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Byline: Y.R. Fernandez (a), C.M. Lisse (b), M.S. Kelley (c), N. Dello Russo (b), A.T. Tokunaga (d), C.E. Woodward (c), D.H. Wooden (e) Keywords: Comet Tempel-1; Infrared observations Abstract: On UT 2005 July 4 we observed Comet 9P/Tempel 1 during its encounter with the Deep Impact flyby spacecraft and impactor. Using the SpeX near-infrared spectrograph mounted on NASA's Infrared Telescope Facility, we obtained 0.8-to-2.5 [mu]m flux-calibrated spectral light curves of the comet for 12 min before and 14 min after impact. Our cadence was just 1.1 s. The light curve shows constant flux before the impact and an overall brightening trend after the impact, but not at a constant rate. Within a 0.8-arcsec-radius circular aperture, the comet rapidly-brightened by 0.63 mag at 1.2 [mu]m in the first minute. Thereafter, brightening was more modest, averaging about 0.091 mag/min at 1.2 [mu]m, although apparently not quite constant. In addition we see a bluing in the spectrum over the post-impact period of about 0.07 mag in J-H and 0.35 mag in J-K. The majority of this bluing happened in the first minute, and the dust only marginally blued after that, in stark contrast to the continued brightening. The photometric behavior in the light curve is due to a combination of crater formation effects, expansion of the ejecta cloud, and evolution of liberated dust grains. The bluing is likely due to an icy component on those grains, and the icy grains would have had to have a devolatilization timescale longer than 14 min (unless they were shielded by the optical depth of the cloud). The bluing could also have been caused by the decrease in the 'typical' size of the dust grains after impact. Ejecta dominated by submicron grains, as inferred from other observations, would have stronger scattering at shorter wavelengths than the much larger grains observed before impact. Author Affiliation: (a) Department of Physics, University of Central Florida, 4000 Central Florida Blvd., Orlando, FL 32816-2385, USA (b) Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Rd., Laurel, MD 20723, USA (c) Department of Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455, USA (d) Institute for Astronomy, University of Hawaii, 2680 Woodlawn Dr., Honolulu, HI 96822, USA (e) NASA/Ames Research Center, MS 245-3, Moffett Field, CA 94035-1000, USA Article History: Received 16 April 2006; Revised 17 September 2006

The Deep Impact mission was designed so that much of the mission-critical science would be done from Earth-based telescopes. These facilities would observe the comet before, during, and after impact [...], On 4 July 2005, many observatories around the world and in space observed the collision of Deep Impact with comet 9P/Tempel 1 or its aftermath. This was an unprecedented coordinated observational campaign. These data show that (i) there was new material after impact that was compositionally different from that seen before impact; (ii) the ratio of dust mass to gas mass in the ejecta was much larger than before impact; (iii) the new activity did not last more than a few days, and by 9 July the comet's behavior was indistinguishable from its pre-impact behavior; and (iv) there were interesting transient phenomena that may be correlated with cratering physics.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2004.10.019 Byline: Y.R. Fernandez (a), S.C. Lowry (b), P.R. Weissman (c), B.E.A. Mueller (d), N.H. Samarasinha (d), M.J.S. Belton (e), K.J. Meech (a) Abstract: We present new, near-aphelion, time series of photometry of Comet 2P/Encke in Cousins-R band. With these light curves we find that the dominant, synodic rotational periodicity is either P.sub.0=11.079[+ or -]0.009h or 2P.sub.0=22.158[+ or -]0.012h. This is in contrast to data from the 1980s published by others that are consistent with 15.08- and 22.6-h periods. Those periods do not satisfy our phased light curves, and also the 1980s data are not easily reconciled with our periods. This could be due to P/Encke having non-principal axis rotation or due to a drift in the rotation period caused by outgassing torques. We observed the comet at five epochs: July, August, September, and October 2001, and September 2002, and the comet was at times intrinsically brighter than expected for a bare nucleus, due to an apparent contribution from an unresolved coma. Three-quarters of the data were obtained in the second and fifth epochs, and we analyzed these two time series using both the phase-dispersion minimization and 'WindowCLEAN' techniques. At both epochs and with both techniques strong periodicities were found near frequencies f.sub.0=2.16d.sup.-1 and f.sub.1=4.35d.sup.-1. By then using visual inspection of the phased light curves to corroborate these frequencies, and by using the data from the other three epochs to properly align light curve features, we were able to derive P.sub.0 and 2P.sub.0 as the only solutions that satisfy all our observations. The periodicity due to f.sub.1 is clearly seen in our data, but we cannot tell from our data alone whether it is a manifestation of the nucleus's shape, non-principal axis rotation, or both. Author Affiliation: (a) Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA (b) Queen's University Belfast, Department of Physics, Belfast, BT7 1NN, United Kingdom (c) Jet Propulsion Laboratory, MS 183-601, 4800 Oak Grove Drive, Pasadena, CA 91109-8099, USA (d) National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719, USA (e) Belton Space Exploration Initiatives, 430 S. Randolph Way, Tucson, AZ 85716, USA

