Does Titan Have a 250 km Deep Ocean Beneath its Surface?

New insights on Titan's interior from its obliquity

Authors:

Noyelles et al

Abstract:

We constructed a 6-degrees of freedom rotational model of Titan as a 3-layer body consisting of a rigid core, a fluid global ocean, and a floating ice shell. The ice shell exhibits partially-compensated lateral thickness variations in order to simultaneously match the observed degree-two gravity and shape coefficients. The rotational dynamics are affected by the gravitational torque of Saturn, the gravitational coupling between the inner core and the shell, and the pressure coupling at the fluid-solid boundaries. Between 10 and 13% of our model Titans have an obliquity (due to a resonance with the 29.5-year periodic annual forcing) that is consistent with the observed value.

The shells of the successful models have a mean thickness of 130 to 140 km, and an ocean of ~250 km thickness. Our simulations of the obliquity evolution show that the Cassini obliquity measurement is an instantaneous one, and does not represent a mean value. Future measurements of the time derivative of the obliquity would help to refine the interior models. We expect in particular a variation of roughly 7 arcmin over the duration of the Cassini mission.

Modeling Titan's Internal Structure

Librational response of a deformed 3-layer Titan perturbed by non-keplerian orbit and atmospheric couplings

Authors:

Richard et al

Abstract:

The analyses of Titan's gravity field obtained by Cassini space mission suggest the presence of an internal ocean beneath its icy surface. The characterization of the geophysical parameters of the icy shell and the ocean is important to constrain the evolution models of Titan. The knowledge of the librations, that are periodic oscillations around a uniform rotational motion, can bring piece of information on the interior parameters. The objective of this paper is to study the librational response in longitude from an analytical approach for Titan composed of a deep atmosphere, an elastic icy shell, an internal ocean, and an elastic rocky core perturbed by the gravitational interactions with Saturn. We start from the librational equations developed for a rigid satellite in synchronous spin-orbit resonance. We introduce explicitly the atmospheric torque acting on the surface computed from the Titan IPSL GCM (Institut Pierre Simon Laplace General Circulation Model) and the periodic deformations of elastic solid layers due to the tides. We investigate the librational response for various interior models in order to compare and to identify the influence of the geophysical parameters and the impact of the elasticity. The main librations arise at two well-separated forcing frequency ranges: low forcing frequencies dominated by the Saturnian annual and semi-annual frequencies, and a high forcing frequency regime dominated by Titan's orbital frequency around Saturn. We find that internal structure models including an internal ocean with elastic solid layers lead to the same order of libration amplitude than the oceanless models, which makes more challenging to differentiate them by the interpretation of librational motion.

Nice Model for Kuiper Belt Objects has Some Problems

The Absolute Magnitude Distribution of Kuiper Belt Objects

Authors:

Fraser et al

Abstract:

Here we measure the absolute magnitude distributions (H-distribution) of the dynamically excited and quiescent (hot and cold) Kuiper Belt objects (KBOs), and test if they share the same H-distribution as the Jupiter Trojans. From a compilation of all useable ecliptic surveys, we find that the KBO H-distributions are well described by broken power-laws. The cold population has a bright-end slope, α1=1.5+0.4−0.2, and break magnitude, HB=6.9+0.1−0.2 (r'-band). The hot population has a shallower bright-end slope of, α1=0.87+0.07−0.2, and break magnitude HB=7.7+1.0−0.5. Both populations share similar faint end slopes of α2∼0.2. We estimate the masses of the hot and cold populations are ∼0.01 and ∼3×10−4 M⨁. The broken power-law fit to the Trojan H-distribution has α1=1.0±0.2, α2=0.36±0.01, and HB=8.3. The KS test reveals that the probability that the Trojans and cold KBOs share the same parent H-distribution is less than 1 in 1000. When the bimodal albedo distribution of the hot objects is accounted for, there is no evidence that the H-distributions of the Trojans and hot KBOs differ. Our findings are in agreement with the predictions of the Nice model in terms of both mass and H-distribution of the hot and Trojan populations. Wide field survey data suggest that the brightest few hot objects, with Hr'≲3, do not fall on the steep power-law slope of fainter hot objects. Under the standard hierarchical model of planetesimal formation, it is difficult to account for the similar break diameters of the hot and cold populations given the low mass of the cold belt.

