5,106 research outputs found
The Surface of 2003 EL_(61) in the Near-Infrared
We report the detection of crystalline water ice on the surface of 2003 EL_(61). Reflectance spectra were collected from the Gemini North telescope in the 1.0 to 2.4 μm wavelength range and from the Keck telescope across the 1.4-2.4 μm wavelength range. The signature of crystalline water ice is obvious in all data collected. Like the surfaces of many outer solar system bodies, the surface of 2003 EL_(61) is rich in crystalline water ice, which is energetically less favored than amorphous water ice at low temperatures, suggesting that resurfacing processes may be taking place. The near-infrared color of the object is much bluer than a pure water ice model. Adding a near-infrared blue component such as hydrogen cyanide or phyllosilicate clays improves the fit considerably, with hydrogen cyanide providing the greatest improvement. The addition of hydrated tholins and bitumens also improves the fit, but is inconsistent with the neutral V - J reflectance of 2003 EL_(61). A small decrease in reflectance beyond 2.3 μm may be attributable to cyanide salts. Overall, the reflected light from 2003 EL_(61) is best fit by a model of 2/3-4/5 pure crystalline water ice and 1/3-1/5 near-infrared blue component such as hydrogen cyanide or kaolinite. The surface of 2003 EL_(61) is unlikely to be covered by significant amounts of dark material such as carbon black, as our pure ice models reproduce published albedo estimates derived from the spin state of 2003 EL_(61)
Near Infrared Surface Properties of the Two Intrinsically Brightest Minor Planets (90377) Sedna and (90482) Orcus
We present low resolution K band spectra taken at the Gemini 8 meter
telescope of (90377) Sedna and (90482) Orcus (provisional designations 2003
VB12 and 2004 DW, respectively), currently the two minor planets with the
greatest absolute magnitudes (i.e. the two most reflective minor planets). We
place crude limits on the surface composition of these two bodies using a Hapke
model for a wide variety of assumed albedos. The unusual minor planet (90377)
Sedna was discovered on November 14, 2003 UT at roughly 90 AU with 1.6 times
the heliocentric distance and perihelion distance of any other bound minor
planet. It is the first solar system object discovered between the Kuiper Belt
and the Oort Cloud, and may represent a transition population between the two.
The reflectance spectrum of (90377) Sedna appears largely featureless at the
current signal-to-noise ratio, suggesting a surface likely to be highly
processed by cosmic rays. For large grain models (100 micron to 1 cm) we find
that (90377) Sedna must have less than 70% surface fraction of water ice and
less than 60% surface fraction of methane ice to 3 sigma confidence. Minor
planet (90482) Orcus shows strong water ice absorption corresponding to less
than 50% surface fraction for grain models 25 micron and larger. Orcus cannot
have more than 30% of its surface covered by large (100 mm to 1 cm) methane
grains to 3 sigma confidence.Comment: Accepted for publication in the Astrophysical Journa
Invasive Signal Crayfish in the UK: Survey Methods to Inform Evidence-based Management
With invasive crayfish becoming increasingly widespread, evidence-based management is crucial to
protect freshwater ecosystems. Knowledge of the structure and function of invasive crayfish
populations allows for an effective evaluation of management efforts. Recent methodological
developments have enabled the first truly quantitative studies of UK invasive crayfish populations in
the field. This was achieved by the ‘triple drawdown’ (TDD) survey approach. In this article, we
explore current survey approaches and their limitations, and we introduce the TDD method with its
implications for crayfish survey, policy development and management
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