156 research outputs found
Planetary mass-radius relations across the galaxy
Planet formation theory suggests that planet bulk compositions are likely to
reflect the chemical abundance ratios of their host star's photosphere.
Variations in the abundance of particular chemical species in stellar
photospheres between different galactic stellar populations demonstrate that
there are differences among the expected solid planet bulk compositions. We aim
to present planetary mass-radius relations of solid planets for kinematically
differentiated stellar populations, namely, the thin disc, thick disc, and
halo. Using two separate internal structure models, we generated synthetic
planets using bulk composition inputs derived from stellar abundances. We
explored two scenarios, specifically iron-silicate planets at 0.1 AU and
silicate-iron-water planets at 4 AU. We show that there is a persistent
statistical difference in the expected mass-radius relations of solid planets
among the different galactic stellar populations. At 0.1 AU for silicate-iron
planets, there is a 1.51 to 2.04\% mean planetary radius difference between the
thick and thin disc stellar populations, whilst for silicate-iron-water planets
past the ice line at 4 AU, we calculate a 2.93 to 3.26\% difference depending
on the models. Between the halo and thick disc, we retrieve at 0.1 AU a 0.53 to
0.69\% mean planetary radius difference, and at 4 AU we find a 1.24 to 1.49\%
difference depending on the model. Future telescopes (such as PLATO) will be
able to precisely characterize solid exoplanets and demonstrate the possible
existence of planetary mass-radius relationship variability between galactic
stellar populations.Comment: 11 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
The clinical value of [90Y-DOTA]-D-Phe1-Tyr3-octreotide (90Y-DOTATOC) in the treatment of neuroendocrine tumours: A clinical phase II study
Purpose: The aim of this phase II study was to evaluate the tumour response of neuroendocrine tumours to targeted irradiation with the radiolabelled somatostatin analogue 90Y-DOTATOC. In addition, the palliative effect of 90-Y-DO-TATOC treatment on the malignant carcinoid syndrome and tumour-associated pain was investigated. Patients and methods: Forty-one patients (mean age 53 years) with neuroendocrine gastroenteropancreatic and bronchial tumours were included. Eighty-two percent of the patients had therapy resistant and progressive disease. The treatment con sisted of four intravenous injections ofa total of 6000 MBq/m2 90Y-DOTATOC, administered at intervals of six weeks. Results:The overall response rate was 24%. For endocrine pancreatic tumours it was 36%. Complete remissions (CR) were found in 2% (1 of 41), partial remissions (PR) in 22% (9 of 41), minor response in 12% (5 of 41), stable disease (SD) in 49% (20 of4l) and progressive disease (PD) in 15% (6 of4l). The median follow up was 15 months (range 1 month to 36 months). The median duration of response has not been reached at 26 months. The two-year survival time was 76 ± 16%. Eighty-three percent of the patients suffering from the malignant carcinoid syndrome achieved a significant reduction of symptoms. The treatment was well tolerated. A reduction of pain score was observed in all patients (5 of 41) with morphine dependent tumour-associated pain. Side effects included grade LU (NCIGC) pancytopenia in 5%, and vomiting shortly after injection in 23%. No grade III—IV renal toxicity was observed. Conclusion: Targeted radiotherapy with 90Y-DOTATOC is a novel, well-tolerated treatment for neuroendocrine turnours with a remarkable objective response rate, survival time, and symptomatic respons
Impact of the measured parameters of exoplanets on the inferred internal structure
Exoplanet characterization is one of the main foci of current exoplanetary
science. For super-Earths and sub-Neptunes, we mostly rely on mass and radius
measurements, which allow to derive the body's mean density and give a rough
estimate of the planet's bulk composition. However, the determination of
planetary interiors is a very challenging task. In addition to the uncertainty
in the observed fundamental parameters, theoretical models are limited due to
the degeneracy in determining the planetary composition. We aim to study
several aspects that affect internal characterization of super-Earths and
sub-Neptunes: observational uncertainties, location on the M-R diagram, impact
of additional constraints as bulk abundances or irradiation, and model
assumptions. We use a full probabilistic Bayesian inference analysis that