Modeling the Differences Between Continental Collisions in the Phanerozoic and the PreCambrian

Contrasting styles of Phanerozoic and Precambrian continental collision

Authors:

Sizova et al

Abstract:

There are differences in the style of collisional orogens between the Phanerozoic and the Precambrian, most notably the appearance of blueschists and ultrahigh pressure metamorphic (UHPM) rocks in the geological record since the late Neoproterozoic, whereas these rocks are absent from older orogens. Understanding collisional orogenesis in the context of present-day values for ambient upper-mantle temperature and radiogenic heat production provides a reference from which to extrapolate back to conditions in the Precambrian. To evaluate differences in the way Phanerozoic and Precambrian collisional orogens develop, a series of experiments was run using a 2-D petrological–thermomechanical numerical model in which the collision of spontaneously moving continental plates was simulated for values of ambient upper-mantle temperature and radiogenic heat production increasing from those appropriate to the present-day. Thus, models of modern collisional orogens involving different modes of exhumation of UHPM rocks were extrapolated back to conditions appropriate for the Precambrian. Based on these experiments an increase of the ambient upper-mantle temperature to > 80–100 K above the present-day value leads to two distinct modes of collision that are different from the modern collision regime and for which the terms truncated hot collision regime (strong mafic lower continental crust) and two-sided hot collision regime (weak felsic lower continental crust) are proposed. Some Proterozoic orogens record post-extension thickening to generate counter-clockwise metamorphic P–T paths followed by slow close-to-isobaric retrograde cooling, such as occurred in the Paleoproterozoic Khondalite belt in the North China craton and the late Mesoproterozoic–early Neoproterozoic Eastern Ghats province, part of the Eastern Ghats belt of peninsular India. These orogens have similarities with the truncated hot collision regime in the numerical models, assuming subsequent shortening and thickening of the resulting hot lithosphere. Other Proterozoic orogens are characterized by clockwise looping metamorphic P–T paths and extensive granite magmatism derived from diverse crustal and subcontinental lithospheric mantle sources. These orogens have similarities with the two-sided hot collision regime in the numerical models. Both regimes are associated with shallow slab breakoff that precludes the formation of UHPM rocks. The temperature of the ambient upper-mantle where this transition in geodynamic regimes occurs corresponds broadly to the Neoproterozoic Era.

Using Leaf Fossil Types as Evidence of Habitat Openness

Using fossil leaves as evidence for open vegetation

Authors:

Jordan et al

Abstract:

The ability to discriminate between open vegetation and closed forest in the fossil record is constrained by a paucity of suitable proxies. Taxonomy-based proxies (especially the floristic composition of fossil pollen assemblages) provide the main tool for inferring vegetation type but this approach can be confounded by evolutionary changes in ecology, especially for ancient fossil assemblages. This paper considers a range of indicators of open vegetation that can be observed on fossil leaves. We show that the presence of amphistomatic leaves (i.e. leaves with stomata on both upper and lower surfaces) is unambiguously associated with open vegetation in the ecologically diverse family Proteaceae. This linkage shows very high levels of evolutionary convergence and the relationship is not explained by climate. Similar relationships are also present in a wide range of other plant groups. The combination of these empirical correlations and physiological theory suggests that there is a strong functional link between amphistomatic leaves and open vegetation. Theory says that amphistomy increases the efficiency of water transport and gas exchange by allowing two layers of high performance photosynthetic tissue to be proximal to sources of both carbon dioxide (stomata) and water (veins). However these benefits come at the cost of requiring thick leaves, which are inefficient in shaded environments. Other leaf characteristics observable on fossils (especially very thick cuticles, the presence of thick lignified hypodermal layers and the presence of deeply encrypted stomata) may also indicate the presence of open vegetation, although the functional links between these traits and vegetation type are more indirect. We propose that amphistomatic fossil leaves of dicotyledonous angiosperms provide a strong proxy for open vegetation but any inference will be enhanced by evidence from alternative proxies. We also provide an example of the application of this proxy.

