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Planetary Science Seminar - winter-2024

The Cosmic Prevalence of Resonance

Jan. 11, 2024
noon - 12:50 p.m.
3853 Slichter Hall

Presented By:

  • Professor James Fuller - Caltech
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Resonances are well known to be important in orbital dynamics, but their impacts are being seen in surprising new ways. In the Saturn system, resonances between planetary oscillation modes and the rings allow us to perform seismology of Saturn. Planetary oscillation modes also resonate with the moons to drive their orbital migration, causing them to enter orbital resonances with each other. A similar process likely operates in exoplanet systems, where resonances between stellar oscillation modes and short-period planets can cause them to migrate inwards or outwards. Finally, resonances between the spin precession and orbital precession rates of three-body stellar systems can drive stars into a Cassini state, creating a new class of strange, slowly spinning stars.

Dehydration of rocky interiors leads to vastly different oceans on planetary bodies: Europa, Ceres and Titan as case studies, and implications for habitability

Jan. 18, 2024
noon - 12:50 p.m.
3853 Slichter Hall

Presented By:

  • Dr. Mohit Melwani Daswani - Jet Propulsion Laboratory
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The origin of the oceans of icy ocean worlds in our solar system (and now beyond) became a topic of intense research since NASA’s Galileo mission got a close look at Europa’s frozen, young surface. Recent studies (Melwani Daswani et al., 2021; Mousis et al., 2023) attempting to understand the origin of Europa’s ocean have shown that solid reservoirs of volatiles, such as phyllosilicates and other volatile-bearing minerals, could provide a one-way path towards the formation of oceans on bodies that may have accreted in a water-poor environment. Carbon dioxide resulting from the breakdown of carbonates may well have been observed by the James Webb Space Telescope recently at the surface of Europa (Trumbo and Brown 2023; Villanueva et al., 2023). Using thermodynamic models, here we focus on the cases of Europa, Titan and Ceres, and how they evolved into very different ocean worlds, as hydrated minerals in their rocky interiors destabilized and released their locked up volatiles during thermal metamorphism excursions caused by tidal dissipation or radioactive decay. Fluids generated in the interiors may transport solutes (CHNOPS, redox-sensitive species, metals, etc.). Thus, fluids flushed out of rocky interiors and into oceans, directly affect habitability. How widespread could this process be, and could the signatures of such a process be observed by future in-situ missions like Europa Clipper or Dragonfly?

Climate Regimes Across the Habitable Zones of Dim Stars

Jan. 25, 2024
noon - 12:50 p.m.
3853 Slichter Hall

Presented By:

  • Dr. Ana Lobo - UC Irvine
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In the race to detect life beyond the Solar System, rocky M- and K-dwarf planets are increasingly observable and offer exciting prospects. Climate studies of these planets often assume an ocean-covered world. However, M-dwarf habitable zone planets may struggle to acquire and retain water throughout their lifetimes due to enhanced heating and high-energy radiation during early stellar evolution, and persistent stellar flares, such that water-limited land planets may be especially common. Land planets can have uniquely diverse climates, with large temperature gradients. Our recent work shows that, unlike aquaplanets, they can be in a "terminator habitability" climate regime. With scorching dayside and freezing nightside temperatures, their habitable surface areas are confined to the terminator. These results, combined with observational advantages for arid planets, indicate that land planets will be attractive candidates for early detections of habitability. In this talk, we will take a tour of the M- and K-dwarf habitable zones to explore the climates of aquaplanets and land planets, and their prospects for near-future climate characterization and habitability.

Exoplanet Atmospheres — From Photochemistry to Habitability

Feb. 1, 2024
noon - 12:50 p.m.
3853 Slichter Hall

Presented By:

