Category: Seminars

Planetary oceanography is a developing field of study full of opportunities for discovering and understanding new phenomena that might be observed by future missions. I will describe laboratory measurements of sound velocities in simulated icy world ocean solutions at relevant pressures, temperatures, and compositions, leading to self-consistent thermodynamic data sets. Applications of results from this work constrain the configuration of oceans and ices in Ganymede, and provide new insight into the structure of Europa’s ocean and its interaction with the overlying ice.

On 20 April 2010, while drilling at the Macondo Prospect, situated at the Mississippi Canyon block 252 (MC252), an explosion on the Deepwater Horizon rig caused by a blowout killed 11 crewmen and ignited a fireball visible from 35 miles (56 km) away. Two days later, the rig sank, leaving the well gushing at the seabed and causing the largest offshore oil spill in U.S. history: some 5,000,000 bbl (210,000,000 gal) released into the Gulf of Mexico. The setting of the spill is quite different from other historic marine oil spills that occurred at or near the sea surface. The Deepwater hydrocarbons were released at a depth of ~1,500 m (water pressure ~160 atm) in a high pressure jet (~500 atm), resulting in gas bubbles and liquid oil droplets of different size. Size and chemical composition of the hydrocarbon bubbles and droplets evolved extremely rapidly following release from the well. A complex interplay of physical and biochemical processes determined hydrocarbon-water plume mixing dynamics and affected the composition and spatial distribution of the hydrocarbon mixtures within the water column, at the surface in the resulting oil slick, and in the overlying atmosphere. This presentation considers impact of multiple sources of oil contamination and evaluates the role of different oil weathering processes that change the chemical composition of oil in deep water and their effect on the long-term fate of oil in the Gulf of Mexico coastal waters.

At the current rate of global C emissions and without substantial mitigation efforts, atmospheric CO2 is projected to increase by the end of this century to levels not previously experienced on Earth since the onset of our current glacial state. Although Earth has been an icehouse for the past 34 million years, warmer greenhouse conditions have been the ‘typical’ climate state of the past half billion years. Unique insight into how the Earth system will function in such an evolving and high CO2 environment resides in the deep-time analogs of past climate and ecosystem response to greenhouse gas-forced warming of the magnitude comparable to that which we may ultimately face. The deep-time archive, a fully integrated record of climate-ecosystem interactions and feedbacks prompted by high levels of radiative forcing, reveals climate change in the past that was at times far more dynamic than suggested by reconstructions of the past few hundred thousand years. And records of past abrupt change reveal the much slower pace of naturally forced periods of global warming. The association of these periods with critical climate and ecological thresholds provides a context for the future. The inability of numeric climate models to reconstruct surface environmental conditions of past warm periods suggested by proxy records highlights the existence of fundamental processes in the climate system that require further evaluation, and which might indicate that climate projections for our future may well be underestimated. This presentation will discuss – in the context of projected atmospheric CO2 levels – examples of past major transitions that illustrate how greenhouse-gas forced climate change has unfolded in the past and that characterize the fingerprints of climate and ecological thresholds.

The first observation of a chemically produced mass independent process suggested application to the early solar system, which remains relevant to date. In the subsequent development of a quantum mechanical understanding of the isotopic process, numerous applications in the terrestrial atmosphere arose. At present, with the exception of water, every oxygen bearing species in the Earths atmosphere is mass independent and does not lie on the so called terrestrial fractionation line, with species both above and below the fractionation line defined by silicate rocks. In each case, new information on source strengths and transport and chemical transformation is provided that would otherwise have been unrecognized. One of the least understood components of global climate is the role of aerosol particles. The application of mass independent isotope measurements has lead to new insights into this issue. Specific aspects of the role of particles with ozone has been particularly important as the role of chemically transformation is captured. What is more important is that the record is stable and the change over time is recorded and ice core samples provide the only paleo ozone record available. Finally, measurements of Martian meteorites secondary minerals may be better interpreted from combined laboratory, atmospheric, and ice core and geologic record. Recent measurements will be discussed

Despite almost a century of modern solar observations and over 50 years of space exploration, some of the fundamental problems in solar physics are not fully understood yet. The solar corona heating, the solar wind acceleration, the initiation and propagation of Coronal Mass Ejections (CMEs), and the solar cycle do not have a complete theoretical framework to describe and predict these phenomena. The lack of a complete theory, in addition to the large range of both spatial and temporal scales involved, make it challenging to develop numerical models for solar and space physics. Despite of the challenges, a great progress has been made in the last decade to develop numerical models for the solar corona, the solar wind , and CMEs. In my talk, I will describe a state of the art model for the solar corona and the solar wind, and I will demonstrate how the model can be used to improve our understanding on solar corona phenomena and observations.

