Spitzer Observations of Comet 67P/Churyumov-Gerasimenko at 5.5-4.3 AU From the Sun

We report Spitzer Space Telescope observations of comet 67P/Churyumov-Gerasimenko at 5.5 and 4.3 AU from the Sun, post-aphelion. Comet 67P is the primary target of the European Space Agency's Rosetta mission. The Rosetta spacecraft will rendezvous with the nucleus at heliocentric distances similar to our observations. Rotationally resolved observations at 8 and 24 microns (at a heliocentric distance, rh, of 4.8 AU) that sample the size and color-temperature of the nucleus are combined with aphelion R-band light curves observed at the Very Large Telescope (VLT) and yield a mean effective radius of 2.04 +/- 0.11 km, and an R-band geometric albedo of 0.054 +/- 0.006. The amplitudes of the R-band and mid-infrared light curves agree, which suggests that the variability is dominated by the shape of the nucleus. We also detect the dust trail of the comet at 4.8 and 5.5 AU, constrain the grain sizes to be less than or similar to 6 mm, and estimate the impact hazard to Rosetta. We find no evidence for recently ejected dust in our images. If the activity of 67P is consistent from orbit to orbit, then we may expect the Rosetta spacecraft will return images of an inactive or weakly active nucleus as it rendezvous with the comet at rh = 4 AU in 2014.Comment: 19 pages, 2 tables, 10 figures. Accepted for publication in the Astronomical Journa

Absorption Efficiencies of Forsterite. I: DDA Explorations in Grain Shape and Size

We compute the absorption efficiency (Qabs) of forsterite using the discrete dipole approximation (DDA) in order to identify and describe what characteristics of crystal grain shape and size are important to the shape, peak location, and relative strength of spectral features in the 8-40 {\mu}m wavelength range. Using the DDSCAT code, we compute Qabs for non-spherical polyhedral grain shapes with a_eff = 0.1 {\mu}m. The shape characteristics identified are: 1) elongation/reduction along one of three crystallographic axes; 2) asymmetry, such that all three crystallographic axes are of different lengths; and 3) the presence of crystalline faces that are not parallel to a specific crystallographic axis, e.g., non-rectangular prisms and (di)pyramids. Elongation/reduction dominates the locations and shapes of spectral features near 10, 11, 16, 23.5, 27, and 33.5 {\mu}m, while asymmetry and tips are secondary shape effects. Increasing grain sizes (0.1-1.0 {\mu}m) shifts the 10, 11 {\mu}m features systematically towards longer wavelengths and relative to the 11 {\mu}m feature increases the strengths and slightly broadens the longer wavelength features. Seven spectral shape classes are established for crystallographic a-, b-, and c-axes and include columnar and platelet shapes plus non-elongated or equant grain shapes. The spectral shape classes and the effects of grain size have practical application in identifying or excluding columnar, platelet or equant forsterite grain shapes in astrophysical environs. Identification of the shape characteristics of forsterite from 8-40 {\mu}m spectra provides a potential means to probe the temperatures at which forsterite formed.Comment: 55 pages, 15 figure

Evidence of Fragmenting Dust Particles from Near-Simultaneous Optical and Near-IR Photometry and Polarimetry of Comet 73P/Schwassmann-Wachmann 3

We report imaging polarimetry of segments B and C of the Jupiter-family Comet 73P/Schwassmann-Wachmann 3 in the I and H bandpasses at solar phase angles of approximately 35 and 85deg. The level of polarization was typical for active comets, but larger than expected for a Jupiter-family comet. The polarimetric color was slightly red (dP/dL = +1.2 +/- 0.4) at a phase angle of ~ 35deg and either neutral or slightly blue at a phase angle of ~ 85deg. Observations during the closest approach from 2006 May 11-13 achieved a resolution of 35 km at the nucleus. Both segments clearly depart from a 1/rho surface brightness for the first 50 - 200 km from the nucleus. Simulations of radiation driven dust dynamics can reproduce some of the observed coma morphology, but only with a wide distribution of initial dust velocities (at least a factor of 10) for a given grain radius. Grain aggregate breakup and fragmentation are able to reproduce the observed profile perpendicular to the Sun-Comet axis, but fit the observations less well along this axis (into the tail). The required fragmentation is significant, with a reduction in the mean grain aggregate size by about a factor of 10. A combination of the two processes could possibly explain the surface brightness profile of the comet.Comment: 40 pages including 11 figure

Dust in Comet C/2007 N3 (Lulin)

