Hyla versicolor-chrysoscelis Species Complex of Gray Treefrogs in Arkansas: Histological and Ultrastructural evidence

We investigated the Hyla versicolor-chrysoscelis species complex (tetraploid and diploid species, respectively) of cryptic gray treefrogs from Arkansas using light and scanning electron microscopy. From previous studies of this treefrog complex in other states, H. versicolor has been shown to exhibit larger nuclear diameters and larger toe pad epithelial cells than H. chrysoscelis. Based upon average nuclear diameters of eyelid epithelial cells, we found two or possibly three groups of frogs. The presumed H. versicolor exhibited greatly enlarged toe pad epithelial cells using scanning electron microscopy and were found in four counties, three of which are in the Ozark Mountains. Hyla chrysoscelis occurs throughout the stat

Magnetospheric processes mediate atmospheric escape at Earth, Mars, and Venus: key open questions demand renewed Venus exploration

International audienceEarth, Mars, and Venus span a range of magnetosphere configurations, from the global/intrinsic dipole field of Earth, through the hybrid crustal field and induced magnetosphere of Mars, to the wholly induced magnetosphere of Venus. These differences in intrinsic field strength and geometry lead to differences in the processes driving atmospheric escape from each planet to space, which may in turn have led to the different evolutionary trajectories and vastly different habitability of these planets. Multiple missions at Earth and Mars have fostered a detailed understanding of their atmospheric escape mechanisms. While gaps remain, this understanding is more developed than that at Venus, which exhibits several characteristics that make it an ideal laboratory to observe the coupling between magnetosphere processes and escape. First, a combination of high Earth-like gravity and low Mars-like thermosphere temperatures suppresses thermal H escape at Venus, uniquely enabling the investigation of nonthermal ion-driven photochemical escape and direct ion escape processes, which may dominate on Venus-like exoplanets. Second, ion escape processes at Venus are required to remove atmospheric O in order to explain the low atmospheric oxygen abundance, but the existing ion escape measurements by the Pioneer Venus Orbiter and Venus Express leave many details of upward transport and acceleration underexplored. While Venus lacks a global dipole magnetic field, the nightside magnetic field configuration is in some ways similar to the Earth's polar regions and Martian crustal field cusps. Thus, cold light and heavy ion outflow driven by ambipolar electric fields may occur at Venus, in analogy to the "polar wind" hydrogen ion outflow at Earth and heavy ion outflow at Mars. For both ion and neutral escape, variation of solar input on evolutionary timescales and across solar system planets requires a focus on understanding physical processes, so that they can be extrapolated to other times and to exoplanets. As the world’s space agencies turn their eyes toward Venus over the coming decade, the essential role played by the magnetosphere in mediating Venus evolution should not be overlooked: future upper atmosphere measurements at Venus are likely to illuminate magnetosphere-escape coupling processes throughout the cosmos

Magnetospheric processes mediate atmospheric escape at Earth, Mars, and Venus: key open questions demand renewed Venus exploration

International audienceEarth, Mars, and Venus span a range of magnetosphere configurations, from the global/intrinsic dipole field of Earth, through the hybrid crustal field and induced magnetosphere of Mars, to the wholly induced magnetosphere of Venus. These differences in intrinsic field strength and geometry lead to differences in the processes driving atmospheric escape from each planet to space, which may in turn have led to the different evolutionary trajectories and vastly different habitability of these planets. Multiple missions at Earth and Mars have fostered a detailed understanding of their atmospheric escape mechanisms. While gaps remain, this understanding is more developed than that at Venus, which exhibits several characteristics that make it an ideal laboratory to observe the coupling between magnetosphere processes and escape. First, a combination of high Earth-like gravity and low Mars-like thermosphere temperatures suppresses thermal H escape at Venus, uniquely enabling the investigation of nonthermal ion-driven photochemical escape and direct ion escape processes, which may dominate on Venus-like exoplanets. Second, ion escape processes at Venus are required to remove atmospheric O in order to explain the low atmospheric oxygen abundance, but the existing ion escape measurements by the Pioneer Venus Orbiter and Venus Express leave many details of upward transport and acceleration underexplored. While Venus lacks a global dipole magnetic field, the nightside magnetic field configuration is in some ways similar to the Earth's polar regions and Martian crustal field cusps. Thus, cold light and heavy ion outflow driven by ambipolar electric fields may occur at Venus, in analogy to the "polar wind" hydrogen ion outflow at Earth and heavy ion outflow at Mars. For both ion and neutral escape, variation of solar input on evolutionary timescales and across solar system planets requires a focus on understanding physical processes, so that they can be extrapolated to other times and to exoplanets. As the world’s space agencies turn their eyes toward Venus over the coming decade, the essential role played by the magnetosphere in mediating Venus evolution should not be overlooked: future upper atmosphere measurements at Venus are likely to illuminate magnetosphere-escape coupling processes throughout the cosmos

