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Highlights: [•] Significant improvements in the calibration of the EPOXI science instruments. [•] IR spectrometer flat-field calibration file determined. [•] Detailed characterization of Rockwell HAWAII-1R mid-wave IR detector performance. [•] IR spectrometer non-linearity correction derived pixel-by-pixel. [•] Upgrades to EPOXI data processing pipeline are described. [ABSTRACT FROM AUTHOR]

Abstract: NASA’s Stardust–NExT mission used the Stardust spacecraft to deliver a scientific payload, including a panchromatic visible camera designated NAVCAM, to a close flyby of Comet 9P/Tempel 1 in February 2011. Proper interpretation of the NAVCAM images depends on accurate calibration of the camera performance. While the NAVCAM had been calibrated during the primary Stardust mission to Comet 81P/Wild 2 in 2004, that calibration was incomplete and somewhat lacking in fidelity. Substantial improvements in the NAVCAM calibration were achieved during Stardust–NExT in the areas of geometric correction, spatial resolution, and radiometric calibration (in particular, zero-exposure signal levels, shutter time offsets, absolute radiometric response, noise, and scattered light characterization). These improvements will allow upgrades to the calibration of images returned from the Stardust primary mission as well as high-quality calibration of the Stardust–NExT images. The upgraded calibration results have been incorporated into the Stardust–NExT image processing pipeline via new routines and updated constants and files in preparation for archiving calibrated images in the NASA Planetary Data System. [Copyright &y& Elsevier]

Abstract: Re-calibrated near-infrared spectroscopy of the resolved nucleus of Comet 9P/Tempel 1 acquired by the Deep Impact spacecraft has been analyzed by utilizing the post-Stardust-NExT nucleus shape model and spin pole solution, as well as a novel thermophysical model that explicitly accounts for small-scale surface roughness and thermal inertia. We find that the thermal inertia varies measurably across the surface, and that thermal emission from certain regions only can be reproduced satisfactory if surface roughness is accounted for. Particularly, a scarped/pitted terrain that experienced morning sunrise during the flyby is measurably rough (Hapke mean slope angle ∼45°) and has a thermal inertia of at most 50Jm−2 K−1 s−1/2, but probably much lower. However, thick layered terrain and thin layered terrain experiencing local noon during the flyby have a substantially larger thermal inertia, reaching 150Jm−2 K−1 s−1/2 if the surface is as rough as the scarped/pitted terrain, but 200Jm−2 K−1 s−1/2 if the terrain is considered locally flat. Furthermore, the reddening of the nucleus near-infrared 1.5–2.2μm spectrum varies between morphological units, being reddest for thick layered terrain (median value 3.4%kÅ−1) and most neutral for the smooth terrain known to contain surface water ice (median value 3.1%kÅ−1). Thus, Comet 9P/Tempel 1 is heterogeneous in terms of both thermophysical and optical properties, due to formation conditions and/or post-formation processing. [Copyright &y& Elsevier]

Abstract: A flaw in the pre-launch calibration system resulted in an inability to accurately focus the Deep Impact’s High Resolution Instrument (HRI). This defocus resulted in a significant loss of resolution. The nature of the blurring function allows us to use image restoration techniques to retrieve much of the lost resolution. These techniques can produce artifacts in the image such as noise amplification and unwanted oscillations (at the level of 10% of the peak value in the restored point source) in the restored signal. Much useful information, including photometry of point sources, can be extracted from the restored HRI images of Comet Hartley 2, and other images from the Deep Impact spacecraft. In this paper, we present techniques for evaluating the restored images both qualitatively and quantitatively. Monte Carlo techniques are suggested to assess the accuracy of point source photometry. [Copyright &y& Elsevier]

