2001 FE90: An elongated and rapidly rotating near-Earth asteroid.

ATel #2116; M. Hicks (JPL/Caltech), K. Lawrence (JPL/Caltech), H. Rhoades (JPL/Caltech), J. Somers (Moorpark College), A. McAuley (CSULA), T. Barajas (LACC)
on 8 Jul 2009; 22:16 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)

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The Near-Earth Asteroid (NEA) 2001 FE90 (FE90), discovered by B. Skiff during the LONEOS survey, was identified as a Potentially Hazardous Asteroid by the Minor Planet Center. A perigee of 0.018 AU occurred on 2009 June 28.38, near which time FE90 was scheduled to be imaged by the JPL Planetary Radar Team. Our optical observations revealed a small, monolithic, and fast-rotating [P_syn = 28.66+/-0.06 min] NEA. We conclude that FE90 is likely an shard arising from the disruption of a well-differentiated parent body. Southern hemisphere observers are encouraged to collect light-curves of FE90 to facilitate shape/spin modeling. FE90 will remain at declinations near -40 deg and brighter than m_V ~ 19 from early July through mid-August.

Optical spectroscopy was obtained at the Palomar 5-m telescope on the night of June 19.2, see Figure 1. A comparison with ~1300 asteroid spectra in the SMASS II database (Bus & Binzel 2002) found FE90 best matched by the A-type asteroid 289 Nenetta. A-type asteroids are olivine-rich and are thought be the product of partial/full melting of a large parent body (Reddy et al. 2005). Our spectrum was acquired at substantial solar phase angle and until we can quantify the effects of phase reddening, we consider our taxonomic classification tentative.

R-band photometry of FE90 was obtained at the JPL Table Mountain 0.6-m telescope (TMO) over 5 nights from 06/20 to 07/01, see Table 1. Each night's data was analyzed via standard Fourier techniques, as shown in Figures 2 though 6 [2][3][4][5][6]. The light-curve amplitudes were consistent with a minimum 2:1 axial ratio. The rapid rotation of FE90 implies a monolithic body, a density of over 40 gm per cm^3 is required to maintain integrity if strength-free. Two solar phase curves are given in Figure 7, derived using light-curve subtracted measurements (red symbols) and data restricted to near the maximum brightness peaks of the individual light-curves (green symbols). The Maximum Brightness method minimizes the effects of non-spherical shape (Harris & Lupishko 1989). The G values were consistent with a moderate-to-high albedo asteroid. With H_oR = 20.11 mag and the V-R color given in Figure 1, the effective diameter of FE90 is likely near 200 m, assuming an albedo of 0.25.

The research descripbed in this telegram was carried out at the Jet Propulsion Laboratory, under contract with the National Aeronautics and Space Administration.

Table 1: TMO R-band photometry observational summary.