Habitable Zone Model Predicts Larger Zone Than Previously Thought

Increased insolation threshold for runaway greenhouse processes on Earth-like planets

Authors:

Leconte et al

Abstract:

The increase in solar luminosity over geological timescales should warm the Earth’s climate, increasing water evaporation, which will in turn enhance the atmospheric greenhouse effect. Above a certain critical insolation, this destabilizing greenhouse feedback can ‘run away’ until the oceans have completely evaporated. Through increases in stratospheric humidity, warming may also cause evaporative loss of the oceans to space before the runaway greenhouse state occurs. The critical insolation thresholds for these processes, however, remain uncertain because they have so far been evaluated using one-dimensional models that cannot account for the dynamical and cloud feedback effects that are key stabilizing features of the Earth’s climate. Here we use a three-dimensional global climate model to show that the insolation threshold for the runaway greenhouse state to occur is about 375 W m−2, which is significantly higher than previously thought. Our model is specifically developed to quantify the climate response of Earth-like planets to increased insolation in hot and extremely moist atmospheres. In contrast with previous studies, we find that clouds have a destabilizing feedback effect on the long-term warming. However, subsident, unsaturated regions created by the Hadley circulation have a stabilizing effect that is strong enough to shift the runaway greenhouse limit to higher values of insolation than are inferred from one-dimensional models. Furthermore, because of wavelength-dependent radiative effects, the stratosphere remains sufficiently cold and dry to hamper the escape of atmospheric water, even at large fluxes. This has strong implications for the possibility of liquid water existing on Venus early in its history, and extends the size of the habitable zone around other stars.

New Stage of Planet Formation Described

AFTER RUNAWAY: THE TRANS-HILL STAGE OF PLANETESIMAL GROWTH

Author:

Yoram Lithwick

Abstract:

When planetesimals begin to grow by coagulation, they first enter an epoch of runaway, during which the biggest bodies grow faster than all the others. The questions of how runaway ends and what comes next have not been answered satisfactorily. We show that runaway is followed by a new stage—the "trans-Hill stage"—that commences when the bodies that dominate viscous stirring ("big bodies") become trans-Hill, i.e., when their Hill velocity matches the random speed of the small bodies they accrete. Subsequently, the small bodies' random speed grows in lockstep with the big bodies' sizes, such that the system remains in the trans-Hill state. Trans-Hill growth is crucial for determining the efficiency of growing big bodies, as well as their growth timescale and size spectrum. Trans-Hill growth has two sub-stages. In the earlier one, which occurs while the stirring bodies remain sufficiently small, the evolution is collisionless, i.e., collisional cooling among all bodies is irrelevant. The efficiency of forming big bodies in this collisionless sub-stage is very low, ~10α Lt 1, where α ~ 0.005(a/AU)–1 is the ratio between the physical size of a body and its Hill radius. Furthermore, the size spectrum is flat (equal mass per size decade, i.e., q = 4). This collisionless trans-Hill solution explains results from previous coagulation simulations for both the Kuiper Belt and the asteroid belt. The second trans-Hill sub-stage commences once the stirring bodies grow big enough (greater than α–1 × the size of the accreted small bodies). After that time, collisional cooling among small bodies controls the evolution. The efficiency of forming big bodies rises and the size spectrum becomes more top heavy. Trans-Hill growth can terminate in one of two ways, depending on the sizes of the small bodies. First, mutual accretion of big bodies can become significant and conglomeration proceeds until half of the total mass is converted into big bodies. This mode of growth may explain the observed size distributions of small bodies in the solar system and is explored in our subsequent work. Second, if the big bodies' orbits become separated by their Hill radius, oligarchy commences. This mode likely precedes the formation of fully fledged planets.