Abstract: We derive the spin state of the nucleus of Comet 103P/Hartley 2, its orientation in space, and its short-term temporal evolution from a mixture of observations taken from the DIXI (Deep Impact Extended Investigation) spacecraft and radar observations. The nucleus is found to spin in an excited long-axis mode (LAM) with its rotational angular momentum per unit mass, M, and rotational energy per unit mass, E, slowly decreasing while the degree of excitation in the spin increases through perihelion passage. M is directed toward (RA, Dec; J2000)=8±4°, 54±1° (obliquity=48±1°). This direction is likely changing, but the change is probably <6° on the sky over the ∼81.6days of the DIXI encounter. The magnitudes of M and E at closest approach (JD 2455505.0831866 2011-11-04 13:59:47.310) are 30.0±0.2m2/s and (1.56±0.02)×10−3 m2/s2 respectively. The period of rotation about the instantaneous spin vector, which points in the direction (RA, Dec; J2000)=300±3.2°, 67±1.3° at the time of closest approach, was 14.1±0.3h. The instantaneous spin vector circulates around M, inclined at an average angle of 33.2±1.3°, with an average period of 18.40±0.13h at the time of closest approach. The period of roll around the principal axis of minimum inertia (“long” axis) at that time is 26.72±0.06h. The long axis is inclined to M by ∼81.2±0.6° on average, slowly decreasing through encounter. We infer that there is a periodic nodding motion of the long axis with half the roll period, i.e., 13.36±0.03h, with amplitude of ∼1° again decreasing through encounter. The periodic variability in the circulation and roll rates during a cycle was at the 2% and 10–14% level respectively. During the encounter there was a secular lengthening of the circulation period of the long axis by 1.3±0.2min/d, in agreement with ground-based estimates, while the period of roll around the long axis changed by ∼−4.4min/d at perihelion. M decreased at a rate of −0.038 (m2/s) per day in a roughly linear fashion. Assuming a bulk density between 230–300kg/m3 and a total volume for the nucleus of 8.09×108 m3, the net torque acting on the nucleus was in the range 0.8–1.1×105 kgm2/s2. In order to bring the spacecraft photometric and imaging data into alignment on the direction of M, the directions of the intermediate and short principal axes of inertia had to be adjusted by 33° (on the sky) from the values indicated by the shape model with an assumed homogeneous interior. The adjusted direction of the intermediate axis is RA, Dec=302°, −16.5°. The morning and evening terminators in the images are identified, and the variation of the insolation at three regions on the nucleus associated with active areas calculated. The plume of water vapor observed in the inner coma is found to be directed close to the direction of local gravity over the sub-solar region for a range of reasonable bulk densities. The plume does not follow the projected normal to the surface at the sub-solar point. [Copyright &y& Elsevier]

Abstract: We have studied the photometric properties of the nucleus of a hyperactive comet, 103P/Hartley 2, at visible wavelengths using the DIXI flyby images with both disk-integrated and disk-resolved analyses. The disk-integrated phase function of the nucleus has a linear slope of 0.046±0.002mag/deg and an absolute magnitude of 18.4±0.1 at V-band. The nucleus displays an overall linear, featureless spectrum between 400nm and 850nm. The linear spectral slope is 7.6±3.6% per 100nm, corresponding to broadband solar-illuminated color indices B–V of 0.75±0.05 and V–R of 0.43±0.04. Disk-resolved photometric analysis with a Hapke model returns a best-fit single-scattering albedo of 0.036±0.006, an asymmetry factor of the Henyey–Greenstein single-particle phase function of −0.46±0.06, and a photometric roughness of 15±10°. The model yields a geometric albedo of 0.045±0.009 and a Bond albedo of 0.012±0.002. The overall photometric variations of the nucleus are small, with an equivalent albedo variation of 15% FWHM, and a color variation of 12% FWHM. Some areas near the terminator visible in the inbound images show an albedo of more than twice the global average value, and a much bluer color than the average nucleus. The overall photometric properties and variations of the nucleus of Hartley 2 are similar to those of the nuclei of Comets Wild 2 and Tempel 1 as studied from previous spacecraft flyby missions at similar resolutions. [Copyright &y& Elsevier]

Abstract: Data from the Extrasolar Planet Observation and Deep Impact Extended Investigation (EPOXI) mission show Comet 103P/Hartley 2 is a bi-lobed, elongated, nearly axially symmetric comet 2.33km in length. Surface features are primarily small mounds <40m across, irregularly-shaped smooth areas on the two lobes, and a smooth but variegated region forming a “waist” between the two lobes. Assuming parts of the comet body approach the shape of an equipotential surface, the mean density of Hartley 2 is modeled to be 200–400kgm−3. Such a mean density suggests mass loss per orbit of >1%. The shape may be the evolutionary product of insolation, sublimation, and temporary deposition of materials controlled by the object’s complex rotation. [Copyright &y& Elsevier]

