4,181 research outputs found
The Orbit of Transneptunian Binary Manw\"e and Thorondor and their Upcoming Mutual Events
A new Hubble Space Telescope observation of the 7:4 resonant transneptunian
binary system (385446) Manw\"e has shown that, of two previously reported
solutions for the orbit of its satellite Thorondor, the prograde one is
correct. The orbit has a period of 110.18 0.02 days, semimajor axis of
6670 40 km, and an eccentricity of 0.563 0.007. It will be viewable
edge-on from the inner solar system during 2015-2017, presenting opportunities
to observe mutual occultation and eclipse events. However, the number of
observable events will be small, owing to the long orbital period and expected
small sizes of the bodies relative to their separation. This paper presents
predictions for events observable from Earth-based telescopes and discusses the
associated uncertainties and challenges.Comment: 15 pages, 3 figures, 5 table
Selective advantage of implementing optimal contributions selection and timescales for the convergence of long-term genetic contributions
Additional file 1: Figure S1. Accumulation of long-term genetic contributions over time with a line of best fit
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A study protocol for a randomised crossover study evaluating the effect of diets differing in carbohydrate quality on ileal content and appetite regulation in healthy humans
A major component of the digesta reaching the colon from the distal ileum is carbohydrate. This carbohydrate is subject to microbial fermentation and can radically change bacterial populations in the colon and the metabolites they produce, particularly short-chain fatty acids (SCFA). However, very little is currently known about the forms and levels of carbohydrate in the ileum and the composition of the ileal microbiota in humans. Most of our current understanding of carbohydrate that is not absorbed by the small intestine comes from ileostomy models, which may not reflect the physiology of an intact gastrointestinal tract. We will investigate how ileal content changes depending on diet using a randomised crossover study in healthy humans. Participants will be inpatients at the research facility for three separate 4-day visits. During each visit, participants will consume one of three diets, which differ in carbohydrate quality: 1) low-fibre refined diet; 2) high-fibre diet with intact cellular structures; 3) high-fibre diet where the cellular structures have been disrupted (e.g. milling, blending). On day 1, a nasoenteric tube will be placed into the distal ileum and its position confirmed under fluoroscopy. Ileal samples will be collected via the nasoenteric tube and metabolically profiled, which will determine the amount and type of carbohydrate present, and the composition of the ileal microbiota will be measured. Blood samples will be collected to assess circulating hormones and metabolites. Stool samples will be collected to assess faecal microbiota composition. Subjective appetite measures will be collected using visual analogue scales. Breath hydrogen will be measured in real-time as a marker of intestinal fermentation. Finally, an continuous fermentation model will be inoculated with ileal fluid in order to understand the shift in microbial composition and SCFA produced in the colon following the different diets. ISRCTN11327221. [Abstract copyright: Copyright: © 2019 Byrne CS et al.
Ice mineralogy across and into the surfaces of Pluto, Triton, and Eris
We present three near-infrared spectra of Pluto taken with the Infrared Telescope Facility and SpeX, an optical spectrum of Triton taken with the MMT and the Red Channel Spectrograph, and previously published spectra of Pluto, Triton, and Eris. We combine these observations with a two-phase Hapke model and gain insight into the ice mineralogy on Pluto, Triton, and Eris. Specifically, we measure the methane-nitrogen mixing ratio across and into the surfaces of these icy dwarf planets. In addition, we present a laboratory experiment that demonstrates it is essential to model methane bands in spectra of icy dwarf planets with two methane phases—one highly diluted by nitrogen and the other rich in methane. For Pluto, we find bulk, hemisphere-averaged, methane abundances of 9.1% ± 0.5%, 7.1% ± 0.4%, and 8.2% ± 0.3% for sub-Earth longitudes of 10°, 125°, and 257°. Application of the Wilcoxon rank sum test to our measurements finds these small differences are statistically significant. For Triton, we find bulk, hemisphere-averaged, methane abundances of 5.0% ± 0.1% and 5.3% ± 0.4% for sub-Earth longitudes of 138° and 314°. Application of the Wilcoxon rank sum test to our measurements finds the differences are not statistically significant. For Eris, we find a bulk, hemisphere-averaged, methane abundance of 10% ± 2%. Pluto, Triton, and Eris do not exhibit a trend in methane-nitrogen mixing ratio with depth into their surfaces over the few centimeter range probed by these observations. This result is contrary to the expectation that since visible light penetrates deeper into a nitrogen-rich surface than the depths from which thermal emission emerges, net radiative heating at depth would drive preferential sublimation of nitrogen leading to an increase in the methane abundance with depth
Pluto's global surface composition through pixel-by-pixel Hapke modeling of New Horizons Ralph/LEISA data
On July 14th 2015, NASA's New Horizons mission gave us an unprecedented
detailed view of the Pluto system. The complex compositional diversity of
Pluto's encounter hemisphere was revealed by the Ralph/LEISA infrared
spectrometer on board of New Horizons. We present compositional maps of Pluto
defining the spatial distribution of the abundance and textural properties of
the volatiles methane and nitrogen ices and non-volatiles water ice and tholin.
These results are obtained by applying a pixel-by-pixel Hapke radiative
transfer model to the LEISA scans. Our analysis focuses mainly on the large
scale latitudinal variations of methane and nitrogen ices and aims at setting
observational constraints to volatile transport models. Specifically, we find
three latitudinal bands: the first, enriched in methane, extends from the pole
to 55deg N, the second dominated by nitrogen, continues south to 35deg N, and
the third, composed again mainly of methane, reaches 20deg N. We demonstrate
that the distribution of volatiles across these surface units can be explained
by differences in insolation over the past few decades. The latitudinal pattern
is broken by Sputnik Planitia, a large reservoir of volatiles, with nitrogen
playing the most important role. The physical properties of methane and
nitrogen in this region are suggestive of the presence of a cold trap or
possible volatile stratification. Furthermore our modeling results point to a
possible sublimation transport of nitrogen from the northwest edge of Sputnik
Planitia toward the south.Comment: 43 pages, 7 figures; accepted for publication in Icaru
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