Katherine de Kleer

Assistant Professor | Division of Geological and Planetary Sciences | Caltech

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Recent and Ongoing Projects

Thermal Mapping of Satellites and Asteroids

The surface compositions of rocky and icy solar system worlds arise from a combination of intrinsic properties (formation conditions, and endogenic processes such as past volcanism), and exogenic processing by their environments. The thermal properties of surface materials both provide compositional constraints, and determine the response of the materials to solar radiation. Millimeter wavelengths probe the upper few cm of rocky and icy surfaces, and are sensitive to the thermal properties of the upper subsurface beneath the most processed exterior. The Atacama Large Millimeter Array (ALMA) in Chile is a new interferometric millimeter-wavelength observatory that is capable of spatially resolving solar system asteroids and satellites, and hence providing maps of the thermal material properties of their surfaces. I use ALMA to generate such thermal maps of the Galilean satellites and of large main belt asteroids (Fig: residual brightness temperature map of Ganymede at a wavelength of 1.3 mm), in order to understand their subsurface composition and temperature profiles, and investigate the relative roles of exogenic vs. endogenic surface processing.

Galilean Satellite Atmospheres and Aurorae

The galilean satellites exhibit a range of atmospheric compositions, thermochemical histories, and magnetic field properties. These objects therefore present a laboratory for studying universal planetary processes including the creation and loss of tenuous atmospheres and the impact of geological activity and plasma environment on surfaces and atmospheres of objects with and without magnetic fields. The atmospheres of Europa and Ganymede are sourced from sputtering of their icy surfaces, while Io's sulfur-based atmosphere is sourced by direct volcanic outgassing and sublimation of surface frosts. The tenuous atmospheres of these worlds produce subtle signatures; I study these signatures at optical and near-infrared wavelengths by observing these satellites when they are in Jupiter's shadow and the sunlight normally reflected off of their bright surfaces is absent. Using this observing technique, I recently used emission from hot volcanic SO gas on Io observed at high spectral resolution to infer gas reservoirs at two temperatures (de Kleer et al. 2019). Currently, I am using optical-wavelength auroral emissions from Io, Europa, and Ganymede to constrain the atmospheric composition and column density, and to investigate the interactions of these species with the jovian magnetosphere and particle environment (Fig; de Kleer and Brown 2018).

High-Resolution Mapping of Io's Volcanoes

The thermal output of Io's volcanoes reveals the properties of the eruption and magma, giving us a window into Io's interior and near-surface magma reservoirs. When individual volcanic features can be spatially resolved, we may distinguish multiple locations where magma is reaching the surface within a single volcanic complex and/or look for variations in properties across such a feature. Using this information, we can start to piece together characteristics of the magma plumbing system. I am currently working with a team at the Large Binocular Telescope to push the limits of current technology in order to achieve extreme spatial resolution on Io with the AO-assisted Large Binocular Telescope Interferometer (LBTI). In Conrad et al. (2015), we used LBTI to directly resolve a volcanic feature on Io for the first time from the Earth, revealing multiple distinct emission components within the lava lake Loki Patera. More recently, we used an occultation of Io by Europa to reconstruct the temperature distribution within Loki Patera at a spatial resolution of 10 km (Fig; de Kleer et al. 2017). The temperature map reveals evidence for two resurfacing waves traveling in opposite directions around the patera at different rates, indicating compositional differences across this 200-km feature.

Press Releases (2017): UC Berkeley | LBTO

The Volcanism and Tidal Heating of Io

Tidal heating plays a central role in geological activity on bodies all across the Solar System. On Io, tidal heat manifests in a clearly detectable way as large-scale volcanism, presenting a truly unique opportunity to connect interior processes to their surface expressions and unravel the mechanisms of tidal heating. I am currently characterizing the statistical properties of Io's eruptions, which discriminate between models of tidal heating and reveal the depth of tidal heat deposition in Io's interior, through a high-cadence adaptive optics imaging campaign at Keck and Gemini N. The dataset reveals the time-evolution of ~60 individual volcanoes over more than 150 nights since the beginning of 2013 (de Kleer et al. 2014;, de Kleer & de Pater 2016a) and constitutes the highest-cadence database of high-resolution observations of Io's thermal emission to date. The observed spatial pattern of thermal activity is distinct and asymmetric (Fig; de Kleer & de Pater. 2016b), implying strong local geological controls on the locations of Io's eruptions, while the latitudinal distribution of high-power events is suggestive of a deep-mantle magma source.

Press Releases (2016): UC Berkeley | Gemini N | Keck

Powerful Volcanic Eruptions on Io

The mechanisms that drive volcanism on Io are very different from on Earth, giving us the opportunity to investigate how the heat source and thermal history of a body impact its geophysical processes. I am interested in studying Io's most powerful and puzzling volcanoes to probe the composition of Io's interior and the architecture of its sub-surface magma systems. Through time-domain coverage of Io's eruptions and simultaneous multi-telescope datasets, I have characterized some of Io's most energetic eruptions (Fig; de Kleer et al. 2014; de Kleer & de Pater 2017) and studied a unique class of eruptions on Io that are intense but very short-lived (de Kleer & de Pater 2016b).

Press Releases (2014): UC Berkeley | Gemini N | Keck

Ice Giant Atmospheres

The composition, circulation, and aerosol structure of planetary atmospheres inform planet formation and evolution models. I study these properties in the atmospheres of Uranus and Neptune using near-infrared adaptive optics observations from Lick Observatory and the Keck telescope. I have collaborated on the development of radiative transfer code to generate synthetic near-infrared spectra of planetary atmospheres. The synthetic models are fit to data using a Markov chain Monte Carlo (MCMC) sampler to determine the properties and distribution of atmospheric aerosols and molecular absorbers, which inform our understanding of global circulation patterns. By applying this code to observations of Uranus and Neptune with the OSIRIS integral-field spectrometer on the Keck telescope, we reconstruct 3D compositional maps of molecules and aerosols in the atmospheres of these planets. Despite major differences in heat flow and cloud activity between the two ice giants, our analysis indicates broad-scale similarities, including an extended haze layer above a compact condensation cloud (de Kleer et al. 2015; Luszcz-Cook et al. 2016). However, while high-latitude methane depletion on Uranus is broadly consistent with hemisphere-scale circulation cells, a lack of analogous trends on Neptune points to a multi-cell circulation pattern.

The Rings of Uranus

Ring systems are an ubiquitous feature of outer Solar System planets; the wide variety in their structure and particle properties indicates diverse formation scenarios, ages, and evolutionary histories. In de Kleer et al. (2013), I isolated the reflectance spectra of individual ring groupings within the Uranian ring system using the OSIRIS integral-field spectrometer on the Keck telescope and produced the first spectrally-resolved observations of the system, which confirm that Uranus' ring particles are neither dusty like Jupiter's nor pure water ice like Saturn's.