We report optical imaging, optical and near-infrared polarimetry, and Spitzer mid-infrared spectroscopy of comet C/2007 N3 (Lulin). Polarimetric observations were obtained in R (0.676 micron) at phase angles from 0.44 degrees to 21 degrees with simultaneous observations in H (1.65 micron) at 4.0 degrees, exploring the negative branch in polarization. Comet C/2007 N3 (Lulin) shows typical negative polarization in the optical as well as a similar negative branch near-infrared wavelengths. The 10 micron silicate feature is only weakly in emission and according to our thermal models, is consistent with emission from a mixture of silicate and carbon material. We argue that large, low-porosity (akin to Ballistic Particle Cluster Aggregates) rather absorbing aggregate dust particles best explain both the polarimetric and the mid-infrared spectral energy distribution.Comment: 18 pages, 9 figures, 3 table

Mid-Infrared Spectrophotometric Observations of Fragments B and C of Comet 73P/Schwassmann-Wachmann 3

We present mid-infrared spectra and images from the GEMINI-N (+Michelle) observations of fragments SW3-[B] and SW3-[C] of the ecliptic (Jupiter Family) comet 73P/Schwassmann-Wachmann 3 pre-perihelion. We observed fragment B soon after an outburst event (between 2006 April 16 - 26 UT) and detected crystalline silicates. The mineralogy of both fragments was dominated by amorphous carbon and amorphous pyroxene. The grain size distribution (assuming a Hanner modified power-law) for fragment SW3-[B] has a peak grain radius of a_p ~ 0.5 micron, and for fragment SW3-[C], a_p ~ 0.3 micron; both values larger than the peak grain radius of the size distribution for the dust ejected from ecliptic comet 9P/Tempel 1 during the Deep Impact event (a_p = 0.2 micron. The silicate-to-carbon ratio and the silicate crystalline mass fraction for the submicron to micron-size portion of the grain size distribution on the nucleus of fragment SW3-[B] was 1.341 +0.250 -0.253 and 0.335 +0.089 -0.112, respectively, while on the nucleus of fragment SW3-[C] was 0.671 +0.076 -0.076 and 0.257 +0.039 -0.043, respectively. The similarity in mineralogy and grain properties between the two fragments implies that 73P/Schwassmann-Wachmann 3 is homogeneous in composition. The slight differences in grain size distribution and silicate-to-carbon ratio between the two fragments likely arises because SW3-[B] was actively fragmenting throughout its passage while the activity in SW3-[C] was primarily driven by jets. The lack of diverse mineralogy in the fragments SW3-[B] and SW3-[C] of 73P/Schwassmann-Wachmann 3 along with the relatively larger peak in the coma grain size distribution suggests the parent body of this comet may have formed in a region of the solar nebula with different environmental properties than the natal sites where comet C/1995 O1 (Hale-Bopp) and 9P/Tempel 1 nuclei aggregated.Comment: 31 pages, 5 figure, accepted for publication in A

A Spitzer Study of Comets 2P/Encke, 67P/Churyumov-Gerasimenko, and C/2001 HT50 (LINEAR-NEAT)

We present infrared images and spectra of comets 2P/Encke, 67P/Churyumov-Gerasimenko, and C/2001 HT50 (LINEAR-NEAT) as part of a larger program to observe comets inside of 5 AU from the sun with the Spitzer Space Telescope. The nucleus of comet 2P/Encke was observed at two vastly different phase angles (20 degrees and 63 degrees). Model fits to the spectral energy distributions of the nucleus suggest comet Encke's infrared beaming parameter derived from the near-Earth asteroid thermal model may have a phase angle dependence. The observed emission from comet Encke's dust coma is best-modeled using predominately amorphous carbon grains with a grain size distribution that peaks near 0.4 microns, and the silicate contribution by mass to the sub-micron dust coma is constrained to 31%. Comet 67P/Churyumov-Gerasimenko was observed with distinct coma emission in excess of a model nucleus at a heliocentric distance of 5.0 AU. The coma detection suggests that sublimation processes are still active or grains from recent activity remain near the nucleus. Comet C/2001 HT50 (LINEAR-NEAT) showed evidence for crystalline silicates in the spectrum obtained at 3.2 AU and we derive a silicate-to-carbon dust ratio of 0.6. The ratio is an order of magnitude lower than that derived for comets 9P/Tempel 1 during the Deep Impact encounter and C/1995 O1 (Hale-Bopp).Comment: Accepted for publication in the Astrophysical Journal 48 pages, 15 figures, 10 table

Skeletal muscle triglyceride. An aspect of regional adiposity and insulin resistance

