Planetary Science Seminar - fall-2019

Oct. 3, 2019
noon - 1 p.m.
Slichter 3853

Presented By:

• Bryce Bolin - Caltech

Asteroid families are the remnant fragments of asteroids broken apart by collisions, and only a few are known to be older than 2 Ga. We use a novel family identification technique sensitive to >2 Ga-old families to discover a 4 Ga-old family linking most dark asteroids in the inner Main Belt. The 4 Ga-old family reveals asteroids with D > 35 km that do not belong to any asteroid family implying that they originally accreted from the protoplanetary disk.

Oct. 10, 2019
noon - 1 p.m.
3853 Slichter

Presented By:

• Yasuhiro Hasegawa - JPL

The origin of Jovian planets in both the solar and extrasolar systems is still elusive. The recent significant progress of astronomical observations and NASA's Juno mission has opened up invaluable opportunities of answering to this long-standing problem. In this talk, I will explore the origin of the total heavy-element content of Jovian planets. Making use of the existing semi-analytical formulae of accretion rates of pebbles and planetesimals, I will show that the total heavy elements inferred both for Jupiter and giant exoplanets would originate from solid accretion at the final stage of giant planet formation. In the stage, proto-jovian planets accrete solids from gapped planetesimal disks, and gas accretion is limited by disk evolution. I will also apply this finding to identifying the main formation site of these planets, and show that the plausible region may locate at r > 0.6 au, implying the importance of planetary migration. The combination of these efforts may enable us to move towards a comprehensive understanding of giant planet formation.

Oct. 17, 2019
noon - 1 p.m.
Slichter 3853

Presented By:

• David Ardilla - JPL

The small satellite industry is experiencing a boom, with over 7,000 satellites predicted to be launched by 2027. Small satellites (SmallSats) have performed missions in planetary science, heliophysics, and Earth science. Within astrophysics, the use SmallSats remains limited and I explore the reasons behind the lack of astrophysics SmallSats. I discuss SPARCS, the Star-Planet Activity Research CubeSats, a SmallSat that will study variability in M-dwarfs in order to understand planet habitability. I address opportunities available for using SmallSats for Exoplanet Science, as well as technology gaps that need to be closed in order to fully exploit the new opportunities.

Oct. 24, 2019
noon - 1 p.m.
Slichter 3853

Presented By:

• Lars Stixrude - UCLA

The intrinsic luminosity of Uranus is a factor of 10 less than that of Neptune, an observation that standard giant planetary evolution models, which assume negligible viscosity, fail to capture. Here we show that more than half of the interior of Uranus is likely to be in a solid state, that the viscosity of this region is large (>1014 Pa s), and that thermal evolution models that account for this high viscosity region satisfy the observed faintness of Uranus by storing accretional heat deep in the interior. A frozen interior also explains the quality factor of Uranus required by the evolution of the orbits of its satellites.

Oct. 31, 2019
noon - 1 p.m.
Slichter 3853

Presented By:

• Renata Frelikh - UCSC

I will talk about the origins of eccentric warm Jupiters discovered via the radial-velocity method. An important clue for their dynamical histories has not yet been explained: most of these planets with high eccentricities (e > 0.6) tend to also be planets of higher mass (m > 1 MJ). Furthermore, these eccentric planets are preferentially found around stars that are metal-rich. I will describe how these eccentricities can arise in a phase of giant impacts, which I model with n-body simulations to show that (1) the high-eccentricity giants observed today may have formed preferentially in systems of higher initial total planet mass, and (2) the upper bound on the observed giant planet eccentricity distribution is consistent with planet-planet scattering. Finally, I will describe a proof-of-concept for how the systems present in our giant impacts model can be created via pebble accretion.

Nov. 7, 2019
noon - 1 p.m.
Slichter 3853

Presented By:

• Paul Rimmer - University of Cambridge

Recent geological evidence suggests that the early Earth suffered a single impact from a moon-sized object about 4.3 billion years ago. This impact would have transformed the early atmosphere into a transient Miller-Urey atmosphere, dominated by H2, CO, CH4 and N2/NH3, an ideal environment for prebiotic chemistry. It is likely that Mars also experienced a single large impact early on, transforming its early atmosphere as well. Some exoplanets may be following a similar path to Earth and Mars, suffering one large impact and then several smaller impacts, leaving behind molecular signatures of these events. I take results from impact simulation experiments, and apply them to atmospheric chemistry and radiative transfer models to predict the molecular signatures of these events. I show that acetylene (C2H2) is produced effectively by impacts, and not by photochemistry, in potentially detectable quantities on impact-transformed planets.

Nov. 14, 2019
noon - 1 p.m.
Slichter 3853

Presented By:

• Akash Gupta and Allie Doyle - UCLA

ALLIE DOYLE: Abstract: Studies of exoplanets are on the rise, and we want to constrain the geochemistry of the rocky exoplanetary bodies. Using white dwarf stars that are polluted by rocky exoplanetary material, we have measured the oxidation state of ~15 of these bodies. The oxidation state, as measured by its bulk oxygen fugacity (fO2), is a critical factor that determines a planets structure and evolution. The intrinsic oxygen fugacity of a planet can determine the relative size of its metallic core, the geochemistry of its mantle and crust, the composition of its primordial atmosphere, and the forces responsible for mountain building. Most rocky bodies in our solar system formed with oxygen fugacities approximately five orders of magnitude higher than that corresponding to a hydrogen-rich gas of solar composition. We find that the intrinsic oxygen fugacities of rocks accreted by polluted white dwarf stars are similar to those of terrestrial planets and asteroids in our solar system. This result suggests that at least some rocky exoplanets are geochemically, and could be geophysically, similar to Earth. AKASH GUPTA: Abstract: In the last decade, NASA's Kepler mission has revolutionized the field of planetary science by discovering more than 4000 planetary candidates. As one of its key findings, it revealed that the most common planets, observed to date, are of the size 1 to 4 Earth radii in size. Interestingly, further observations have revealed a 'radius valley' in the size distribution of small, short-period exoplanets, i.e., a lack of planets of the size 1.5 to 2 Earth radii (by a factor of ~2). Furthermore, studies have observed that smaller planets (<1.5 Earth radii) have higher densities consistent with rocky compositions while larger planets (>2.0 Earth radii) have lower densities, suggesting they are engulfed in significant H/He atmospheres. Typically, this radius valley has been attributed to atmospheric mass-loss because of photoevaporation due to high energy radiation from host stars. However, in recent work, it has been demonstrated that atmospheric mass-loss, powered by the cooling luminosity of the planetary core, can explain this radius valley in the exoplanet size distribution, even without photoevaporation. In my talk, I will describe the key physical processes that drive this core-powered mass-loss mechanism and discuss our recent work where we present comparisons with a multitude of latest observations and present testable predictions for the core-powered mass-loss mechanism as a function of stellar mass, metallicity and age.

Nov. 21, 2019
noon - 1 p.m.
Slichter 3853

Presented By:

• Lior Rubanenko - UCLA

Permanently shadowed craters near the poles of Mercury and the Moon harbor water ice inside cold-traps, which are among the coldest places in the solar system. Despite their similar thermal environments, past telescopic and remote sensing observations have found cold-traps on Mercury contain significantly more ice than cold-traps on the Moon. We use remote sensing techniques coupled with models to investigate this surprising difference and probe the physical properties of the ice to learn about its potential origin.

Dec. 5, 2019
noon - 1 p.m.
Slichter 3853

Presented By:

• Emily Hawkins - UCLA

Seminar Description coming soon.