accounts for observational and model uncertainties. We employ a Nested Sampling
scheme to efficiently produce the posterior probability distributions for all
the planetary structural parameter of interest. We include a structural model
based on self-consistent thermodynamics of core, mantle, high-pressure ice,
liquid water, and H-He envelope. Regarding the effect of mass and radius
uncertainties on the determination of the internal structure, we find three
different regimes: below the Earth-like composition line and above the
pure-water composition line smaller observational uncertainties lead to better
determination of the core and atmosphere mass respectively, and between them
structure characterization only weakly depends on the observational
uncertainties. We show that small variations in the temperature or entropy
profiles lead to radius variations that are comparable to the observational
uncertainty, suggesting that uncertainties linked to model assumptions can
become more relevant to determine the internal structure than observational
uncertainties.Comment: 12 pages, 12 figure
Field Studies of Crater Gradation in Gusev Crater and Meridiani Planum Using the Mars Exploration Rovers
The Mars Exploration Rovers Spirit and Opportunity investigated numerous craters since landing in Gusev crater (14.569degS, 175.473degE) and Meridiani Planum (1.946degS, 354.473degE) over the first 400 sols of their missions [1-4]. Craters at both sites are simple structures and vary in size and preservation state. Comparing observed and expected pristine morphology and using process-specific gradational signatures around terrestrial craters as a template [5-7] allows distinguishing gradation processes whose relative importance fundamentally differs from those responsible for most crater modification on the Earth
Correlation of Rock Spectra with Quantitative Morphologic Indices: Evidence for a Single Rock Type at the Mars Pathfinder Landing Site
The Mars Pathfinder (MPF) landing site was predicted to contain a broad sampling of rock types varying in mineralogical, physical, mechanical and geochemical characteristics. Although rocks have been divided into several spectral categories based on Imager for Mars Pathfinder (IMP) visible/near-infrared data, efforts in isolating and classifying spectral units among MPF rocks and soils have met with varying degrees of success, as many factors influencing spectral signatures cannot be quantified to a sufficient level to be removed. It has not been fully determined which spectral categories stem from intrinsic mineralogical differences between rocks or rock surfaces, and which result from factors such as physical or chemical weathering. This has made isolation of unique rock mineralogies difficult. Morphology, like composition, is a characteristic tied to the intrinsic properties and geologic and weathering history of rocks. Rock morphologies can be assessed quantitatively and compared with spectral data, to identify and classify rock types at the MPF landing site. They can also isolate actual rock spectra from spectral types that are surficial in origin, as compositions associated with mantling dust or chemical coatings would presumably not influence rock morphology during weathering events. We previously reported on an initial classification of rocks using the quantitative morphologic indices of size, roundness, sphericity and elongation. Here, we compare this database of rock characteristics with associated rock surface spectra to improve our ability to discriminate between spectra associated with rock types and those from other sources
The Nominal Range of Rocky Planet Masses, Radii, Surface Gravities and Bulk Densities
The two primary observable quantities of an exoplanet--its mass and
radius--alone are not sufficient to probe a rocky exoplanet's interior
composition and mineralogy. To overcome this, host-star abundances of the
primary planet-building elements (Mg, Si, Fe) are typically used as a proxy for
the planet's bulk composition. The majority of small exoplanet hosts, however,
do not have available abundance data. Here we present the open-source ExoPlex
mass-radius-composition solver. Unlike previous open-source mass-radius
solvers, ExoPlex calculates the core chemistry and equilibrium mantle
mineralogy for a bulk composition, including effects of mantle FeO content,
core light elements and surface water/ice. We utilize ExoPlex to calculate the
planetary radii, surface gravities and bulk densities for 10 model planets
up to 2 R across these geochemistries, adopting the distribution of
FGK stellar abundances to estimate of the range of bulk exoplanet compositions.
