577 research outputs found
Hazy Blue Worlds:A Holistic Aerosol Model for Uranus and Neptune, Including Dark Spots
We present a reanalysis (using the Minnaert limb-darkening approximation) of
visible/near-infrared (0.3 - 2.5 micron) observations of Uranus and Neptune
made by several instruments. We find a common model of the vertical aerosol
distribution that is consistent with the observed reflectivity spectra of both
planets, consisting of: 1) a deep aerosol layer with a base pressure > 5-7 bar,
assumed to be composed of a mixture of H2S ice and photochemical haze; 2) a
layer of photochemical haze/ice, coincident with a layer of high static
stability at the methane condensation level at 1-2 bar; and 3) an extended
layer of photochemical haze, likely mostly of the same composition as the
1-2-bar layer, extending from this level up through to the stratosphere, where
the photochemical haze particles are thought to be produced. For Neptune, we
find that we also need to add a thin layer of micron-sized methane ice
particles at ~0.2 bar to explain the enhanced reflection at longer
methane-absorbing wavelengths. We suggest that methane condensing onto the haze
particles at the base of the 1-2-bar aerosol layer forms ice/haze particles
that grow very quickly to large size and immediately 'snow out' (as predicted
by Carlson et al. 1988), re-evaporating at deeper levels to release their core
haze particles to act as condensation nuclei for H2S ice formation. In
addition, we find that the spectral characteristics of 'dark spots', such as
the Voyager-2/ISS Great Dark Spot and the HST/WFC3 NDS-2018, are well modelled
by a darkening or possibly clearing of the deep aerosol layer only.Comment: 58 pages, 23 figures, 4 table
Hazy Blue Worlds:A Holistic Aerosol Model for Uranus and Neptune, Including Dark Spots
We present a reanalysis (using the Minnaert limb-darkening approximation) of
visible/near-infrared (0.3 - 2.5 micron) observations of Uranus and Neptune
made by several instruments. We find a common model of the vertical aerosol
distribution that is consistent with the observed reflectivity spectra of both
planets, consisting of: 1) a deep aerosol layer with a base pressure > 5-7 bar,
assumed to be composed of a mixture of H2S ice and photochemical haze; 2) a
layer of photochemical haze/ice, coincident with a layer of high static
stability at the methane condensation level at 1-2 bar; and 3) an extended
layer of photochemical haze, likely mostly of the same composition as the
1-2-bar layer, extending from this level up through to the stratosphere, where
the photochemical haze particles are thought to be produced. For Neptune, we
find that we also need to add a thin layer of micron-sized methane ice
particles at ~0.2 bar to explain the enhanced reflection at longer
methane-absorbing wavelengths. We suggest that methane condensing onto the haze
particles at the base of the 1-2-bar aerosol layer forms ice/haze particles
that grow very quickly to large size and immediately 'snow out' (as predicted
by Carlson et al. 1988), re-evaporating at deeper levels to release their core
haze particles to act as condensation nuclei for H2S ice formation. In
addition, we find that the spectral characteristics of 'dark spots', such as
the Voyager-2/ISS Great Dark Spot and the HST/WFC3 NDS-2018, are well modelled
by a darkening or possibly clearing of the deep aerosol layer only.Comment: 58 pages, 23 figures, 4 table
Spectral determination of the colour and vertical structure of dark spots in Neptune's atmosphere
Previous observations of dark vortices in Neptune's atmosphere, such as
Voyager-2's Great Dark Spot, have been made in only a few, broad-wavelength
channels, which has hampered efforts to pinpoint their pressure level and what
makes them dark. Here, we present Very Large Telescope (Chile) MUSE
spectrometer observations of Hubble Space Telescope's NDS-2018 dark spot, made
in 2019. These medium-resolution 475 - 933 nm reflection spectra allow us to
show that dark spots are caused by a darkening at short wavelengths (< 700 nm)
of a deep ~5-bar aerosol layer, which we suggest is the HS condensation
layer. A deep bright spot, named DBS-2019, is also visible on the edge of
NDS-2018, whose spectral signature is consistent with a brightening of the same
5-bar layer at longer wavelengths (> 700 nm). This bright feature is much
deeper than previously studied dark spot companion clouds and may be connected
with the circulation that generates and sustains such spots.Comment: 1 table. 3 figures. Nature Astronomy (2023
Spectral determination of the colour and vertical structure of dark spots in Neptune’s atmosphere
Previous observations of dark vortices in Neptune’s atmosphere, such as Voyager 2’s Great Dark Spot (1989), have been made in only a few broad-wavelength channels, hampering efforts to determine these vortices’ pressure levels and darkening processes. We analyse spectroscopic observations of a dark spot on Neptune identified by the Hubble Space Telescope as NDS-2018; the spectral observations were made in 2019 by the Multi Unit Spectroscopic Explorer (MUSE) of the Very Large Telescope (Chile). The MUSE medium-resolution 475–933 nm reflection spectra allow us to show that dark spots are caused by darkening at short wavelengths (700 nm). This bright feature is much deeper than previously studied dark-spot companion clouds and may be connected with the circulation that generates and sustains such spots
