Category: Seminars

I present some novel insights based on first principles, parameterized 1D thermal history, and 3D spherical mantle convection evolution models, which raise doubt concerning many crucial assumptions commonly used in planetary geodynamics and allow for a new view on the thermal and tectonic evolution of rocky planets in our solar system and beyond.

The new approach leads to massive rocky planets (Earth and bigger) remaining hotter for longer and plate tectonics being ideally initiated early on in the first 0.1-1Gyr driven by core cooling and boosted by a dry mantle and a late delivery of oceans. The latter suggests that geodynamically the early Earth might have been in many ways similar to today and connects the origins of plate tectonics to planet formation. For Venus, the high surface temperatures and a lack of surface oceans allow to initiate but not to maintain plate tectonics – suggesting an unstable tectonic configuration.

This evolutionary interior and tectonic framework also opens a door to systematically connect geodynamics to the evolution of metabolic pathways and the origins of life. In this context, I show preliminary results on the time-dependent (and for Mars and Earth local) geodynamic formation of hydrogen and methane rich oases.

Detecting polarized light from self-luminous exoplanets has the potential to provide key information about rotation, surface gravity, cloud grain size, and cloud coverage. While field brown dwarfs with detected polarized emission are common, no exoplanet or substellar companion has yet been detected in polarized light. With the advent of high contrast imaging spectro-polarimeters such as GPI and SPHERE, such a detection may now be possible with careful treatment of instrumental polarization. I will discuss the role of polarimetry in brown dwarf and exoplanet science, test observations with GPI, as well as current and future polarimetric observing campaigns.

Many hot Jupiter systems exhibit significant misalignment between the orbital axis of the planet and the spin axis of its host star. While this misalignment could be primordial in nature, a large fraction of hot Jupiters are found in systems with distant stellar companions, and thus could have undergone Lidov-Kozai (LK) oscillations and acquired their misalignment dynamically. Here we present a study of the effect of spin-orbit coupling during LK oscillations, and the resulting spin-orbit misalignment angle distributions. We show that spin-orbit coupling induces complex, often chaotic, behavior in the spin axis of the host star, and that this behavior depends significantly on the mass of the planet and the properties of the host star (mass and spin history). We develop a semi-analytical framework that successfully explains most of the possible stellar spin behaviors. We then present a comprehensive population synthesis of hot Jupiters created via the LK mechanism, and discuss their possible observable signatures.

I will present the results from a survey of stars with “holey debris disks”, two-belt debris disks, in the southern hemisphere. I will briefly summarize the image processing techniques used to directly image these targets. We demonstrate that these disks with holes are good targets for directly detecting planets with the discovery of a planet around two of our targets, HD 95086 and HD 106906, at L’-band. The detected planets likely shepherd the outer cool debris belt. The relatively dust-free gap in these disks implies the presence of one or more closer-in planets. I will discuss our continued search for planets around promising new targets using Keck and the vector vortex coronagraph.

Phobos, the inner, asteroid-like satellite of Mars, is only 20 km diameter yet exhibits a perplexing geology. Orbiting well inside the corotation radius, and also inside the Roche limit, it will spiral into Mars in a few ten million years, and experiences increasing tidal deformation. Several features stand out: the crater Stickney, almost 10 km diameter, and complex networks of striations and pitted grooves. This talk will emphasize our recent work, that shows that the patterned striations are formed by the distortion of a weak elastic shell overlying an even weaker deformable interior (Hurford et al., in review) and that the pitted grooves are sesquinary catenae formed by the eventual re-impact of ejected material (Nayak and Asphaug, in review). Long considered a possible outpost for human exploration, Phobos has a continually active geology that would be hazardous. Deimos, farther from Mars and not experiencing increasing tides, is a safer venue.

