From The Astronomer's Telegram on 2010 GU21...
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
Password Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)
Subjects: Optical, Asteroids, Planets, Planets (minor), Solar System Objects
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. Figure 5 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.
Link: Astronomer's Telegram (Broadband Photometry of the Potentially Hazardous Asteroid 2010 GU21)
This area will cover relevant news of the threat to the planet from Near Earth Objects (NEOs) including concepts and designs for mitigation. All opinions are those of the author.
Note: Any opinions expressed on the blog are solely those of the author. The site is not sponsored by, nor does it represent the opinions of, any organization, corporation, or other entity.