Modeling Europa's Ocean Circulation

In a finding of relevance to the search for life in our solar system, researchers at The University of Texas at Austin's Institute for Geophysics, the Georgia Institute of Technology, and the Max Planck Institute for Solar System Research have shown that the subsurface ocean on Jupiter's moon Europa may have deep currents and circulation patterns with heat and energy transfers capable of sustaining biological life.

Scientists believe Europa is one of the planetary bodies in our solar system most likely to have conditions that could sustain life, an idea reinforced by magnetometer readings from the Galileo spacecraft detecting signs of a salty, global ocean below the moon's icy shell.

Without direct measurements of the ocean, scientists have to rely on magnetometer data and observations of the moon's icy surface to account for oceanic conditions below the ice.

Regions of disrupted ice on the surface, known as chaos terrains, are one of Europa's most prominent features. As lead author Krista Soderlund and colleagues explain in this week's online edition of the journal Nature Geosciences, the chaos terrains, which are concentrated in Europa's equatorial region, could result from convection in Europa's ice shell, accelerated by heat from the ocean. The heat transfer and possible marine ice formation may be helping form diapirs, or warm compositionally buoyant plumes of ice that rise through the shell.

In a numerical model of Europa's ocean circulation, the researchers found that warm rising ocean currents near the equator and subsiding currents in latitudes closer to the poles could account for the location of chaos terrains and other features of Europa's surface. Such a pattern coupled with regionally more vigorous turbulence intensifies heat transfer near the equator, which could help initiate upwelling ice pulses that create features such as the chaos terrains.

"The processes we are modeling on Europa remind us of processes on Earth," says Soderlund, where a similar process has been observed in the patterns creating marine ice in parts of Antarctica.

The current patterns modeled for Europa contrast with the patterns observed on Jupiter and Saturn, where bands of storms form because of the way their atmospheres rotate. The physics of Europa's ocean appear to have more in common with the oceans of the "ice giants" Uranus and Neptune, which show signs of three-dimensional convection.

"This tells us foundational aspects of ocean physics," notes co-author Britney Schmidt, assistant professor at the Georgia Institute of Technology. More importantly, adds Schmidt, if the study's hypothesis is correct, it shows that Europa's oceans are very important as a controlling influence on the surface ice shell, offering proof of the concept that ice-ocean interactions are important to Europa.

"That means more evidence that the ocean is there, that it's active, and there are interesting interactions between the ocean and ice shell," says Schmidt, "all of which makes us think about the possibility of life on Europa."

link.

Pterosaurs Were NOT Birds, Especially Floating in Water

The posture of floating pterosaurs: Ecological implications for inhabiting marine and freshwater habitats

Authors:

David WE Hone and Donald M Henderson

Abstract:

The highly pneumatic skeleton of the extinct flying pterosaurs suggests that they would float high up on open water, but in a posture rather different to that of birds. However, the exact posture of the body and head remains unknown and would be critical for an ocean going pterosaur forced onto the waters’ surface or animals that alighted to feed. Using computational methods with recent models and body mass estimates for four pterosaur genera – Dimorphodon, Rhamphorhynchus, Pteranodon and Dsungaripterus we show that the floating posture of pterodactyloid pterosaurs led to the head, neck and body being horizontal with the ventral 1/4 to 1/3 being immersed, and the external nares being almost at, or potentially partially below, the waterline that could have left them vulnerable to drowning. The floatation methods were verified using a model of a Canada goose (Branta canadensis) that is able to successfully replicate the expected orientation and depth of immersion of the bird. While there is convincing evidence for a number of pterosaurs foraging in marine and freshwater environments, these results suggest many did not regularly rest on the surface of the water and if immersed would need to take off again rapidly. The high numbers of fossils of juvenile pterosaurs compared to the terrestrial Mesozoic dinosaurs suggests that this may be linked to their poor ability in water.

Are We Underestimating Climate Change?

