were registered to R using our nightly measured colors.
After converting the photometry from magnitude to flux units, we performed
a rotational period search using standard Fourier techniques.
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 = 4.326+/-0.005 hr, as shown in
Figure 6 .
Our photometry yields an absolute magnitude H_v=20.78+/-0.02 mag, implying
an effective diameter D~200m for an albedo rho=0.05.
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. The student
participation was supported by the National Science Foundation under
REU grant 0852088 to Cal State LA.
Table 1: Observational circumstances.
Solar Lunar Num.
UT DATE r delta Phase Elong. Exp. OBSERVER(S)
[AU] [AU] [deg] [deg]
2010 04 24.33 1.070 0.070 21.3 51.3 114 Somers, Hicks
2010 04 25.37 1.065 0.064 22.1 41.2 103 Foster
2010 04 26.36 1.059 0.058 22.9 33.8 94 McAuley
Table 2: Best-fit SMASS II spectral analogs.
MISFIT OBJECT NAME (THOLEN) (BUS)
0.650 409 Aspasia CX Xc
0.654 1212 Francette P X
0.824 107 Camilla C X
0.824 1196 Sheba X
0.879 92 Undina X Xc
0.905 1327 Namaqua X