Abstract: We consider the origin of ∼380 quasi-circular depressions (pits) seen to be distributed in a broad band across the surface of 9P/Tempel 1 and show that possibly ∼96% may be due to outburst activity. Of the rest, <4%, are probably due to a mix of cryo-volcanic collapse events and collisional impacts with asteroidal material. We estimate the mass ejected during the June 14, 2005, mini-outburst on 9P to be in the range (6–30)×104 kg and find that the resulting pit should have a diameter in the range 10–30m. Published locations of mini-outbursts are revised to account for changes in the nucleus shape, rotation rate, and rotation pole that have resulted from observations made during the Stardust-NExT mission. Both of these locations are found to fall in, or on the edge of, the band of pits that encircles the nucleus. We have identified features in high-resolution images near one of these locations as the possible places of origin of the mini-outbursts. These features show close packing of multiple pits in the appropriate diameter range. We consider the distribution of pit diameters and show that the largest pits follow a power–law with exponent −2.24±0.09. Using the June 14, 2005, mini-outburst and the Deep Impact crater to provide a calibration, we establish empirical relationships between pit diameter, D, the total outburst energy, E, and the visual magnitude change, Δm abs, which is the visual amplitude of the outburst referenced to a standard initial brightness. We find Log10 D ∼0.107(±0.004)Δm abs +1.3(±0.4) and Log10 E ∼0.32(±0.01)Δm abs +10.1(±1.2) where the uncertainties represent the range of values for the coefficient rather than formal error. We apply these approximate relationships to the mega-outburst on 17P/Holmes and predict that it left a pit-like scar on the surface with a diameter in the range 160–1300m, that the total energy released was in the range 7×1012–3×1015 J, and that between 6×107 and 1.3×1011 kg of material was ejected from the surface. While these predictions are crude they encompass, particularly near the upper end of the range, the results on kinetic energy release and mass loss found by Reach et al. (Reach, W.T., Vaubaillon, J., Lisse, C.M., Holloway, M., Rho, J. [2010]. Icarus 208, 276–292) based on IR observations of 17P. [Copyright &y& Elsevier]

Abstract: The photometric properties of the nucleus of Comet 9P/Tempel 1 as modeled from the Stardust-NExT images agree with those reported by Li et al. (Li, J.-Y. et al. [2007a]. Icarus 187, 41–55; Li, J.-Y., A’Hearn, M.F., McFadden, L.A., Belton, M.J.S. [2007b]. Icarus 188, 195–211) from Deep Impact images. No significant changes are detectable by comparing the two image-sets taken one comet year apart. The overall photometric variations on the ∼70% of the surface of Tempel 1 observed by Deep Impact and Stardust-NExT are small, with albedo variations of ±10% full-width-at-half-maximum and non-detectable variations in phase function and surface roughness. Some bright surface albedo features visible in the outbound images have an albedo about 25% higher than that of surrounding area. No bright albedo features similar to those ice patches reported by Sunshine et al. (Sunshine, J.M., et al. [2006]. Science 311, 1453–1455) are seen on the outbound side, which was not imaged by DI. The similar global photometric properties among cometary nuclei may indicate that these properties are dominated by cometary activity that results in constant resurfacing on comets. Tiny amounts of ice concentration on their surface can significantly change the local photometric properties. [Copyright &y& Elsevier]

Abstract: The Deep Impact flyby spacecraft includes a 1.05 to 4.8 μm infrared (IR) spectrometer. Although ice was not observed on the surface in the impact region, strong absorptions near 3 μm due to water ice are detected in IR measurements of the ejecta from the impact event. Absorptions from water ice occur throughout the IR dataset beginning three seconds after impact through the end of observations, ∼45 min after impact. Spatially and temporally resolved IR spectra of the ejecta are analyzed in conjunction with laboratory impact experiments. The results imply an internal stratigraphy for Tempel 1 consisting of devolatilized materials transitioning to unaltered components at a depth of approximately one meter. At greater depths, which are thermally isolated from the surface, water ice is present. Up to depths of 10 to 20 m, the maximum depths excavated by the impact, these pristine materials consist of very fine grained () water ice particles, which are free from refractory impurities. [Copyright &y& Elsevier]

