Broadband Photometry of the Potentially Hazardous Asteroid 1999 MN: Suggestive of YORP and/or Tidal Spin-Up?
ATel #2706; M. Hicks (JPL/Caltech), D. Mayes (JPL/Caltech), A. McAuley (CSULA), J. Foster (CSULA)
on 29 Jun 2010; 21:43 UT
Credential Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)
Subjects: Optical, Asteroid, Planet (minor), Solar System Object
1999 MN was discovered by Carl Hergenrother on behalf of the Catalina Sky Survey on June 22 1999 (MPEC 1999-M27) and identified as a Potentially Hazardous Asteroid (PHA) by the Minor Planet Center. The object's low inclination and perihelion distance allows for frequent gravitational encounters with Mercury, Venus, and Earth. 1999 MN passed within 0.033 AU of the Earth on June 4.5 2010. Our Bessel BVRI observations at the JPL Table Mountain Observatory 0.6-m telescope, summarized in Table 1, were scheduled to support Arecibo radar observations obtained in 2004 and 2005.
The plane-of-sky proximity of 1999 MN to the galactic center complicated our analysis. Approximately 1/3 of the exposures were rejected due to stellar contamination. The object's rotationally averaged colors (B-R=1.206+/-0.047 mag; V-R=0.432+/-0.049 mag; R-I=0.221+/-0.056 mag) were found to be most compatible with an Sq 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 1 and Table 2].
Figure 2 illustrates our observed R-band photometry. 1999 MN's solar phase curve [Figure 3] was best fit to first order with absolute magnitude H_R=20.57 mag and solar phase parameter g=0.32, suggesting a moderately high albedo consistent with the Sq taxonomic classification. Our photometry yielded an absolute magnitude H_v=21.00+/-0.06 mag, implying an effective diameter D~160m for an albedo rho=0.25.
After converting our reduced R magnitudes to flux units, we performed a period search using standard Fourier techniques. Figure 4 plots the Fourier model misfit as a function of rotation period 0 < P_syn < 12 hr, with three principle minima near 5.5/8.2/9.3 hours, respectively [Figure 5]. Assuming a double-peaked lightcurve we measured a synodic period P_syn = 5.482+/-0.007 hr [Figure 6], slightly faster than the period found by Hergonrother & Whiteley (2005) P = 5.495 hr and suggesting the possibility of YORP and/or tidal spin-up. Our current data is insufficient to resolve a synodic versus sidereal period determination and we invite collaboration with other observers.
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 -Galactic-
UT Date r delta Phase V Long. Lat. Filter(s) Observer
[AU] [AU] [deg] [mag] [deg] [deg]
2010 06 05.40 1.046 0.034 21.5 15.2 15 -2 BVRI McAuley
2010 06 06.36 1.051 0.037 9.4 15.0 8 8 BVRI Foster
2010 06 08.25 1.060 0.046 11.4 15.6 357 23 BVRI Mayes
2010 06 09.29 1.065 0.052 18.6 16.1 352 28 BVRI Mayes
2010 06 10.33 1.069 0.059 24.4 16.6 348 32 R Mayes
Table 2: Best-fit SMASS II spectral analogs.
Taxonomic Class
Misfit Object Name (Tholen) (Bus)
0.536 4261 Gekko Sq
0.647 1977 Shura Sq
0.716 33 Polyhymnia S Sq
0.886 2427 Kobzar Sq
0.891 7728 Giblin Sq
0.899 180 Garumna S Sq