The moons of Mars, Phobos and Deimos, are high priority targets for future exploration by both robotic and human missions. Despite decades of study by ground and Mars-orbiting spacecraft, key questions about the moons’ origin, geologic evolution, and potential to provide in situ resources for future manned missions remain unresolved. Phobos and Deimos either formed in situ around Mars through co-accretion or giant impact, or they are captured asteroids that originated from elsewhere in the solar system. One key to unlocking this mystery will be to determine whether the moons are composed of materials expected to be native to Martian system or if they are made of something more exotic that more likely would have been introduced from another location. Determining Phobos’ and Deimos’ surface compositions remotely has proven to be challenging in part because they lack strong diagnostic absorption features and in part because spectral observations of the moons are acquired at a variety of lighting conditions, which makes it difficult to compare them to laboratory spectra of well-characterized samples collected under controlled lighting conditions. I will present analyses of spectral data that address both of these challenges and demonstrate the moons are likely composed of volatile-rich, carbonaceous-chondrite like material, supporting the idea that they are captured asteroids from the outer solar system. I will also discuss the importance and benefits of future in situ exploration to address some of the many remaining questions about these fascinating solar system bodies.

Vast resources have been dedicated to characterizing the handful of planets with radii between Earth’s and Neptune’s that are accessible to current telescopes. Observations of their transmission spectra have been inconclusive and do not constrain the atmospheric composition. Of the small planets studied to date, all have radii in the near-IR consistent with being constant in wavelength, likely showing that these small planets are consistently enshrouded in thick hazes and clouds. I will explore the types of clouds and hazes that can completely obscure transmission spectra. I will then show the effect that these thick clouds have on the thermal emission and reflected light spectra of small exoplanets. I present a path forward for understanding this class of small planets: by understanding the thermal emission and reflectivity of small planets, we can potentially break the degeneracies and better constrain the atmospheric compositions.

With the advent of powerful space-based infrared telescope facilities,
we are seeing a surge in the number of cometary nuclei whose thermal
emissions are being measured. This work has the potential to provide
insight into the ensemble structural and thermophysical properties
of comets and, ultimately, the circumstances of their formation and
evolution. Moreover, these studies are now happening while the
Rosetta spacecraft continues its detailed and lengthy study of comet
67P, giving us excellent context with which to try to understand
the wealth of remote observations of other comets. This is important
since for the forseeable future there will always be far more comets
observed remotely than in-situ, and we must understand what such
data are telling us about nuclei and near-nucleus comae so that we
are not fooled into misinterpretation. I will review some recent,
key results on cometary physical properties and on what we might
think of as a “typical” comet. I will also discuss some unanswered
questions that should be addressed in the future, and what the
observational limitations and opportunities are with regard to them.

As we mark the twentieth anniversary of the discovery of the first planet orbiting another Sun-like star, the study of extrasolar planets is maturing beyond individual discoveries to detailed characterization of the planet population as a whole. No mission has played more of a role in this paradigm shift than NASA’s Kepler mission. Discoveries from the prime Kepler mission demonstrated that small planets (< 3 Earth-radii) are common outcomes of planet formation around G, K, and M stars. While Kepler detected many such planets, all but a handful orbit faint, distant stars, which are not amenable to precise follow up measurements. NASA’s K2 mission has the potential to increase the number of known small, transiting planets around bright stars by an order of magnitude. I will present the latest results from my team’s efforts to detect, confirm, and characterize planets using the K2 mission.

I’ll present a brief overview of the Thirty-Meter-Telescope project, whose construction on top of Mauna Kea is scheduled to take about eight years, with first-light currently planned for the horizon 2023/24, and start of science operations soon after. I’ll review the expected observing performances of the facility and its first-light instruments, which will combine imaging and spectroscopic capabilities, along with powerful adaptive-optics corrected wavefronts and the use of a laser-guide-star facility in some cases. TMT will enable ground-based exploration of our solar system – and planetary systems at large – at a dramatically enhanced sensitivity and spatial resolution across the visible and near-/thermal- infrared regimes (e.g. ~7km spatial resolution at a wavelength of 1micron on main-belt asteroids, 20km on Galilean satellites, 40km on Titan, etc). TIO operations will meet a wide range of observing needs and the implementation of science programs will take into account the stringent observing time constraints often encountered for observations of our solar system such as, for instance, the scheduling of target-of-oportunity observations, the implementation of short observing runs, or the support of long-term “key-science” programmes.