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

3 - 14 Micron Spectroscopy of Comets C/2002 O4 (Honig), C/2002 V1 (NEAT), C/2002 X5 (Kudo-Fujikawa), C/2002 Y1 (Juels-Holvorcem), 69P/Taylor, and the Relationships among Grain Temperature, Silicate Band Strength and Structure among Comet Families

We report 3 - 13 micron spectroscopy of 4 comets observed between August 2002 and February 2003: C/2002 O4 (Honig) on August 1, 2002, C/2002 V1 (NEAT) on Jan. 9 and 10, 2003, C/2002 X5 (Kudo-Fujikawa) on Jan. 9 and 10, 2003, and C/2002 Y1 (Juels-Holvorcem) on Feb. 20, 2003. In addition, we include data obtained much earlier on 69P/Taylor (February 9, 1998) but not previously published. For Comets Taylor, Honig, NEAT, and Kudo-Fujikawa, the silicate emission band was detected, being approximately 23%, 12%, 15%, and 10%, respectively, above the continuum. The data for Comet Juels-Holvorcem were of insufficient quality to detect the presence of a silicate band of comparable strength to the other three objects, and we place an upper limit of 24% on this feature. The silicate features in both NEAT and Kudo-Fujikawa contained structure indicating the presence of crystalline material. Combining these data with those of other comets, we confirm the correlation between silicate band strength and grain temperature of Gehrz & Ney (1992) and Williams et al. (1997) for dynamically new and long period comets, but the majority of Jupiter family objects may deviate from this relation. The limited data available on Jupiter family objects suggest that they may have silicate bands that are slightly different from the former objects. Finally, when compared to the silicate emission bands observed in pre-main sequence stars, the dynamically new and long period comets most closely resemble the more evolved stellar systems, while the limited data (in quantity and quality) on Jupiter family objects seem to suggest that these have spectra more like the less-evolved stars.Comment: 45 pages, 12 figure

Multi-instrument Evaluation of a Real-time PCR Assay for Identification of Atlantic Salmon: A Case Study on the Use of a Pre-packaged Kit for Rapid Seafood Species Identification

Protecting the seafood supply chain from species substitution is critical for economic, health, and conservation reasons. DNA-based methods represent an effective means to detect species substitution, but current methods can be time consuming or costly, and require specialized instruments and operators. Real-time PCR provides an alternative that can be performed quickly, and in some cases even on-site. The use of commercial kits reduces the expertise required by the operator and therefore increases accessibility to testing. This potentially increases the likelihood of adoption into the supply chain, but only if the kits are robust across multiple operators, instruments, and samples. In this study, the InstantID™ Atlantic salmon kits were tested on a variety of instruments with market samples of fresh, frozen, smoked, and canned Atlantic salmon. Results were repeatable across all samples and instruments tested. This kit, and others like it that have undergone appropriate evaluation, represents a means for expanded access to testing for industry or regulators to screen seafood for species authenticity. Portable equipment can bring testing on-site, further reducing analysis time

Two different evolutionary types of comets proved by polarimetric and infrared properties of their dust

Comets can be divided into two groups: type I, characterized by high gas/dust ratio, low polarization, and a weak or absent 10 micron silicate feature, and type II, for which a low gas/dust ratio, high polarization, and strong silicate feature are typical. We show that the low polarization is the apparent result of depolarization by gas contamination at low dust concentration, which, in turn, results from the dust in type I comets being concentrated near the nucleus. The simulations of thermal emission show that for more porous particles (BCCA), the silicate feature is more pronounced than more compact ones (BPCA), for which it even vanishes as the particles become larger. We also show that in both types of comets the main contribution to light scattering and emission comes from particles larger than 10 micron. Conclusions: .The strength of the silicate feature in the cometary infrared spectra suggests that the dust in type II comets consists of high-porosity aggregates, whereas the dust of type I comets contains low-porosity ones. This is consistent with the polarimetric features of these comets, which indicate that the dust in type I comets tends to concentrate near the nucleus. This may result from the predominance of highly processed particles in type I comets, whereas in type II comets we see pristine or slightly-processed dust. This conclusion is in accordance with the orbital characteristics of the comets. We have found that the strength of the silicate feature correlates with the semi-major axis of periodic comets and, for short-period comets, with the perihelion distance. Thus, the silicate feature weakens due to compaction of aggregate particles if a comet spends more time in the vicinity of the Sun, which allows the comet to accumulate a mantle on the surface of its nucleus

DNA Analysis of Traded Shark Fins and Mobulid Gill Plates Reveals a High Proportion of Species of Conservation Concern