The magnetic field is fundamental to solar activity and shapes the interplanetary environment, as clearly shown by the full three dimensional monitoring of the heliosphere provided by the measurements of the Helios, Ulysses, SOHO, ACE, Wind, STEREO, SDO and Voyager spacecraft. Magnetic fields are also the source for coronal heating and the very existence of the solar wind; produced by the sun’s dynamo and emerging into the corona, magnetic fields become a conduit for waves, act to store energy and then propel plasma into the heliosphere in the form of Coronal Mass Ejections (CMEs). Transformation of magnetic energy is also the source solar energetic particle events. The way in which solar convective energy couples to magnetic fields to produce the multifaceted heliosphere is at the heart of Solar Probe Plus (SPP) exploration. In this talk I will review the role played by the magnetic field in solar and heliospheric variability and solar atmospheric dynamics, including the coronal heating and solar wind acceleration problems. I will then highlight the exciting perspectives for discovery provided by SPP and other future missions to the inner heliosphere. Tests of current theoretical models of coronal heating and wind acceleration will be described and focus areas for further numerical and theoretical efforts illustrated.

Many exoplanets are on close-in orbits and are likely tidally synchronized. Atmospheric circulation affects the temperature distribution and thus transit observations of these planets. In particular, hot spots shifted by broad, steady, superrotating jets have been emphasized in the literature, but vortices can also play an important role. The scale of jets and vortices is expected to be large for this type of planets, which makes their possible time variability crucial. Our goal is to explore dominant circulation patterns and constrain conditions and mechanisms for variability on tidally locked exoplanets.

We use a general circulation model, solving the primitive equations with thermal relaxation. The parameter space relevant for tidally synchronized planets is explored, using the mini-Neptune GJ1214b and hot Jupiter HD209458b as reference planets. Furthermore, results are compared from models using different numerical algorithms and grids for a range of relevant test cases.

For a large range of conditions, robust features include a small number of jets and large-scale vortices. The vortices often exhibit time variability, associated with planetary scale waves, with corresponding variability in the position of relative hot and cold regions.

The results make a strong case for mission concepts such as ESA’s EChO, that emphasize repeated measurements of a given planet. The feedback between such observations and modeling offers an opportunity to gain new insights into exoplanet atmospheres from the time modulation of the signals, in addition to spatial variability.

Data extracted from the Extrasolar Planets Encyclopaedia (http://exoplanet.eu) show the existence of planets that are more massive than same-size iron cores. After meticulous verification of the data, we have concluded that the mass of the smallest of these planets was actually unknown. However, three high-density planets, Kepler-52b, Kepler-52c, and Kepler-57b, which are between 30 and 100 times the Earth mass, have indeed density larger than asame-size iron planet. This observation triggered the present study that investigates under which conditions these planets could represent the naked cores of gas giants that would have lost their atmospheres during their migration towards the star. The bulk viscosity of the cores of giant planets can indeed be large enough to hold a very high density during geological timescales. This would make those planets a new kind of planets which, in return, would provide useful information on the interior structure of the gas giants.

The active cryovolcanism on Enceladus and the formation of heavy organic molecules in Titan’s atmosphere are two major unrelated discoveries of the Cassini mission. These two end-member icy moons of Saturn reveal important processes for our understanding of the evolution of icy moons and their habitability potential. New observations by the Visual and Infrared mapping spectrometer (VIMS) onboard the Cassini spacecraft provide additional constraints on the geological processes responsible for the formation of Enceladus’ jets. The very strong correlation between the brightness of the overall plume and the true anomaly suggests a very strong control by tidal forces as expected by previous models. On Titan, the solar occultation observations provide constraints on the composition of the organic haze by comparing their spectral properties with those of heavy organic molecules synthetized in laboratory experiments simulating Titan’s conditions. These observations also give density profiles from which one can derive the flux of organic particle falling on Titan’s surface. These observations are included in a global model describing the carbon cycle on Titan and the relationships between the different reservoirs including atmospheric methane, organic haze, lakes, seas, dune fields, subsurface clathrate hydrates and a potential deep reservoir.

Our understanding of Jupiter and Saturn goes hand in hand with the availability and accuracy of observational constraints as well as of the equations of state for their main constituents, hydrogen and helium. We show how the current uncertainties in the core mass of Jupiter (0-10 ME) and Saturn (0-20 ME) could be reduced with the help of measured atmospheric oxygen abundances, which is in reach for Jupiter thanks to the Juno mission, and possibly also for Saturn. Given that both planets’ atmospheres are observed to be depleted in helium, we finally discuss the occurrence of H/He demixing with respect to recent ab initio data based H/He phase diagrams and argue that the assumption a layered structure with few layers remains a reasonable approximation. However, we caution that the derived total heavy element fraction is highly subject to our assumption of an adiabatic interior, which may not hold in case of He demixing.