Many scientists believe that global warming will come to an end if, some day, human succeeds in stopping the release of greenhouse gas emissions into the atmosphere. It would, indeed, be hotter on Earth than before industrialisation, but nonetheless it would not get even hotter. Climate physicist Thomas Frölicher questions this notion by using model calculations and creates a more pessimistic picture in a study published in the scientific journal Nature Climate Change. According to his model calculations, it is very possible that the Earth's atmosphere could continue to warm for hundreds of years even after a complete stop of CO2 emissions, and that temperature levels stabilise at an even higher level at a later stage. "In the long term, the temperature increase could be 25 per cent greater than assumed today," says the scientist, who carries out research as an Ambizione Fellow of the Swiss National Science Foundation in ETH professor Nicolas Gruber's group.

link.

More Details of the Environmental Degradation of the Permian Triassic Extinction

Acid rain and ozone depletion from pulsed Siberian Traps magmatism

Authors:

Black et al.

Abstract:

The Siberian Traps flood basalts have been invoked as a trigger for the catastrophic end-Permian mass extinction. Widespread aberrant plant remains across the Permian-Triassic boundary provide evidence that atmospheric stress contributed to the collapse in terrestrial diversity. We used detailed estimates of magmatic degassing from the Siberian Traps to complete the first three-dimensional global climate modeling of atmospheric chemistry during eruption of a large igneous province. Our results show that both strongly acidic rain and global ozone collapse are possible transient consequences of episodic pyroclastic volcanism and heating of volatile-rich Siberian country rocks. We suggest that in conjunction with abrupt warming from greenhouse gas emissions, these repeated, rapidly applied atmospheric stresses directly linked Siberian magmatism to end-Permian ecological failure on land. Our comprehensive modeling supplies the first picture of the global distribution and severity of acid rain and ozone depletion, providing testable predictions for the geography of end-Permian environmental proxies.

Studying the Atmospheric Eddies of Titan

A non-monotonic eddy diffusivity profile of Titan's atmosphere revealed by cassini observations

Authors:

Li et al


Abstract:

Recent measurements from the limb-view soundings of Cassini/CIRS and the stellar occultations from Cassini/UVIS revealed the complete vertical profiles of minor species (e.g., C2H2 and C2H4) from 100 to 1000km in the atmosphere of Titan. In this study, we developed an inversion technique to retrieve the eddy diffusion profile using C2H2 as a tracer species. The retrieved eddy profile features a low eddy diffusion zone near the altitude of the detached haze layer (∼550km), which could be a consequence of stabilization through aerosol heating. Photochemical modeling results using the retrieved eddy profile are in better agreement with the Cassini measurements than previous models. The underestimation of C2H4 in the stratosphere has been a long-standing problem in planetary photochemical modeling, and the new eddy diffusion profile does not solve this problem. In order to match the observations, we suggest a new expression for the rate coefficient of the key reaction, H+C2H4+M⟶C2H5+M. The new reaction rate coefficient is estimated to be ∼10 times lower than that used by Moses et al. (2005)'s model, and should be validated in the laboratory and tested against the hydrocarbon chemistry of giant planets.

Will Supercomputers Massively Change Material Science?

Engineered materials such as chip-grade silicon and fiber-optic glass underpin the modern world. Yet designing new materials has historically involved a frustrating and inefficient amount of guesswork.

Streamlined versions of the equations of quantum mechanics—along with supercomputers that, using those equations, virtually test thousands of materials at a time—are eliminating much of that guesswork.

Researchers are now using this method, called high-throughput computational materials design, to develop new batteries, solar cells, fuel cells, computer chips, and other technologies.

link.

