[IAUC] IAUC 9179: 103P [25139-2011/04-R1]

[quai en eps.harvard.edu]

                                                  Circular No. 9179
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
New postal address:  Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
CBATIAU en EPS.HARVARD.EDU           ISSN 0081-0304
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COMET 103P/HARTLEY
     J. K. Harmon, M. C. Nolan, and E. S. Howell, Arecibo
Observatory; and J. D. Giorgini, Jet Propulsion Laboratory,
obtained 150-m-resolution radar images and radar doppler spectra
of comet 103P/Hartley on Oct. 24-27 using the Arecibo Observatory
12.6-cm planetary radar.  The images show the nucleus to be a
highly elongated, bilobate object with a long-axis dimension of at
least 2.2 km.  The images give a preliminary rotation period
estimate of 18.1 +/- 0.3 hours, although a less-likely period of
13.2 hours cannot be ruled out.  The radar cross section of the
nucleus is 0.04 km^2.  The doppler spectra show a broadband echo
component from large (> cm-size) ejected grains in the inner coma.
The radar cross section of the large-grain coma is 0.6 km^2.  This
echo component is preferentially redshifted, indicating that the
bulk of the grain ejection is in the anti-earthward direction.  The
characteristic radial velocity dispersion of the grains is 4 m/s.

     J. Bauer, Jet Propulsion Laboratory (JPL); R. Walker, MIRA;
A. Mainzer and J. Masiero, JPL; R. Beck, F. Masci, and R. Cutri,
IPAC, California Institute of Technology; E. Wright, University of
California, Los Angeles; and the WISE team -- in collaboration with
M. A'Hearn (University of Maryland), K. Meech (University of Hawaii),
C. Lisse (Johns Hopkins University), and Y. Fernandez (University
of Central Florida) -- report initial results based on 12- and 22-
micron infrared photometry of comet 103P taken during May 10-11
(when the comet was at r = 2.3 AU, Delta = 2.0 AU) by the Wide-
field Infrared Survey Explorer (Wright et al. 2010, A.J. 140, in
press).  Analyses of the trail signal present in the stacked image
with an effective exposure time of 158.4 seconds yields optical-
depth values near 6 x 10**-10 at a mean anomaly of 0.3 deg trailing
the comet nucleus, in both 12- and 22-micron bands.  Analysis of
the dust trail yields beta-parameter values ranging from
approximately 1 x 10**-4 to 2 x 10**-4, consistent with derived
mean trail-grain diameters ranging from approximately 1 to 12 mm.
Photometry of the coma at 22 microns, combined with data from the
University of Hawaii 2.2-m telescope obtained by J. Pittichova, K.
Meech, T. Riesen, and H. Kaluna on May 22 [R-band Af(rho) = 0.84
+/- 0.04 in log cm units], provide constraints on the particle size
distribution expressed as a log-number-density/log-mass slope term
(alpha).  Initial results yield values of alpha = -0.88 +/- 0.10 in
[log N(particles/m^2)]/[log mass(kg)] units, steeper than that
found for the inbound particle fluence during the Stardust
encounter of comet 81P (Green et al. 2004, J. Geophys. Res. 109,
E12S04).  The extracted nucleus signal at 12 microns is consistent
with a body of average spherical radius of 0.73 +/- 0.10 km,
assuming an emissivity of 0.9.

                      (C) Copyright 2010 CBAT
2010 November 4                (9179)            Daniel W. E. Green