Planetary Science Seminar - Winter-2018

Jan. 11, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• An Yin - UCLA

Full Title: A gravity-scaled fracture-formation model and its applications to explain the giant polygons (30-80 km) on Pluto.

Polygon terrains have been observed on the surfaces of many solar system bodies with their horizontal dimensions increasing with surface gravity: polygon dimensions are generally <10s m on Earth (e.g., ice-wedge polygons and mud cracks) but are ~30 km and even up to 80 km on Pluto that has a small surface gravity g = 0.62 m/s2. Assuming that the commonly observed 1:5 scaling on Earth applies to all planetary bodies, the thermal contraction mechanism for the formation of Pluto polygons has been ruled out because the polygon layer thickness on Pluto is believed to be too thin (<500 m) to create the large dimensions of polygons 10s km across. In this talk, I present a new two-layer model that scales fracture spacing with gravity. The model results show that the dimension of polygon size increases exponentially with surface gravity, viscosity of the basal shear zone below the contracting layer, and the shear strain rate. Using the realistic rheological parameters for nitrogen ice, the model explains well the size of the giant polygons observed on Pluto.

Jan. 18, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Eve Lee - Caltech

Sub-Neptunes around FGKM dwarfs are evenly distributed in log period down to ~10 days but dwindle in number at shorter orbital periods. I will demonstrate how magnetospheric truncation of disks and tidal inspiral of planets are responsible for sculpting this orbital architecture. Both the break at ~10 days and the slope of the occurrence rate down to ~1 day can be reproduced if planets form in disks that are truncated by their host star magnetospheres at co-rotation. Planets can be brought from disk edges to ultra-short (<1 day) periods by tides raised on their stars. Tidal migration can explain why these ultra-short period planets (USPs) are more widely spaced than their longer period counterparts. Planets around metal-rich stars occupy a wider range of orbital periods and planetary radii. I will discuss how pre-main sequence stellar evolution and the evolution of solid disks can give rise to the diversity of planets seen around metal-rich stars.

Jan. 25, 2018
noon - 1 p.m.
3853 Slichter

Presented By:

• Ruth Murray-Clay - UCSC

What sets the extent of giant planet formation, and what does this tell us about the structures of planetary systems in general? I will provide evidence that observed disks may be more massive than previously thought, suggest that disk evolution may set the inner scale of giant planet formation, and show that gas turbulence coupled with pebble accretion may set the largest distances at which giant planets form. Finally, a class of solar system analogs has yet to be identified among the large crop of planetary systems now observed. I will suggest that the solar system's structure is representative of the lowest-metallicity systems that nevertheless host giant planets.

Feb. 1, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Juan Lora - UCLA

Saturn’s moon Titan hosts a massive nitrogen atmosphere with a vigorous circulation, and sustains an exotic but recognizable hydrologic cycle in which methane is the primary condensible. With the goal of understanding essential observed features of Titan’s climate system, I will discuss the Titan Atmospheric Model, the general circulation model that most accurately simulates the middle and lower atmosphere. I will demonstrate how we use data-model comparisons to gain fundamental insights into Titan’s seasonal circulation, distinct climate zones, and global hydrologic cycle. Finally, I will discuss ongoing work investigating other planetary atmospheres, including applying our growing knowledge of Titan and versatile climate modeling to addressing exoplanetary regimes.

Feb. 8, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Dimitri Mawet - Caltech

In this talk, I will first review the state of the art in direct imaging and spectroscopic characterization of giant exoplanets using ground-based adaptive optics (AO) systems. I will highlight recent high-impact scientific results and the techniques and technologies that enabled them. In the second part of this talk, I will describe our recent study quantifying the occurrence rate of giant planets in dusty systems, demonstrating that debris disks are bona fide signposts to long-period giant exoplanets. As a case in point, I will present the results of our new joint radial velocity and direct imaging exploration of the emblematic but curious case of the Epsilon Eridani planetary system, using Lick and Keck archival RV data and the NIRC2 L and M-band vortex coronagraph. The new coronagraph is the first step towards the Keck Planet Imager and Characterizer (KPIC) facility currently being deployed at W.M. Keck Observatory. I will conclude this talk by a status update of this four-pronged upgrade to the Keck AO system and instrument suite that is entirely dedicated to the deep exploration of exoplanetary systems with direct techniques.

Feb. 15, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Jim Fuller - Caltech

Gravity waves are low frequency fluid oscillations restored by buoyancy forces in planetary and stellar interiors. Despite their ubiquity, the importance of gravity waves in evolutionary processes and asteroseismology has only recently been fully appreciated. I will discuss gravity waves in two very different astrophysical contexts: the interiors of giant planets and the cores of red giant stars. Gravity modes appear to have been detected in the planet Saturn using its rings as a seismograph, revealing crucial details about the evolution of giant planets. These modes could also be responsible for the outward tidal migration of giant planet moons. Kepler asteroseismic data has revealed gravity modes in thousands of red giant stars, providing measurements of core rotation that are faster than the surface rotation, but slower than expected. Moreover, gravity modes (or lack thereof) can reveal strong magnetic fields in the cores of red giants, and strong fields appear to be common within "retired" A stars. I will discuss the implications of these results for compact remnants of all types.

Feb. 22, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Matthew Tiscareno - SETI Institute

assini ended its spectacular 13-year mission at Saturn with a two-part farewell, during which it obtained the sharpest and highest-fidelity images ever taken of Saturn’s rings. From December 2016 to April 2017, the spacecraft executed 20 near-polar orbits that passed just outside the outer edge of the main rings; these “Ring-Grazing Orbits” provided the mission’s best viewing of the A and F rings and the outer B ring. From April to September 2017, the spacecraft executed 22 near-polar orbits that passed between the innermost D ring and the planet’s clouds; this “Grand Finale” provided the mission’s best viewing of the C and D rings and the inner B ring. We will review the discoveries made by high-resolution imaging of the main rings during these maneuvers. Topics will include: 1) Sharply defined belts with differences in degree and character of clumpiness, which are probably an index for particle properties and interactions; 2) Unprecedentedly detailed images of propellers, which are local disturbances in the ring created by an embedded moon; and 3) Abundant color images of impact ejecta clouds, which constrain the population of decimeter-to-meter-sized meteoroids in Saturn’s vicinity as well as the particle-size distribution of the ejecta, and thus the fracture properties of ring material.

March 1, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Anton Ermakov - JPL

In the 2020’s, spacecraft are planned to visit a diverse selection of minor bodies with sizes from hundreds of meters to hundreds of kilometers. These spacecraft include NASA’s OSIRIS-REx, Psyche and Lucy as well as JAXA’s Hayabysa-2 and MMX missions. In this talk, I will discuss the main geophysical results of the Dawn mission in its exploration of asteroid Vesta and dwarf planet Ceres and how this knowledge could inform the future missions.

March 8, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Ned Wright - UCLA

I will talk about one balloon telescope and four space missions I have been involved with (COBE, WMAP, Spitzer & WISE) that have all made planetary observations. The all-sky survey missions COBE, WMAP and WISE have large data archives that are certainly not all mined out, and I will show several examples based on the NEOWISE archive. Finally I will discuss NEOCam, and proposed missions dedicated to an IR survey for asteroids.

March 15, 2018
noon - 1 p.m.
Slichter 3853

Presented By:

• Renyu Hu - JPL

Seminar Description coming soon.