Measurement needs for understanding Venus water evolution

International audienceThe current dry state of Venus indicates that most of its water has been lost to space by a combination of early hydrodynamic and ongoing neutral and ion loss processes. The abundance and HDO/H2O ratio of the remaining water is regulated by hydrogen and deuterium escape to space, but there remains substantial uncertainty in the rate of present-day H loss, the relative importance of neutral H vs. H+ ion escape, and the fractionation factor of this escape. The interpretation of planned lower atmosphere measurements depends critically on these unconstrained upper atmosphere processes. For O and other heavier species, ion loss has likely played a major role, but existing measurements of ion escape are hopelessly separated from measurements of the ion source region by a poorly constrained transport and acceleration region, so that the processes controlling ion loss remain obscure. Further, ion supply, energization and transport, and finally escape are heavily influenced by the incoming flux of extreme ultraviolet photons and related changes in Venus’ external space environment. The substantial variations of these inputs over both solar cycle and geologic timescales, and their effects on key atmospheric processes, have not been sufficiently constrained. These unknowns frustrate the interpretation of lower and middle atmosphere observations, including those planned by future NASA and ESA missions, and inhibit the formulation of a self-consistent history for our sister planet. Here we call for new measurements of the Venus upper atmosphere and ionosphere to resolve these uncertainties and extend the scope of currently funded efforts to cover the entire atmosphere, from surface to space. The required remote sensing and in situ instruments are high-heritage, low mass, and low power, and the required altitude sampling and spatial coverage could be provided by a small spacecraft, yielding a transformative science return at relatively modest cost. A flotilla of space missions brought forth by an international community of scientists will soon visit Venus: upper atmosphere measurements, and the critical contributions they enable, must not be left behind

Desiccation Of Venus Explorer (DOVE): a NASA SIMPLEx mission concept to soar through the skies of Venus and unveil its water history

International audienceVenus is a near-twin of Earth in size and mass, but its current atmosphere is extremely thick, hot, and dry, indicating a remarkably different evolutionary trajectory. Planned NASA and ESA missions will make measurements of Venus surface geology and bulk atmosphere isotope ratios that are critical to reconstruct the history of the planet. However, no currently selected mission will measure processes in the upper atmosphere that directly control the evolution of the planet’s volatile inventory. These processes, which transport volatiles upward and enable their escape, remain underconstrained despite the significant accomplishments of the Pioneer Venus Orbiter and Venus Express missions. Here we present a NASA SIMPLEx mission concept, Desiccation Of Venus Explorer (DOVE), which will make dedicated measurements of the Venus thermosphere-ionosphere system and atmospheric escape, to address key gaps in our current understanding. DOVE will provide critical constraints on overlooked water loss and isotope fractionation processes, amplifying the science return of planned bulk atmosphere measurements and furthering a renewed global effort to understand the history of our sister planet

Measurement needs for understanding Venus water evolution

International audienceThe current dry state of Venus indicates that most of its water has been lost to space by a combination of early hydrodynamic and ongoing neutral and ion loss processes. The abundance and HDO/H2O ratio of the remaining water is regulated by hydrogen and deuterium escape to space, but there remains substantial uncertainty in the rate of present-day H loss, the relative importance of neutral H vs. H+ ion escape, and the fractionation factor of this escape. The interpretation of planned lower atmosphere measurements depends critically on these unconstrained upper atmosphere processes. For O and other heavier species, ion loss has likely played a major role, but existing measurements of ion escape are hopelessly separated from measurements of the ion source region by a poorly constrained transport and acceleration region, so that the processes controlling ion loss remain obscure. Further, ion supply, energization and transport, and finally escape are heavily influenced by the incoming flux of extreme ultraviolet photons and related changes in Venus’ external space environment. The substantial variations of these inputs over both solar cycle and geologic timescales, and their effects on key atmospheric processes, have not been sufficiently constrained. These unknowns frustrate the interpretation of lower and middle atmosphere observations, including those planned by future NASA and ESA missions, and inhibit the formulation of a self-consistent history for our sister planet. Here we call for new measurements of the Venus upper atmosphere and ionosphere to resolve these uncertainties and extend the scope of currently funded efforts to cover the entire atmosphere, from surface to space. The required remote sensing and in situ instruments are high-heritage, low mass, and low power, and the required altitude sampling and spatial coverage could be provided by a small spacecraft, yielding a transformative science return at relatively modest cost. A flotilla of space missions brought forth by an international community of scientists will soon visit Venus: upper atmosphere measurements, and the critical contributions they enable, must not be left behind