Edging Towards the Inner Distance of the Habitable Zone

TOWARD THE MINIMUM INNER EDGE DISTANCE OF THE HABITABLE ZONE

Authors:

Andras Zsom, Sara Seager, Julien de Wit, and Vlada Stamenković

Abstract:

We explore the minimum distance from a host star where an exoplanet could potentially be habitable in order not to discard close-in rocky exoplanets for follow-up observations. We find that the inner edge of the Habitable Zone for hot desert worlds can be as close as 0.38 AU around a solar-like star, if the greenhouse effect is reduced (~1% relative humidity) and the surface albedo is increased. We consider a wide range of atmospheric and planetary parameters such as the mixing ratios of greenhouse gases (water vapor and CO2), surface albedo, pressure, and gravity. Intermediate surface pressure (~1-10 bars) is necessary to limit water loss and to simultaneously sustain an active water cycle. We additionally find that the water loss timescale is influenced by the atmospheric CO2 level, because it indirectly influences the stratospheric water mixing ratio. If the CO2 mixing ratio of dry planets at the inner edge is smaller than 10–4, the water loss timescale is ~1 billion years, which is considered here too short for life to evolve. We also show that the expected transmission spectra of hot desert worlds are similar to an Earth-like planet. Therefore, an instrument designed to identify biosignature gases in an Earth-like atmosphere can also identify similarly abundant gases in the atmospheres of dry planets. Our inner edge limit is closer to the host star than previous estimates. As a consequence, the occurrence rate of potentially habitable planets is larger than previously thought.

Livermore Study Ties Precipitation and Global Warming Changes

The rain in Spain may lie mainly on the plain, but the location and intensity of that rain is changing not only in Spain but around the globe.

A new study by Lawrence Livermore National Laboratory scientists shows that observed changes in global (ocean and land) precipitation are directly affected by human activities and cannot be explained by natural variability alone. The research appears in the Nov. 11 online edition of the Proceedings of the National Academy of Sciences.

Emissions of heat-trapping and ozone-depleting gases affect the distribution of precipitation through two mechanisms. Increasing temperatures are expected to make wet regions wetter and dry regions drier (thermodynamic changes); and changes in atmospheric circulation patterns will push storm tracks and subtropical dry zones toward the poles.

"Both these changes are occurring simultaneously in global precipitation and this behavior cannot be explained by natural variability alone," said LLNL's lead author Kate Marvel. "External influences such as the increase in greenhouse gases are responsible for the changes."

The team compared climate model predications with the Global Precipitation Climatology Project's global observations, which span from 1979-2012, and found that natural variability (such as El Niños and La Niñas) does not account for the changes in global precipitation patterns. While natural fluctuations in climate can lead to either intensification or poleward shifts in precipitation, it is very rare for the two effects to occur together naturally.

"In combination, manmade increases in greenhouse gases and stratospheric ozone depletion are expected to lead to both an intensification and redistribution of global precipitation," said Céline Bonfils, the other LLNL author. "The fact that we see both of these effects simultaneously in the observations is strong evidence that humans are affecting global precipitation."

Marvel and Bonfils identified a fingerprint pattern that characterizes the simultaneous response of precipitation location and intensity to external forcing.

link.

Modeling the Locomotion of Sauropod Argentinosaurus huinculensis (with video)

March of the Titans: The Locomotor Capabilities of Sauropod Dinosaurs

Authors:

William Irvin Sellers, Lee Margetts, Rodolfo Anı´bal Coria and Phillip Lars Manning

Abstract:

Sauropod dinosaurs are the largest terrestrial vertebrate to have lived on Earth. This size must have posed special challenges for the musculoskeletal system. Scaling theory shows that body mass and hence the loads that must be overcome increases with body size more rapidly than either the ability of the muscles to generate force, or the ability of the skeleton to support these loads. Here we demonstrate how one of the very largest sauropods, Argentinosaurus huinculensis (40 metres long, weighing 83 tonnes), may have moved. A musculoskeletal model was generated using data captured by laser scanning a mounted skeleton and assigning muscle properties based on comparative data from living animals. Locomotion is generated using forward dynamic simulation to calculate the accelerations produced by the muscle forces, coupled with machine learning technique to find a control pattern that minimises metabolic cost. The simulation demonstrates that at such vast body size, joint range of motion needs to be restricted to allow sufficient force generation for an achievable muscle mass. However when this is done, a perfectly plausible gait can be generated relatively easily. Whilst this model represents the best current simulation of the gait of these giant animals, it is likely that there are as yet unknown mechanical mechanisms, possibly based on passive elastic structures that should be incorporated to increase the efficiency of the animal9s locomotion. It is certainly the case that these would need to be incorporated into the model to properly assess the full locomotor capabilities of the animal.

