Electronic Telegram No. 2531 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION CBAT Director: Daniel W. E. Green; Hoffman Lab 209; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbatiau@eps.harvard.edu (alternate cbat@iau.org) URL http://www.cbat.eps.harvard.edu/index.html Prepared using the Tamkin Foundation Computer Network COMET 103P/HARTLEY J. Bauer, Jet Propulsion Laboratory (JPL); R. Walker, Monterey Institute for Research in Astronomy; A. Mainzer and J. Masiero, JPL; R. Beck, F. Masci, and R. Cutri, IPAC, California Institute of Technology; E. Wright, University of California at Los Angeles; and the WISE team -- in collaboration with M. A'Hearn (University of Maryland), K. Meech (University of Hawaii), C. Lisse (Applied Physics Laboratory, 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. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2010 CBAT 2010 November 4 (CBET 2531) Daniel W. E. Green