  • Dr. Shang-Min Tsai - UC Riverside
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Abstract: Exoplanet science has progressed rapidly in the past decade. It has transitioned from the era of detection to characterization. The sheer diversity of exoplanets broadens our understanding of planetary science and offers profound insights into the evolution of our own world. The observational advancement allows us to probe the atmosphere of giant exoplanets in detail. In this talk, I will discuss how we study the makeup of atmospheres using spectroscopy and numerical models. I will highlight our recent work on WASP-39 b from the JWST Early Release Science (ERS) program, where we discovered the first evidence of photochemistry on an exoplanet in a wonderfully unanticipated way. I will discuss the climate and habitability of the most common class of planets, known as sub-Neptunes, which curiously find no analogues in our own solar system. I will explore my recent work on the habitability and biosignatures of some of these temperature sub-Neptunes. In closing, I will provide an outlook on the future prospects of observing and modeling exoplanetary atmospheres. Biographical Sketch: I am currently a postdoc in the Earth and planetary sciences at UC Riverside. Originally from Taiwan, I did my undergraduate degree in Physics and my master's degree in astrophysics at National Taiwan University in Taipei. For my Ph.D. (2014 -- 2018), I worked with Prof. Kevin Heng and developed the first open-source photochemical model for exoplanets "VULCAN." In December 2018, I moved to the UK to work with Prof. Raymond Pierrehumbert on various climate-related topics at the University of Oxford. My main interest is the atmospheric chemistry and climate dynamics of planetary and exoplanetary atmospheres.

UV Raman and Fluorescence Spectroscopy for Astrobiology on Mars

Feb. 8, 2024
noon - 12:50 p.m.
3853 Slichter Hall

Presented By:

  • Dr. Sunanda Sharma - Jet Propulsion Laboratory
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Mars is a primary target for astrobiology investigations given evidence for habitable conditions in its past and, possibly, in its present. The Mars 2020 Perseverance rover is currently exploring the Margin region of Jezero crater, Mars. Jezero crater, once a potentially habitable lake, now hosts a wide array of minerals, including those with high organic and biosignature preservation potential. SHERLOC (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals) is one of seven scientific instruments aboard Perseverance. SHERLOC has multiple components: a deep UV Raman and fluorescence spectrometer, a context imager, and an accompanying high-resolution color imager. Together, these techniques allow SHERLOC to map possible organics and minerals in place on a rock surface, which is important for understanding how organics and potential biosignatures may have been formed, transported, or concentrated on Mars. The presence, type, and distribution of organic carbon has implications for the habitability of an environment. Here, I will share some of the current mission results, relevant laboratory data from SHERLOC analog instruments, and the implications for our understanding of habitability and astrobiology on Mars.

Unexpected Variability in Multi-Year Cycles of Jupiter’s Temperatures and Aerosols from Ground-Based Thermal Infrared Imaging

Feb. 15, 2024
noon - 12:50 p.m.
3853 Slichter Hall

Presented By:

  • Dr. Glenn Orton - Jet Propulsion Laboratory
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An essential component of planetary climatology is knowledge of the atmospheric temperature and particulate fields and their variability. This study used a large set of ground-based mid-infrared images obtained between 1984 and 2019 to characterize long-term changes in Jupiter’s temperature and aerosol fields. This long baseline allowed us to detect variability that was distinct from seasonal variability that would be correlated with Jupiter’s 11.7-year orbital period. Previous studies of Jupiter hinted at non-seasonal periodic behaviour, as well as the presence of a dynamical relationship between tropospheric and stratospheric temperatures. However, these observations were made over time frames shorter than Jupiter’s orbit or they used sparse sampling. This extensive data set has enabled us to derive temperatures from the upper troposphere (500 mbar) to the lower stratosphere (30 mbar), and upper-tropospheric (400-600 mbar) aerosol opacity. Periodicities of 4, 7–9 and 10–14 years were discovered in tropospheric temperatures that involve different latitude bands and seem disconnected from seasonal changes in solar heating. Anticorrelations of variability in opposite hemispheres were particularly striking at 16°, 22° and 30° from the equator. We also discovered that a thermal oscillation present in Jupiter's equatorial stratosphere at the 10-mbar pressure level (known as Jupiter’s Equatorial Stratospheric Oscillation) is also observed to descend to higher pressures (330 mbar), meaning that it is not confined to the stratosphere and suggests a top-down control of equatorial tropospheric temperatures from stratospheric dynamics. We observe that the northern mid-latitudes poleward of 30° are continuously warmer than their counterpart latitudes in the south at 10 mbar pressure level (the stratosphere), most likely due to differences in radiative heating by Jupiter’s polar haze, which extends to lower latitudes in the north compared to the south. We also note the presence of a lag between temperature and aerosol changes at diverse latitudes and use this to identify the mechanisms responsible for the different atmospheric disturbances observed on Jupiter. Realistic future global climate models must address the origins of these variations in temperatures and aerosols in preparation for their extension to a wider array of gas-giant exoplanets.

