Planetary Science Seminar - spring-2018

April 5, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Reny Hu - JPL

The number of planets we know increased by two orders of magnitude in the past decade. Many of the planets discovered beyond our solar system, i.e., exoplanets, have surprising traits, including having orbital periods of a mere few days, being larger than Earth and smaller than Neptune, and having atmospheric compositions where data suggest deviation from chemical equilibrium. These discoveries necessarily reorient our study of planetary atmospheres. I will discuss how observations of exoplanet atmospheres help us better understand the physical and chemical processes that control planetary atmospheres as well as the evolution of planets. For example, strong stellar irradiation and intermediate size of some exoplanets enable the formation of helium atmospheres, resulting in distinctive remote sensing spectral features. Observations of Hubble and JWST thus provide the opportunity to study the atmospheric evolution of super-Earths and sub-Neptunes. Looking ahead, I will conclude by describing pathways forward to characterize cold planets at wide orbital separations and search for potential signs of habitability from these distant worlds.

April 12, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Erin Leonard - UCLA

The young (<100 Ma) surface of Jupiter’s icy satellite Europa raises the key questions: What are the resurfacing mechanisms causing Europa to have a young surface, and how have these processes evolved through time? To address these questions we map and analyze (1) the USGS global image mosaic of Europa and (2) nine high-resolution frames obtained by the Galileo Solid State Imager (SSI) during the E12 flyby of Europa in Dec. 1997. From this analysis we find that local-scale resurfacing mechanisms have transitioned from distributed to discrete deformation, expressed by the transition in the formation of the ridged plains to the formation of chaos and isolated fractures. This finding is consistent with simultaneous ice-shell thickening and cooling occurring as the ice-shell deformed. In this talk, I will discuss the analysis and mapping of the global and high-resolution images and propose a synthesized hypothesis for the cyclic deformation that shapes Europa’s icy surface.

April 19, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Nigel Kelly - University of Colorado

Ongoing developments in our understanding of the behavior of low-temperature chronometers, coupled with our ability to model this behavior, has presented new opportunities to characterize the thermal histories of samples from the Moon, Mars and elsewhere in the Solar System. Using an example from lunar impact melt breccia 14311, I will demonstrate the utility of zircon (U-Th)/He thermochronometry in sampling lower energy impact events on the moon and other planetary bodies, and how thermal history modeling may provide constraints on the temperatures experienced by samples during impact events. When integrated with higher temperature chronometers such as U-Pb in zircon, these techniques allow a longer and more complete impact history to be teased from these complex rock samples. The talk will cover the basics of the technique, future possibilities, and limitations on application to non-terrestrial samples.

April 26, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Sean Falk - UCLA
• Kynan Hughson - UCLA

Sean Faulk: Surface-atmosphere connections on Titan Titan harbors a rich hydroclimate with geomorphological evidence of surface runoff, subsurface reservoirs, and sediment transport by intense rainstorms. Regional patterns in these surface features suggest corresponding regional climatic influences, namely in the form of precipitation from the atmosphere. A model coupling the atmosphere to a surface hydrology scheme is therefore required to fully explore Titan’s surface-atmosphere connections. Previous general circulation models (GCMs) of Titan have successfully reproduced Titan’s climate but have neglected basic representations of surface hydrology. I will present a new Titan GCM that includes simple parameterizations of surface and subsurface flow, infiltration, and groundwater evaporation, and discuss the resulting large-scale climate dynamics. The model promotes poleward methane transport by surface/subsurface flows into saturated high-latitude lowlands and equatorward methane transport by the atmosphere into unsaturated low-latitude highlands. Infiltration into unsaturated soils then dries the lower latitudes. The model therefore reproduces Titan’s observed equatorial desert and polar wetlands regions but within a more physically consistent framework than past GCMs. Kynan Hughson: Will it bend? Probing the mechanical properties of the shallow subsurface of Ceres from fractured terrains in its Nar Sulcus region. Nar Sulcus is a unique geomorphic terrain located in the southwest quadrant of Yalode crater on Ceres’ southern hemisphere. Geological mapping of the fractured terrain revealed that it contains two sets of mutually perpendicular fractures that we interpret to be low angle normal faults. We test the hypothesis that the topography and morphology of the Nar Sulcus normal faults are controlled primarily by a thin ice-rich elastic layer. We do this by mapping the structures in Nar Sulcus from Dawn spacecraft images, comparing their profiles to a single layer flexural-cantilever model for normal faulting similar to the one developed by Kusznir et al. (1991), and analyzing their displacement:length ratios using a method similar to the technique described in Cowie and Scholz (1992). This analysis, which is similar to the one conducted on the europan ice shell by Nimmo and Schenk (2006), estimates the elastic thickness and remote stress acting on the faults at Nar Sulcus.

May 3, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Jonathan Fortney - Univ. California Santa Cruz

The field of exoplanet atmospheres has advanced steadily over the past ~15 years due to the interplay of observations and modeling. Although typically hampered by telescope instrumentation that was never designed to study exoplanet spectra, the broad outlines of the atmospheres of Jupiter-class, Neptune-class, and sub-Neptune-class planets are starting to come into focus. I will touch on some recent highlights in the modeling of hot Jupiters as a class and the well-studied prototype warm Neptune GJ 436b. I&#39;ll close with a look towards JWST, and also theoretical expectations for rocky planets in late 2030&#39;s by potential NASA telescopes like LUVOIR/HabEx and the Origins Space Telescope (OST).