Increased Understanding of the Orbits of Multi Exoplanet Systems

DISK-PLANETS INTERACTIONS AND THE DIVERSITY OF PERIOD RATIOS IN KEPLER'S MULTI-PLANETARY SYSTEMS

Authors:

Clement Baruteau and John C. B. Papaloizou

Abstract:

The Kepler mission is dramatically increasing the number of planets known in multi-planetary systems. Many adjacent planets have orbital period ratios near resonant values, with a tendency to be larger than required for exact first-order mean-motion resonances. This feature has been shown to be a natural outcome of orbital circularization of resonant planetary pairs due to star-planet tidal interactions. However, this feature holds in multi-planetary systems with periods longer than 10 days, in which tidal circularization is unlikely to provide efficient divergent evolution of the planets' orbits to explain these orbital period ratios. Gravitational interactions between planets and their parent protoplanetary disk may instead provide efficient divergent evolution. For a planet pair embedded in a disk, we show that interactions between a planet and the wake of its companion can reverse convergent migration and significantly increase the period ratio from a near-resonant value. Divergent evolution due to wake-planet interactions is particularly efficient when at least one of the planets opens a partial gap around its orbit. This mechanism could help account for the diversity of period ratios in Kepler's multiple systems from super-Earth to sub-Jovian planets with periods greater than about 10 days. Diversity is also expected for pairs of planets massive enough to merge their gap. The efficiency of wake-planet interactions is then much reduced, but convergent migration may stall with a variety of period ratios depending on the density structure in the common gap. This is illustrated for the Kepler-46 system, for which we reproduce the period ratio of Kepler-46b and c.

Simulation of the Carbon Release During the Permian Extinction and its Consequences

Initial assessment of the carbon emission rate and climatic consequences during the end-Permian mass extinction

Authors:

Ying Cui, Lee R. Kump and Andy Ridgwell

Abstract:

Numerous lines of geochemical and stable isotopic evidence indicate that the end-Permian mass extinction was accompanied by abrupt climate change induced by CO2 addition. Catastrophic end-Permian Siberian volcanism may have released a large amount of CO2 into the atmosphere and pushed the Earth's system beyond a critical threshold, causing the mass extinction. However, the injection rate, total amount and source of CO2 are largely unknown. We conducted a suite of simulations using the recently published carbon isotope records and U–Pb ages from Meishan section in Zhejiang province, China. An Earth System Model of Intermediate Complexity (cGENIE; http://www.genie.ac.uk) was used to extract the pattern of CO2 release needed to replicate the observed carbon isotope excursion across the Permian-Triassic boundary. This analysis leads us to suggest that the source of CO2 must have been significantly heavier than typical biogenic or thermogenic methane to explain the significant warming that occurred during and after the extinction event. Nevertheless, as with the Paleocene-Eocene Thermal Maximum, end-Permian rates of CO2 addition were likely small compared with modern fossil-fuel burning, but considerably more protracted, such that the likely total CO2 emitted significantly exceeded the modern fossil-fuel reserves. Peak emission rates corresponded to the onset of the maximum extinction interval, consistent with carbon cycle disruption, including volcanogenic CO2-induced warming (and perhaps ocean acidification), as a trigger for the end-Permian mass extinction.

Carbon Cycle Models Neglect the Very Nontrivial Effects of Animals

Animal populations can have a far more significant impact on carbon storage and exchange in regional ecosystems than is typically recognized by global carbon models, according to a new paper authored by researchers at the Yale School of Forestry & Environmental Studies (F&ES).

In fact, in some regions the magnitude of carbon uptake or release due to the effects of specific animal species or groups of animals — such as the pine beetles devouring forests in western North America — can rival the impact of fossil fuel emissions for the same region, according to the paper published in the journal Ecosystems.