Numerical Modeling of Zonal Winds on Gas Giants

Feb. 22, 2024
noon - 12:50 p.m.
3853 Slichter Hall

Presented By:

  • Dr. Paula Wulff - MPS
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The outer regions of both Jupiter and Saturn host strong, alternately eastward and westward zonal winds. These are essentially steady in time and cover all latitudes, albeit diminished in amplitude at the mid-to-high latitudes. Gravity measurements have revealed that the jets observed on the surface must extend deep into the planets’ convective regions, from the surface to around 3,000 km and 9,000 km in Jupiter and Saturn respectively. Numerical simulations have had difficulties in reproducing winds that form at the higher latitudes and are quenched at these inferred depths, in the same models. This talk addresses this conundrum and shows that the key structural element is a stably stratified layer, located below the outer convective region where zonal winds form. In this layer, radial flows are inhibited and convection is quenched which leads to a damping of zonal winds and a decoupling from underlying conducting regions. It is found that wider jets penetrate further into the stable layer and the structures are no longer invariant with respect to the axis of rotation, as they are in the rotationally dominated convective envelope. Furthermore, magnetic effects, quantified by the electrical conductivity and the internal magnetic field, can reduce the penetration depth of the jets. Our simulations suggest that the presence of stable stratification that reaches upwards into a region of weak conductivity is essential for maintaining strong winds at mid-to-high latitudes, that drop off at a depth that is consistent with constraints from the measured gravity and magnetic fields.

Planet Nine From Outer Space: a Status Update + New Evidence

Feb. 29, 2024
noon - 12:50 p.m.
3853 Slichter Hall

Presented By:

  • Professor Konstantin Batygin - California Institute of Technology
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Over the past two decades, observational surveys have progressively unveiled the complex orbital structure of the Kuiper Belt, revealing a myriad of icy bodies orbiting the Sun beyond Neptune. While many orbital behaviors within this region adhere to predictions based on the known eight-planet Solar System, a distant portion of the trans-Neptunian object (TNO) census exhibits dynamics that defy explanation. Notably, the physical clustering of orbits with semi-major axes exceeding ∼ 250 AU, the detachment of perihelia of certain Kuiper belt objects from Neptune's influence, and the mysterious origins of highly inclined/retrograde long-period orbits pose significant challenges to the conventional Solar System model. The peculiar dynamical architecture of these distant solar system objects suggests the presence of a yet-undetected planet, estimated to have a mass M9 ∼ 5M⊕, orbiting on moderately inclined orbit with a semi-major axis a9 ∼400−800 AU and eccentricity e9 ∼ 0.2−0.6. In this talk, I will review the observational evidence and dynamical arguments that underpin this hypothesis, and introduce a new line of evidence that further substantiates the case for Planet Nine.

Exploring the Regolith of Jezero Crater, Mars

March 14, 2024
noon - 1 p.m.
3853 Slichter Hall

Presented By:

  • Dr. Emily Cardarelli - University of California, Los Angeles
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The Mars 2020 Perseverance rover successfully landed in Jezero crater, Mars in February 2021. From the Octavia E. Butler landing site, the rover began its mission to explore and sample an ancient crater lake basin, seeking signs of ancient microbial life. Perseverance has explored and sampled multiple geologic units of Jezero crater over the past 1000+ sols. Two regolith (i.e. unconsolidated sediments ranging in grain size and rock fragments) samples have also been acquired within the Delta Front unit during this time. In this talk, I delve into the regolith encountered over multiple campaigns from a multi-instrument perspective. The Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument is a deep UV Raman and fluorescence spectrometer, context imager, and high-resolution camera combined, which enables high-resolution imaging and spectroscopic analysis of multiple mineral classes and potential organic compounds. Linking SHERLOC observations with the stereoscopic, zoomable, and multispectral Mast Camera Zoom (Mastcam-Z) instrument observations provides greater geologic context and facilitates the calculation of key regolith parameters. These combined observations reveal diverse grain types, a range of grain sizes, and multiple populations of grains – some of which link to nearby rocks and were acquired for eventual return to Earth via the Mars Sample Return mission.