May 10, 2018
noon - 1 p.m.
3853 Slichter

Presented By:

• Emily Hawkins - UCLA

The magnetic fields of planets are generated and sustained by fluid motions in their electrically conducting liquid metal interiors. The key characteristics of such flows, thought to be governed to leading order by rapid rotation and turbulent convection, are not well understood at present. Our new laboratory device, ‘NoMag’, is designed to span a wider and more extreme range of parameters than previously studied, thus allowing us to explore essential features of rotating convection in a setting similar to that of core flows, i.e. one that is both rapidly rotating and highly turbulent. Specifically, ‘NoMag’ is constructed to simulate a local, polar parcel of planetary core convecting fluid under the influence of axial rotation and buoyancy forcing. As such, a cylindrical geometry is constructed with a fixed diameter of D ≈ 60 cm and heights ranging between H ≈ 5 cm to H ≈ 185 cm. Using this device, we explore the properties of rotating convection in water, with Ekman numbers (viscous diffusion/Coriolis force) ranging between E ≅ 3×10−8 (i.e. rapidly rotating) to E ≅ 10−3 (i.e. weakly rotating) and Rayleigh numbers (thermal buoyancy/ thermal and viscous diffusion) between Ra ≅ 105 (i.e. weakly convecting) to Ra ≅ 1013 (i.e. turbulently convecting). We utilize laser doppler velocimetry (LDV) to obtain point measurements of bulk convective velocities, resulting in measured Reynolds numbers (inertia/viscous diffusion) ranging between Re ≅ 102 to Re ≅ 5 × 104 , with the onset of turbulence occurring near Re ∼ O(103 ). For the first time, we couple velocity and heat transfer measurements by the simultaneous collection of temperature time series at the fluid boundaries and at multiple locations within the fluid bulk. In this talk, I will present recent experimental results using our H ≅ 20 cm tall tank that test inevitably coupled heat transfer and convective velocity scaling predictions relevant to rapidly rotating systems.

May 10, 2018
noon - 1 p.m.
3853 Slichter

Presented By:

• Ashna Aggarwal - UCLA

The azimuthally-directed zonal winds of the gas giants, Jupiter and Saturn, are amongst their most dominant surface features. Recent Juno gravity measurements have inferred that the zonal winds of Jupiter extend from the weather layer where they are observed down at least 3,000 km deep into the H-He molecular atmosphere. In addition, Jupiter’s electrical conductivity increases as a function of spherical radius, r, as the molecular envelope transitions to a liquid metal. As electrical conductivity increases, the strength of magnetic forces grows, which act as a resistive brake on the azimuthal jet flows. The process of magnetic braking, thought to play a key role in the spherical truncation of the jets, will be quantified with this study. As such, I have developed a pseudo-spectral code that solves the Cartesian Navier-Stokes equations in 2-D with buoyancy and a quasi-static magnetic field. I conduct di- rect numerical simulations (DNS) of shearing convection and vary the strength of the imposed magnetic field, whose intensity is controlled by the value of the Chandrasekhar number, Q, (estimated ratio of Lorentz and viscous forces) in order to investigate the effects of a magnetic field on the damping of the shear flow. In this talk, I will present preliminary results of the first magneto-hydrodynamic case, carried out at Rayleigh number, Ra = 106 (the ratio of buoyancy to diffusion), Prandtl number, Pr = 1 (the ratio of viscous to thermal diffusion), and Q = 103 , where the jet flows are strongly magnetically damped

May 17, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Jing Luan - Univeristy of California Berkeley

Enceladus is one of the most popular worlds that might accommodate life outside our own earth. We study its evolutionary path, especially focus on the physical processes that drive Enceladus to its current state. I will also discuss possible applications of these physical processes to other bodies in our solar system. Below is a brief summary of the evolution path for Enceladus. Eccentricity (e) growth as Enceladus migrates deeper into mean motion resonance with Dione results in increased tidal heating. As the bottom of the ice shell melts, the rate of tidal heating jumps and runaway melting ensues. At the end of run-away melting, the shell's thickness has fallen below the value at which the frequency of free libration equals the orbital mean motion and e has damped to well below its current value. Subsequently, both the shell thickness and e partake in a limit cycle. As e damps toward its minimum value, the shell's thickness asymptotically approaches its resonant value from below. After minimum e, the shell thickens quickly and e grows even faster. This cycle is likely to have been repeated multiple times in the past. Currently, e is much smaller than its equilibrium value corresponding to the shell thickness. Physical libration resonance resolves this mystery, it ensures that the low-e and medium-thickness state is present for most of the time between consecutive limit cycles. It is a robust scenario that avoids fine tuning or extreme parameter choice, and naturally produces episodic stages of high heating, consistent with softening of topographical features on Enceladus.

May 24, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Mathieu Choukroun - JPL

Seminar Description coming soon.

May 31, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Ashley Shoenfeld - UCLA
• Akash Gupta - UCLA

Seminar Description coming soon.

June 7, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• David Paige - UCLA

Seminar Description coming soon.