Najnowsze dane uzyskane z badań, w których stosowano cztery niezależne metody wskazują, że nadmierne spichrzanie triglicerydów w mięśniach szkieletowych wiąże się z insulinoopornością. Potencjalne mechanizmy tłumaczące ten związek obejmują zlokalizowane w mitochondriach zaburzenia metabolizmu kwasów tłuszczowych w przebiegu otyłości oraz cukrzycy typu 2. Szczególnie dominują zaburzenia ścieżki oksydacyjnej kwasów tłuszczowych w fazie poabsorbcyjnej, które prowadzą do zmniejszonego zużycia oraz nadmiernej estryfikacji oraz spichrzania lipidów w mięśniach szkieletowych. Te zaburzenia metabolizmu kwasów tłuszczowych na czczo mogą się wiązać z niedostosowaniem metabolizmu w insulinooporności, co nie ogranicza się do defektu metabolizmu glukozy w warunkach stymulacji insuliną. Dowody te więc wskazują, że zaburzenia metabolizmu kwasów tłuszczowych odgrywają rolę w procesie gromadzenia triglicerydów mięśni szkieletowych oraz w patogenezie insulinooporności. Zmniejszenie masy ciała poprzez ograniczenie podaży kalorii poprawia wrażliwość na insulinę, ale wpływ na metabolizm kwasów tłuszczowych jest mniej wyraźny. Niemniej jednak obniżenie masy ciała zmniejsza zawartość triglicerydów w mięśniach szkieletowych, być może przyczyniając się do poprawy działania insuliny obserwowanej w miarę odchudzania. Zmiany w metabolizmie substratów w mięśniu szkieletowym pozwalają wyjaśnić związek pomiędzy akumulacją triglicerydów w mięśniu szkieletowym a insulinoopornością, co może prowadzić do zastosowania odpowiedniejszej terapii, mającej na celu poprawę metabolizmu glukozy oraz kwasów tłuszczowych w otyłości oraz w cukrzycy typu 2.Recent evidence derived from four independent methods indicates that an excess triglyceride storage within skeletal muscle is linked to insulin resistance. Potential mechanisms for this association include apparent defects in fatty acid metabolism that are centered at the mitochondria in obesity and in type 2 diabetes. Specifically, defects in the pathways for fatty acid oxidation during postabsorptive conditions are prominent, leading to diminished use of fatty acids and increased esterification and storage of lipid within skeletal muscle. These impairments in fatty acid metabolism during fasting conditions may be related to a metabolic inflexibility in insulin resistance that is not limited to defects in glucose metabolism during insulin-stimulated conditions. Thus, there is substantial evidence implicating perturbations in fatty acid metabolism during accumulation of skeletal muscle triglyceride and in the pathogenesis of insulin resistance. Weight loss by caloric restriction improves insulin sensitivity, but the effects on fatty acid metabolism are less conspicuous. Nevertheless, weight loss decreases the content of triglyceride within skeletal muscle, perhaps contributing to the improvement in insulin action with weight loss. Alterations in skeletal muscle substrate metabolism provide insight into the link between skeletal muscle triglyceride accumulation and insulin resistance, and they may lead to more appropriate therapies to improve glucose and fatty acid metabolism in obesity and in type 2 diabetes

A Review of the MLAS Parachute Systems

The NASA Engineering and Safety Center (NESC) is developing the Max Launch Abort System (MLAS) as a risk-mitigation design should problems arise with the baseline Orion spacecraft launch abort design. The Max in MLAS is dedicated to Max Faget, the renowned NASA spacecraft designer. The MLAS flight test vehicle consists of boost skirt, coast skirt and the MLAS fairing which houses a full scale boilerplate Orion Crew Module (CM). The objective of the flight test is to prove that the CM can be released from the MLAS fairing during pad abort conditions without detrimental recontact between the CM and fairing, achieving performance similar to the Orion launch abort system. The boost and coast skirts provide the necessary thrust and stability to achieve the flight test conditions and are released prior to the test -- much like the Little Joe booster was used in the Apollo Launch Escape System tests. To achieve the test objective, two parachutes are deployed from the fairing to reorient the CM/fairing to a heatshield first orientation. The parachutes then provide the force necessary to reduce the total angle of attack and body angular rates required for safe release of the CM from the fairing. A secondary test objective after CM release from the fairing is to investigate the removal of the CM forward bay cover (FBC) with CM drogue parachutes for the purpose of attempting to synchronously deploying a set of CM main parachutes. Although multiple parachute deployments are used in the MLAS flight test vehicle to complete its objective, there are only two parachute types employed in the flight test. Five of the nine parachutes used for MLAS are 27.6 ft D(sub 0) ribbon parachutes, and the remaining four are standard G-12 cargo parachutes. This paper presents an overview of the 27.6 ft D(sub 0) ribbon parachute system employed on the MLAS flight test vehicle for coast skirt separation, fairing reorientation, and as drogue parachutes for the CM after separation from the fairing. Discussion will include: the process used to select this design, previously proven as a spin/stall recovery parachute; descriptions of all components of the parachute system; the minor modifications necessary to adapt the parachute to the MLAS program; the techniques used to analyze the parachute for the multiple roles it performs; a discussion of the rigging techniques used to interface the parachute system to the vehicle; and a brief description of how the evolution of the program affected parachute usage and analysis. An overview of the Objective system, rationale for the MLAS approach and the future of the program will also be presented. We hope to have flight test results to report at the time of the Conference Presentation