Optical photometry of 2012 EG5: Constraints on taxonomy and spin rate.
ATel #4016; M Hicks (JPL/CalTech), S. Teague (VVC), C. Strojia (VVC)
on 4 Apr 2012; 17:55 UT
Credential Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)
Subjects: Optical, Asteroid, Planet (minor), Solar System Object
The Near-Earth Asteroid (NEA) 2012 EG5 was discovered by the Pan-STARRS optical
survey on March 13 2012 (MPEC 2012-E52) and passed within 0.00154 AU of the
Earth on April 01 2012. With an expected diameter between thirty-five and
eighty meters, this object is too small to be considered a Potentially
Hazardous Asteroid (PHA) but its orbit is such that it can be flagged as a
low delta-V object (delta-V = 6.1 km/sec). The NEA has been scheduled for
observation by the JPL planetary radar group on April 4 2012. We obtained
one night of Bessel BVRI photometry at the JPL Table Mountain 0.6-m
telescope (TMO), as illustrated in
and summarized in Table 1.
The rotationally averaged colors of 2012 EG5 (B-R = 1.150 +/- 0.097 mag;
V-R = 0.373 +/- 0.022 mag; R-I = 0.395 +/- 0.032 mag) were found most
consistent with a Ch-type classification (Bus taxonomy), suggesting a low
albedo and steep solar phase behavior. Taxonomy was determined through
a comparison of our colors with the 1341 asteroid spectra in the SMASS
II database (Bus & Binzel 2002) [
and Table 2].
After converting the photometry from magnitude to flux units and
offsetting the BVI photometry by their mean colors, we found a best-fit
synodic period P_syn = 17.52+/-0.04 min [
] using standard Fourier
techniques. This high spin rate is consistent with a monolithic body
maintained by tensile strength and regolith-free except near the poles.
Assuming a solar phase parameter g=0.05, our photometry yields an absolute
magnitude H_V = 23.97 +/- 0.02 mag, implying an effective diameter D~100 m (rho = 0.05).
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 0852088 to Cal State LA. We thank Bill Owen for the use of his scheduled observing time at TMO.
Table 1: Observational circumstances.
UT DATE r delta Phase V Num. Observers
[AU] [AU] [deg] [mag] Exp.
2009 12 26.28 1.003 0.006 49.3 15.0 57 Hicks, Strojia, Teague
Table 2: Best-fit SMASS II spectral analogs.
MISFIT OBJECT NAME (THOLEN) (BUS)
0.364 743 Eugenisis Ch
0.545 51 Nemausa CU Ch
0.813 521 Brixia C Ch
0.854 5438 Lorre C
0.861 91 Aegina CP Ch