We present the characteristics of the dust comae of two comets, 126P/IRAS, a member of the Halley family (a near-isotropic comet), and 2P/Encke, an ecliptic comet. We have primarily used mid- and far-infrared data obtained by the ISOPHOT instrument aboard the Infrared Space Observatory (ISO) in 1996 and 1997, and mid-infrared data obtained by the SPIRIT III instrument aboard the Midcourse Space Experiment (MSX) in 1996. We find that the dust grains emitted by the two comets have markedly different thermal and physical properties. P/IRAS's dust grain size distribution appears to be similar to that of fellow family member 1P/Halley, with grains smaller than 5 microns dominating by surface area, whereas P/Encke emits a much higher fraction of big (20 [micro]m and higher) grains, with the grain mass distribution being similar to that which is inferred for the interplanetary dust population. P/Encke's dearth of micron-scale grains accounts for its visible-wavelength classification as a 'gassy' comet. These conclusions are based on analyses of both imaging and spectrophotometry of the two comets; this combination provides a powerful way to constrain cometary dust properties. Specifically, P/IRAS was observed preperihelion while 1.71 AU from the Sun, and seen to have a 15-arcmin long mid-infrared dust tail pointing in the antisolar direction. No sunward spike was seen despite the vantage point being nearly in the comet's orbital plane. The tail's total mass at the time was about 8 x [10.sup.9] kg. The spectral energy distribution (SED) is best fit by a modified greybody with temperature T = 265 [+ or -] 15 K and emissivity [epsilon] proportional to a steep power law in wavelength [lambda] : [epsilon] [varies] [[lambda].sup.-[alpha]] where [alpha] = 0.50 [+ or -] 0.20 (2 [sigma]). This temperature is elevated with respect to the expected equilibrium temperature for this heliocentric distance. The dust mass loss rate was between 150-600 kg/s (95% confidence), the dust-to-gas mass loss ratio was about 3.3, and the albedo of the dust was 0.15 [+ or -] 0.03. Carbonaceous material is depleted in the comet's dust by a factor of 2-3, paralleling the [C.sub.2] depletion in P/IRAS's gas coma. P/Encke, on the other hand, observed while 1.17 AU from the Sun, had an SED that is best fit by a Planck function with T = 270 [+ or -] 15 K and no emissivity falloff. The dust mass loss rate was 70-280 kg/s (95% confidence), the dust-to-gas mass loss ratio was about 2.3, and the albedo of the dust was about 0.06 [+ or -] 0.02. These conclusions are consistent with the strongly curved dust tail and bright dust trail seen by Reach et al. (2000; Icarus 148, 80) in their ISO 12-[micro]m imaging of P/Encke. The observed differences in the P/IRAS and P/Encke dust are most likely due to the less evolved and insolated state of the P/IRAS nuclear surface. If the dust emission behavior of P/Encke is typical of other ecliptic comets, then comets are the major supplier of the interplanetary dust cloud. Keywords: Comets; Infrared observations; Photometry; Dust

On UT 2000 August 21 we obtained simultaneous visible and mid-infrared observations of Comet 9P/Tempel 1, the target of the upcoming NASA Discovery Program mission Deep Impact. The comet was still quite active while 2.55 AU from the Sun (post-perihelion). Two independent analyses of our data, one parameterizing the coma morphology and the other modeling infrared spectrophotometry, show that the nucleus's cross section at the time the data were taken corresponds to an effective radius of 3.0 [+ or -] 0.2 km. Based on visible-wavelength photometry of the comet taken during this observing run and others in the summer of 2000, all of which show the rotational modulation of the nucleus's brightness, we find that the infrared data were obtained near the maximum of the light curve. If we assume that the nucleus's light curve had a peak-to-valley range of 0.6 [+ or -] 0.2 mag, then the mean effective radius is 2.6 [+ or -] 0.2 km. Visible-wavelength photometry of the nucleus, including data published by other groups, lets us constrain the nucleus's R-band geometric albedo: 0.072 [+ or -] 0.016. The nucleus's flux contributed about 85% of the light in the mid-infrared images. Keywords: Comets, Tempel 1; Infrared observations