James Tuttle Keane
LUNAR TRUE POLAR WANDER, RECORED IN ICE
The Moon hides water ice in permanently shadowed regions near its north and south poles. Curiously, that ice isn't centered at either pole; instead it is clustered in two regions slightly off either pole, but antipodal to one another. We hypothesize that this asymmetric distribution is the really a volatile paleopole, recording a previous lunar spin axis.
Using a combination of geophysical data, and analytic and numerical methods, I showed that this reorientation was likely due to the formation and evolution of the Procellarum KREEP terrain (PKT) on the lunar nearside. (The PKT is what gives the Moon its "face.") This is a critical discovery because it provides a new geophysical tie-point between the Moon's geologic history, rotational motion, and history of volatile stability.
Publications: Siegler et al 2016, Keane et al. in prep.
REORIENTATION AND FAULTING OF PLUTO
New Horizons revealed Pluto to be an astonishingly dynamic world. The most prominent feature on its surface is Sputnik Planitia, a gigantic glacier of actively convecting nitrogen ice.
Through a combination of theoretical modeling and geologic mapping, I showed that Sputnik Planitia is integral to the geologic evolution of Pluto. The thick glacier both controls the orientation of Pluto, and generates significant stresses in Pluto's crust—which are responsible for the global network of extensional faults criss-crossing Pluto's surface. This is likely symptomatic of a feedback between volatile transport, climate, and rotational dynamics. These feedbacks may be active on other icy worlds.
Publications: Keane et al. 2016, White et al. 2018, Cruikshank et al. 2019a, b.
THE SPATIAL-DISTRIBUTION OF IO'S VOLCANOES
Jupiter's moon Io is the most tidally deformed and heated world in the solar system—as evidenced by the hundreds of continually erupting volcanoes dotting its surface. This same tidal heating is enables the formation of subsurface oceans within other icy satellites, like Europa and Enceladus.
While Io is the prototype body for tidal heating, we still don't truly understand how or where tidal heat is deposited within Io, and how that heat translates into the activity we see at the surface. To help address this, I am employing a new, comprehensive spherical harmonic analysis of the spatial distribution of volcanoes, mountains, tectonics, and other features on Io. The goal is to identify patterns that could inform models of tidal heating.
Publications: Keane et al., in prep.
TUMBLING WORLDS IN THE AFTERMATH OF LARGE IMPACTS
Asteroid and comet impacts can have dramatic consequences for the spins of planets and planetary satellites. Impacts can stir-up and perturb the core dynamo, generate stresses in the crust, and alter the stability of volatiles on the surface. Although many previous studies have investigated the dynamical consequences of impacts, most use over-simplified analytic models that do not accurately reflect the impact process.
I have been working to couple impact hydrocode (iSALE) simulations, gravity measurements, and the analytical and numerical formalisms of rotational dynamics, in order to develop a wholistic model for how impact processes effect the rotation of planets and planetary satellites.
My analysis indicates that previous studies have significantly underestimated the effects of impacts on planetary rotation. For lunar impact basins, I find that smaller impacts can trigger periods of non-principal axis rotation, and in some cases, unlock the Moon from synchronous rotation. This has important consequences for the long-term stability of the Moon's polar volatiles.
Publications: Keane et al. in prep.