Recent Estimates of Ring-Tailed Lemur (Lemur catta) Population Declines are Methodologically Flawed and Misleading
Recent Estimates of Ring-Tailed Lemur (Lemur catta) Population Declines are Methodologically Flawed and Misleading
Better Few than Hungry: Flexible Feeding Ecology of Collared Lemurs Eulemur collaris in Littoral Forest Fragments
Frugivorous primates are known to encounter many problems to cope with habitat degradation, due to the fluctuating spatial and temporal distribution of their food resources. Since lemur communities evolved strategies to deal with periods of food scarcity, these primates are expected to be naturally adapted to fluctuating ecological conditions and to tolerate a certain degree of habitat changes. However, behavioral and ecological strategies adopted by frugivorous lemurs to survive in secondary habitats have been little investigated. Here, we compared the behavioral ecology of collared lemurs (Eulemur collaris) in a degraded fragment of littoral forest of south-east Madagascar, Mandena, with that of their conspecifics in a more intact habitat, Sainte Luce.Lemur groups in Mandena and in Sainte Luce were censused in 2004/2007 and in 2000, respectively. Data were collected via instantaneous sampling on five lemur groups totaling 1,698 observation hours. The Shannon index was used to determine dietary diversity and nutritional analyses were conducted to assess food quality. All feeding trees were identified and measured, and ranging areas determined via the minimum convex polygon. In the degraded area lemurs were able to modify several aspects of their feeding strategies by decreasing group size and by increasing feeding time, ranging areas, and number of feeding trees. The above strategies were apparently able to counteract a clear reduction in both food quality and size of feeding trees.Our findings indicate that collared lemurs in littoral forest fragments modified their behavior to cope with the pressures of fluctuating resource availability. The observed flexibility is likely to be an adaptation to Malagasy rainforests, which are known to undergo periods of fruit scarcity and low productivity. These results should be carefully considered when relocating lemurs or when selecting suitable areas for their conservation
Ancient hydrothermal seafloor deposits in Eridania basin on Mars
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/ licenses/by/4.0/. The file attached is the Published/publisher’s pdf version of the article
Long-term field studies of lemurs, lorises, and tarsiers
Lemurs, lorises, and tarsiers are socially and ecologically diverse primates that include some of the most endangered mammals. We review results of long-term studies of 15 lemur species from 7 sites in Madagascar and 1 species each of loris and tarsier in Indonesia. We emphasize that the existence of long-term study populations is a crucial prerequisite for planning and conducting shorter studies on specific topics, as exemplified by various ecophysiological studies of lemurs. Extended studies of known individuals have revealed variation in social organization within and between ecologically similar species. Even for these primates with relatively fast life histories, it required more than a decade of paternity data to characterize male reproductive skew. The long-term consequences of female rank on reproductive success remain poorly known, however. Long-term monitoring of known individuals is the only method to obtain data on life-history adaptations, which appear to be shaped by predation in the species covered here; long-term studies are also needed for addressing particular questions in community ecology. The mere presence of long-term projects has a positive effect on the protection of study sites, and they generate unique data that are fundamental to conservation measures, such as close monitoring of populations.
Los lémures, lorises y tarseros son grupos de primates, muy diversos social y ecológicamente, que incluyen algunas de las especies de mamÃferos más amenazadas. Se revisaron los resultados de estudios a largo plazo de 15 especies de lémures en 7 áreas de estudio en Madagascar y una especie de loris y otra de tarsero, en Indonesia. Se resalta la importancia de las áreas de estudio a largo plazo como prerrequisito esencial para planear y llevar a cabo estudios de menor duración sobre temas especificos, como lo ejemplifican varios estudios eco-fisiológicos en lemurs. Estudios a largo plazo de individuos conocidos, han revelado variacion en la organizacion social dentro y entre especies ecologicamente similares. Incluso en estos primates, con un ciclo de vida relativamente corto, se necesita recopilar más de una década de datos de paternidad para determinar el sesgo reproductivo de los machos. Sin embargo, aún se sabe poco de las consecuencias a largo plazo que la posición de las hembras en la jerarquÃa social puede tener en su éxito reproductivo. El monitoreo a largo plazo de individuos conocidos es el unico metodo para obtener datos sobre adaptaciones en su history natural, las cuales aparentemente son moduladas en function de la predacion a las especies estudiadas en este trabajo. Estos estudios a largo plazo son tambien necesarios para afrontar temas especÃficos sobre la ecologÃa de estas comunidades. La simple presencia de proyectos a largo plazo tienen un efecto positive en la proteccion de los lugares de studio, como asi tambien generan datos unicos que son fundamentals para apoyar medidas de conservacion tales como el monitoreo de poblaciones
- …