Continuously increasing demand for plant and animal products causes unsustainable depletion of biological resources. It is estimated that one-quarter of sharks and rays are threatened worldwide and although the global fin trade is widely recognized as a major driver, demand for meat, liver oil, and gill plates also represents a significant threat. This study used DNA barcoding and 16 S rRNA sequencing as a method to identify shark and ray species from dried fins and gill plates, obtained in Canada, China, and Sri Lanka. 129 fins and gill plates were analysed and searches on BOLD produced matches to 20 species of sharks and five species of rays or – in two cases – to a species pair. Twelve of the species found are listed or have been approved for listing in 2017 in the appendices of the Convention on International Trade in Endangered Species of Fauna and Flora (CITES), including the whale shark (Rhincodon typus), which was surprisingly found among both shark fin and gill plate samples. More than half of identified species fall under the IUCN Red List categories ‘Endangered’ and ‘Vulnerable’, raising further concerns about the impacts of this trade on the sustainability of these low productivity species

Modelling polarization properties of comet 1P/Halley using a mixture of compact and aggregate particles

Recently, the result obtained from `Stardust' mission suggests that the overall ratio of compact to aggregate particles is 65:35 (or 13:7) for Comet 81P/Wild 2 (Burchell et al. 2008). In the present work, we propose a model which considers cometary dust as a mixture of compact and aggregate particles, with composition of silicate and organic. We consider compact particles as spheroidal particles and aggregates as BCCA and BAM2 aggregate with some size distribution. For modeling Comet 1P/ Halley, the power-law size distribution n(a)= a^{-2.6}, for both compact and aggregate particles is taken. We take a mixture of BAM2 and BCCA aggregates with a lower and upper cutoff size around 0.20$\mu m$ and 1$\mu m$. We also take a mixture of prolate, spherical and oblate compact particles with axial ratio (E) from 0.8 to 1.2 where a lower and upper cutoff size around 0.1$\mu m$ and 10$\mu m$ are taken. Using T-matrix code, the average simulated polarization curves are generated which can best fit the observed polarization data at the four wavelengths $\lambda$ = 0.365$\mu m$, 0.485$\mu m$, 0.670$\mu m$ and 0.684$\mu m$. The suitable mixing percentage of aggregates emerging out from the present modeling corresponds to 50% BAM2 and 50% BCCA particles and silicate to organic mixing percentage corresponds to 78% silicate and 22% organic in terms of volume. The present model successfully reproduces the observed polarization data, especially the negative branch, more effectively as compared to other work done in the past. It is found that among the aggregates, the BAM2 aggregate plays a major role, in deciding the cross-over angle and depth of negative polarization branch.Comment: 7 pages, 5 figures (accepted for publication in MNRAS on May 4, 2011

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

Broadband infrared photometry of comet Hale-Bopp with ISOPHOT

Comet Hale-Bopp was observed five times with ISOPHOT, the photometer on board ESA's Infrared Space Observatory (ISO) between 4.6 and 2.8 AU. Each time, broadband photometry was performed using 4 different detectors, 5 apertures and 10 filters covering the range between 3.6 and 170 μm. Background observations were performed with identical instrument settings at the same positions on the sky several days after the comet observations. The observation strategy and the data reduction steps are described in some detail, including the techniques to correct for variable detector responsivity. The resulting inband power values of the Hale-Bopp observations and their uncertainties are given. The mean uncertainty is 25%. The final fluxes were computed, taking into account the zodiacal background, possible offset of the comet's position from the center of the aperture, the brightness distribution within the coma, and the spectral energy distribution of the comet's emission. Strong thermal emission from a broad size distribution of dust particles was detected in all of the data sets, even at r = 4.6-4.9 AU pre-perihelion and 3.9 AU post-perihelion; the total thermal energy varied as r-3. The 7.3-12.8 μm color temperature was ~1.5 times the blackbody temperature, higher than that observed in any other comet. Silicate features at 10 and 25 μm were prominent in all 5 data sets, the largest heliocentric distances that silicate emission has been detected in a comet. The presence of crystalline water ice grains is suggested from the 60 μm excess emission at 4.6-4.9 AU, consistent with the observed QOH if the icy grains were slightly warmer than an equilibrium blackbody. The average albedo of the dust is higher than that of comet P/Halley, but lower than other albedo measurements for Hale-Bopp nearer perihelion. There is no evidence for a component of cold, bright icy grains enhancing the scattered light at 4.6 AU. Simple models for a mixture of silicate and absorbing grains were fit to the ISO spectra and photometry at 2.8 AU. The observed flux at λ >100 μm requires a size distribution in which most of the mass is concentrated in large particles. Dust production rates of order 1.5 x 105 kg s-1 at 2.8 AU and 3 x 104 kg s-1 at 4.6 AU have been found. They correspond to dust to gas mass ratios of 6 to 10