Abstract: The Deep Impact flyby spacecraft includes a 1.05 to 4.8 μm infrared (IR) spectrometer. Although ice was not observed on the surface in the impact region, strong absorptions near 3 μm due to water ice are detected in IR measurements of the ejecta from the impact event. Absorptions from water ice occur throughout the IR dataset beginning three seconds after impact through the end of observations, ∼45 min after impact. Spatially and temporally resolved IR spectra of the ejecta are analyzed in conjunction with laboratory impact experiments. The results imply an internal stratigraphy for Tempel 1 consisting of devolatilized materials transitioning to unaltered components at a depth of approximately one meter. At greater depths, which are thermally isolated from the surface, water ice is present. Up to depths of 10 to 20 m, the maximum depths excavated by the impact, these pristine materials consist of very fine grained () water ice particles, which are free from refractory impurities. [Copyright &y& Elsevier]

Abstract: Galileo''s Solid State Imager (SSI) observed Tvashtar Catena four times between November 1999 and October 2001, providing a unique look at a distinctive high latitude volcanic complex on Io. The first observation (orbit I25, November 1999) resolved, for the first time, an active extraterrestrial fissure eruption; the brightness temperature was at least 1300 K. The second observation (orbit I27, February 2000) showed a large () region with many, small, hot, regions of active lava. The third observation was taken in conjunction with Cassini imaging in December 2000 and showed a Pele-like, annular plume deposit. The Cassini images revealed an high Pele-type plume above Tvashtar Catena. The final Galileo SSI observation of Tvashtar (orbit I32, October 2001), revealed that obvious (to SSI) activity had ceased, although data from Galileo''s Near Infrared Mapping Spectrometer (NIMS) indicated that there was still significant thermal emission from the Tvashtar region. In this paper, we primarily analyze the style of eruption during orbit I27 (February 2000). Comparison with a lava flow cooling model indicates that the behavior of the Tvashtar eruption during I27 does not match that of simple advancing lava flows. Instead, it may be an active lava lake or a complex set of lava flows with episodic, overlapping eruptions. The highest reliable color temperature is . Although higher temperatures cannot be ruled out, they do not need to be invoked to fit the observed data. The total power output from the active lavas in February 2000 was at least . [Copyright &y& Elsevier]

We present the observations of Io acquired by the Solid State Imaging (SSI) experiment during the Galileo Millennium Mission (GMM) and the strategy we used to plan the exploration of Io. Despite Galileo''s tight restrictions on data volume and downlink capability and several spacecraft and camera anomalies due to the intense radiation close to Jupiter, there were many successful SSI observations during GMM. Four giant, high-latitude plumes, including the largest plume ever observed on Io, were documented over a period of eight months; only faint evidence of such plumes had been seen since the Voyager 2 encounter, despite monitoring by Galileo during the previous five years. Moreover, the source of one of the plumes was Tvashtar Catena, demonstrating that a single site can exhibit remarkably diverse eruption styles—from a curtain of lava fountains, to extensive surface flows, and finally a ∼400 km high plume—over a relatively short period of time (∼13 months between orbits I25 and G29). Despite this substantial activity, no evidence of any truly new volcanic center was seen during the six years of Galileo observations. The recent observations also revealed details of mass wasting processes acting on Io. Slumping and landsliding dominate and occur in close proximity to each other, demonstrating spatial variation in material properties over distances of several kilometers. However, despite the ubiquitous evidence for mass wasting, the rate of volcanic resurfacing seems to dominate; the floors of paterae in proximity to mountains are generally free of debris. Finally, the highest resolution observations obtained during Galileo''s final encounters with Io provided further evidence for a wide diversity of surface processes at work on Io. [Copyright &y& Elsevier]