We outline the distribution of radii, surface gravity and bulk
densities that define planets as "nominally rocky." Planets outside this range
require compositions outside those expected from stellar abundance data, likely
making them either Fe-enriched super-Mercuries, or volatile-enriched
mini-Neptunes. We apply our classification scheme to a sample of 85
well-resolved exoplanets without available host-star abundances. We estimate
only 9 planets are within the "nominally rocky planet zone" at
confidence, while and of this sample can be reasonably
classified as super-Mercuries or volatile-rich, respectively. Our results
provide observers with a self-consistent way to broadly classify a planet as
likely rocky, Mercury-like or volatile-enriched, using mass and radius
measurements alone.Comment: 41 pages, 21 figures, 2 tables. Accepted to Ap
Volatiles in the Desert: Subtle Remote-sensing Signatures of the Dakhleh Oasis Catastrophic Event, Western Desert, Egypt
Over the past decade members of the Dakhleh Oasis Project have studied enigmatic signatures in the Pleistocene geologic record of portions of the Dakhleh oasis and palaeo-oasis in Egypt's Western Desert [1,2]. In particular, Si-Ca-Al rich glass melt (Dakhleh Glass, Fig. 1) points to a catastrophic event between c.100,000-200,000 years ago [3] in this well-studied African savannah and freshwater lake Middle Stone Age environment [4,5]
Uncertainty analysis of the use of a retailer fidelity card scheme in the assessment of food additive intake
International audienceThe feasibility of using a retailer fidelity card scheme to estimate food additive intake has been investigated in an earlier study. Fidelity card survey information was combined with information provided by the retailer on levels of the food colour Sunset Yellow (E110) in the foods to estimate a daily exposure to the additive in the Swiss population. As with any dietary exposure method the fidelity card scheme is subject to uncertainties and in this paper the impact of uncertainties associated with input variables including amounts of food purchased, levels of E110 in food, proportion of food purchased at retailer, rate of fidelity card usage, proportion of foods consumed outside of home and bodyweights and with systematic uncertainties has been assessed using a qualitative, deterministic and probabilistic approach. An analysis of the sensitivity of the results to each of the probabilistic inputs was also undertaken. The analysis was able to identify the key factors responsible for uncertainty within the model and demonstrate how the application of some simple probabilistic approaches can be used to quantitatively assess uncertainty
Crater gradation in Gusev crater and Meridiani Planum, Mars
The Mars Exploration Rovers investigated numerous craters in Gusev crater and Meridiani Planum during the first ∼400 sols of their missions. Craters vary in size and preservation state but are mostly due to secondary impacts at Gusev and primary impacts at Meridiani. Craters at both locations are modified primarily by eolian erosion and infilling and lack evidence for modification by aqueous processes. Effects of gradation on crater form are dependent on size, local lithology, slopes, and availability of mobile sediments. At Gusev, impacts into basaltic rubble create shallow craters and ejecta composed of resistant rocks. Ejecta initially experience eolian stripping, which becomes weathering-limited as lags develop on ejecta surfaces and sediments are trapped within craters. Subsequent eolian gradation depends on the slow production of fines by weathering and impacts and is accompanied by minor mass wasting. At Meridiani the sulfate-rich bedrock is more susceptible to eolian erosion, and exposed crater rims, walls, and ejecta are eroded, while lower interiors and low-relief surfaces are increasingly infilled and buried by mostly basaltic sediments. Eolian processes outpace early mass wasting, often produce meters of erosion, and mantle some surfaces. Some small craters were likely completely eroded/buried. Craters \u3e100 m in diameter on the Hesperian-aged floor of Gusev are generally more pristine than on the Amazonian-aged Meridiani plains. This conclusion contradicts interpretations from orbital views, which do not readily distinguish crater gradation state at Meridiani and reveal apparently subdued crater forms at Gusev that may suggest more gradation than has occurred
Refining the transit-timing and photometric analysis of TRAPPIST-1: Masses, Radii, densities, dynamics, and ephemerides
We have collected transit times for the TRAPPIST-1 system with the Spitzer
Space Telescope over four years. We add to these ground-based, HST and K2
transit time measurements, and revisit an N-body dynamical analysis of the
seven-planet system using our complete set of times from which we refine the
mass ratios of the planets to the star. We next carry out a photodynamical
analysis of the Spitzer light curves to derive the density of the host star and
the planet densities. We find that all seven planets' densities may be
described with a single rocky mass-radius relation which is depleted in iron
relative to Earth, with Fe 21 wt% versus 32 wt% for Earth, and otherwise
Earth-like in composition. Alternatively, the planets may have an Earth-like
composition, but enhanced in light elements, such as a surface water layer or a
core-free structure with oxidized iron in the mantle. We measure planet masses
to a precision of 3-5%, equivalent to a radial-velocity (RV) precision of 2.5
cm/sec, or two orders of magnitude more precise than current RV capabilities.
We find the eccentricities of the planets are very small; the orbits are
extremely coplanar; and the system is stable on 10 Myr timescales. We find
evidence of infrequent timing outliers which we cannot explain with an eighth
planet; we instead account for the outliers using a robust likelihood function.
We forecast JWST timing observations, and speculate on possible implications of
the planet densities for the formation, migration and evolution of the planet
system
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