UCLA

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.

Deep-sea chemosynthetic communities may be particularly vulnerable to large climatic changes that affect ocean temperatures and circulation patterns. Chemosynthetic animals occupy narrow redox zones, mostly at hydrothermal vents, hydrocarbon seeps, or sites of organic deposition where subsurface fluids laden with reduced gases (e.g., sulfides, methane, hydrogen) meet oxygenated seawater. Dependence on chemolithoautotrophic bacteria as primary producers renders these communities susceptible to climatic changes that alter the breadth of the oxic/anoxic interface. The fossil record reveals major transitions of chemosynthetic faunas during the middle to late Mesozoic, failing to support prior hypotheses that these environments harbor an extraordinary number of ancient relics and living fossils. The molecular phylogenetic analyses summarized herein support Cenozoic (<65 Myr old) radiations for most of the dominant invertebrate taxa now occupying these habitats. Although stem ancestors for many of the mollusks, annelids and crustaceans found at vents and seeps survived the Cretaceous/Tertiary (K/T) extinction event, their contemporary crown taxa radiated mostly after the Paleocene/Eocene thermal maximum (PETM), which led to a widespread anoxic/dysoxic event in the world’s deep-ocean basins. Perhaps these findings provide a window for viewing the future of our oceans on a warming planet.

Polar ice sheets are progressively becoming one of the most critical components of the Earth System. Indeed, in a warming climate, the Antarctic and Greenland ice sheets are contributing larger amounts of fresh water to the oceans, which results in increasing sea level rise. Here, we look at recent developments within the Ice Sheet System Model (ISSM) that have resulted in improved projections of sea level rise. Our focus will be on understanding what uncertainties remain in such projections, and how to improve them using a combination of modeling and observations.

There is moderately strong evidence that the Earth experienced one or more magma ocean episodes during which large-scale magmas were at or close to the surface. Because the rates of heat loss is very high, such episodes could only be powered by impacts and the periods during which magma was exposed were very brief. It has been popular to discuss magma oceans in the Asteroid Belt; in particular, several studies have inferred that the HED (howardite, eucrite, diogenite) meteorites formed in a magma ocean on Vesta. In fact, it appears to be impossible to create true magma oceans in the Asteroid Belt because impact heating liberates less heat and 26Al heats at much too low a rate. What the authors really are discussing is global magmas located beneath an insulating megaregolithic shell. All igneous models of asteroids use 26Al as the heat source even though the 26Al/27Al ratios in the chondrites in our museums are too low to produce appreciable melting. The general justification is that impact heating doesn’t work so it must have been 26Al heating. In effect, 26Al is treated as a free parameter. Until recently this was justified because Hf/W model ages for iron meteorites implied that the irons are older than chondrites. And modelers are now producing large melt fractions in porous asteroids at relatively low impact velocities (~5 km s-1). The most cited paper justifying a magma ocean on the HED parent asteroid is by Greenwood et al. (2005) who showed that most HEDs formed a very tight cluster. The cluster does indeed imply a single, well mixed magma but the data only require a relatively small magma. In fact, the D17O and e54Cr data favor a model in which the HEDs form on the same asteroid as the IIIAB magmatic irons (and thus not on Vesta). Richter and Drake (1997) suggested that a magma ocean was the best way to explain the low alkali contents in eucrites. However, internal heating by 26Al is not expected to result in much volatile loss because there is no carrier phase at volatilization temperatures . Impact heat is probably much more efficient at evaporating alkalis. The isotopic links between the HEDs and IIIAB irons seem stronger than the spectroscopic links between HEDs and the surface of Vesta. These groups probably formed in one or more regional magmas produced by minor impacts on a porous asteroid.

In hopes of seeding ideas for joint UCLA-JPL projects, I will briefly
describe a half-dozen topics showing the capabilities at JPL for
modeling planet-forming environments in protostellar disks. The
common thread is our desire to translate the flood of data from
Spitzer, Herschel, SOFIA, ALMA, JWST and other telescopes into an
understanding of the origins of the observed population of planetary
systems. Specifically I’ll give a taste of our work on (1) young
planets perturbing their surroundings in ways that might soon be
observed, (2) delivering ices to planets massive enough to open a gap
in the circumstellar disk, (3) using molecular line emission to probe
turbulence in the disk atmosphere, (4) infrared variability as a gauge
of the disk magnetic activity, (5) the origins of Jupiter’s moons in a
circumplanetary disk, and/or (6) water abundances near the protosolar
disk’s snow line, in the face of destruction by stellar ultraviolet
photons.