While models typically take into account how plants and microbes affect the carbon cycle, they often underestimate how much animals can indirectly alter the absorption, release, or transport of carbon within an ecosystem, says Oswald Schmitz, the Oastler Professor of Population and Community Ecology at F&ES and lead author of the paper. Historically, the role of animals has been largely underplayed since animal species are not distributed globally and because the total biomass of animals is vastly lower than the plants that they rely upon, and therefore contribute little carbon in the way of respiration.

"What these sorts of analyses have not paid attention to is what we call the indirect multiplier effects," Schmitz says. "And these indirect effects can be quite huge – and disproportionate to the biomass of the species that are instigating the change."

In the paper, "Animating the Carbon Cycle," a team of 15 authors from 12 universities, research organizations and government agencies cites numerous cases where animals have triggered profound impacts on the carbon cycle at local and regional levels.

In one case, an unprecedented loss of trees triggered by the pine beetle outbreak in western North America has decreased the net carbon balance on a scale comparable to British Columbia's current fossil fuel emissions.

And in East Africa, scientists found that a decline in wildebeest populations in the Serengeti-Mara grassland-savanna system decades ago allowed organic matter to accumulate, which eventually led to about 80 percent of the ecosystem to burn annually, releasing carbon from the plants and the soil, before populations recovered in recent years.

"These are examples where the animals' largest effects are not direct ones," Schmitz says. "But because of their presence they mitigate or mediate ecosystem processes that then can have these ramifying effects."

link.

An Improved Simulation of Venusian Northern Hemisphere's Atmosphere

Self-consistent retrieval of temperature profiles and cloud structure in the northern hemisphere of Venus using VIRTIS/VEX and PMV/VENERA-15 radiation measurements

Authors:

Rainer Haus, David Kappel and Gabriele Arnold

Abstract:

Improved radiative transfer simulation and multi-window retrieval procedures (MWR) are described that are applied to investigate thermal structure and cloud features in the nightside atmosphere of Venus over the northern hemisphere. Comparative analyses of spectroscopic data, which were recorded independently in different parts of the infrared spectrum by the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS-M-IR) aboard ESA's Venus Express space probe and the Profile Measuring Instrument for Venus (PMV, Fourier spectrometer FS-1/4) during the earlier Soviet Venera-15 experiment, are combined with self-consistent temperature profile and cloud parameter retrievals. MWR performance is studied using synthetic spectra at different latitudes and for different atmospheric temperature profiles and cloud parameters. VIRTIS and PMV retrieval result comparisons are used to determine constraints on physical state parameter variations, especially on applicability of different cloud models. An analytically parameterized initial model of four-modal cloud altitude distributions is proposed. Together with retrieved cloud parameters, which encompass individual mode factors and cloud upper altitude boundary, it permits optimum fits of measured radiances and brightness temperatures in the 4.3 and 15 µm CO2 bands utilized for atmospheric temperature profile retrievals. A new multi-spectrum retrieval (MSR) method (Kappel et al., 2012, 2013) provides deep atmosphere CO2 opacity correction parameters, which affect cloud parameter retrievals from short-wavelength emission windows.

The main features of retrieved latitude and altitude-dependent temperature fields (zonal averages) are in good quantitative accordance with earlier obtained results. Prominent structures like ‘cold collar’ and ‘hot dipole’ are re-examined. The cold inversion layer is centered at about 62–66 km and 55 and 75°N. Below the collar, temperature usually decreases with latitude at the same altitude, while it typically increases toward the pole above 70 km. Absolute temperature differences between zonal averages of VIRTIS and PMV results are usually below 3 K between 58 and 80 km, while a 9 K lower VIRTIS temperature is only observed at 75°N near 60 km. Both VIRTIS and PMV retrievals reveal a slow decrease of cloud top altitude from about 71 km at the equator to about 70 km at mid latitudes. Northward of 55°N, it quickly descends down to about 61.5 km at polar latitudes in accordance with earlier results. Cloud particle size and total cloud optical depth exhibit a minimum at 50°N and increase towards the equator and the North Pole. The hemispheric average of cloud opacity derived from VIRTIS data is 34.7 at 1 µm.