A Common Origin for Ridge-and-Trough Terrain on Icy Satellites by Sluggish Lid Convection

Ridge-and-trough terrain is a common landform on outer Solar System icy satellites. Examples include Ganymede's grooved terrain, Europa's gray bands, Miranda's coronae, and several terrains on Enceladus. The conditions associated with the formation of each of these terrains are similar: heat flows of order tens to a hundred milliwatts per meter squared, and deformation rates of order $10^{-16}$ to $10^{-12}$ s$^{-1}$. Our prior work shows that the conditions associated with the formation of these terrains on Ganymede and the south pole of Enceladus are consistent with vigorous solid-state ice convection in a shell with a weak surface. We show that sluggish lid convection, an intermediate regime between the isoviscous and stagnant lid regimes, can create the heat flow and deformation rates appropriate for ridge and trough formation on a number of satellites, regardless of the ice shell thickness. For convection to deform their surfaces, the ice shells must have yield stresses similar in magnitude to the daily tidal stresses. Tidal and convective stresses deform the surface, and the spatial pattern of tidal cracking controls the locations of ridge-and-trough terrain.Comment: 45 pages, 7 figures; accepted for publication in Physics of the Earth and Planetary Interior

Interior Structures and Tidal Heating in the TRAPPIST-1 Planets

With seven planets, the TRAPPIST-1 system has the largest number of exoplanets discovered in a single system so far. The system is of astrobiological interest, because three of its planets orbit in the habitable zone of the ultracool M dwarf. Assuming the planets are composed of non-compressible iron, rock, and H$_2$O, we determine possible interior structures for each planet. To determine how much tidal heat may be dissipated within each planet, we construct a tidal heat generation model using a single uniform viscosity and rigidity for each planet based on the planet's composition. With the exception of TRAPPIST-1c, all seven of the planets have densities low enough to indicate the presence of significant H$_2$O in some form. Planets b and c experience enough heating from planetary tides to maintain magma oceans in their rock mantles; planet c may have eruptions of silicate magma on its surface, which may be detectable with next-generation instrumentation. Tidal heat fluxes on planets d, e, and f are lower, but are still twenty times higher than Earth's mean heat flow. Planets d and e are the most likely to be habitable. Planet d avoids the runaway greenhouse state if its albedo is $\gtrsim$ 0.3. Determining the planet's masses within $\sim0.1$ to 0.5 Earth masses would confirm or rule out the presence of H$_2$O and/or iron in each planet, and permit detailed models of heat production and transport in each planet. Understanding the geodynamics of ice-rich planets f, g, and h requires more sophisticated modeling that can self-consistently balance heat production and transport in both rock and ice layers.Comment: 34 pages, 3 tables, 4 figures. Accepted for publication in Astronomy & Astrophysics -- final version including corrections made in proof stag

Interpreting the densities of the Kuiper belt's dwarf planets

Kuiper Belt objects with absolute magnitude less than 3 (radius $\gtrsim$500 km), the dwarf planets, have a range of different ice/rock ratios, and are more rock-rich than their smaller counterparts. Many of these objects have moons, which suggests that collisions may have played a role in modifying their compositions. We show that the dwarf planets fall into two categories when analysed by their mean densities and satellite-to-primary size ratio. Systems with large moons, such as Pluto/Charon and Orcus/Vanth, can form in low-velocity grazing collisions in which both bodies retain their compositions. We propose that these systems retain a primordial composition, with a density of about 1.8 g/cm$^3$. Triton, thought to be a captured KBO, could have lost enough ice during its early orbital evolution to explain its rock-enrichment relative to the primordial material. Systems with small moons, Eris, Haumea, and Quaoar, formed from a different type of collision in which icy material, perhaps a few tens of percent of the total colliding mass, is lost. The fragments would not remain in physical or dynamical proximity to the parent body. The ice loss process has not yet been demonstrated numerically, which could be due to the paucity of KBO origin simulations, or missing physical processes in the impact models. If our hypothesis is correct, we predict that large KBOs with small moons should be denser than the primordial material, and that the mean density of Orcus should be close to the primordial value.Comment: 8 pages, 2 figures. Accepted for publication in MNRA

Applied Solutions for Water Resource Challenges: Floods, Contamination and Upland Water Storage

poster abstractThe Center for Earth and Environmental Science, an IUPUI Signature Center, is working on a series of water resources problems and creating solutions. A series of collaborative projects are underway with the HUD, FEMA, the Office of Community and Rural Affairs, the United States Geological Survey, the Indiana State Department of Agriculture, and an international corporate partner in Berlin, KompetenzZentrum Wasser Berlin. Flood Erosion Hazard Program CEES, the USGS, and Polis are working with HUD and the Office of Community and Rural Affairs, though the Indiana Silver Jackets, to create tools for the State of Indiana to incorporate flood erosion hazard risk assessments into community planning. Flooding remains the most costly natural hazard in the US and Indiana. Flood losses continue to rise despite billions of dollars in mitigation. The causes are complex and related to land use, infrastructure design and climate change. Following the June 2008 floods in Indiana, 39 counties were listed as Federal disaster areas. In early 2005, 90% of Indiana counties were declared federal disaster areas after heavy rains fell on saturated soil. There have been seven major regional flooding events since the “Great flood of 1913”. The frequency of large floods appears to be increasing. Four of the eight major floods have occurred since 1982 and the last two occurred in 2005 and 2008. From 1998 through 2007, total insured flood losses in Indiana exceeded $39.8 million. While more restricted in area than the floods of 2008; record flooding occurred again throughout central and southern Indiana in early 2011 following heavy rains in February and March. Traditional flood protection usually consists of three components: flood control reservoirs, urban levees/floodwalls, and agricultural levees. These traditional flood protection methods are focused on one aspect of flooding – inundation. However, the largest single source of flood losses, both in terms of cost and number of affected persons, is damage to transportation infrastructure. Fluvial erosion is a principal cause of this damage. This significant flood-related natural hazard – the “fluvial erosion hazard” (FEH) – is not a specific component of State and local mitigation programs. This project aims to generate the tools for inclusion of FEH into statewide and local community planning. Aquisafe II - Performance Analysis of Selected Mitigation Systems Used to Attenuate Non-Point Source Agricultural Pollution Aquisafe is an international research collaboration with Veolia Environment based in Paris, their corporate partner in Berlin (KompetenzZentrum Wasser – Berlin Center of Competence for Water), the German Federal Environmental Agency, German university partners, and French quasi-governmental agencies in Brittany, France. The project goals are to create new mitigation systems to capture and treat polluted agricultural water running off farm fields prior to flowing into area streams, especially those used for drinking water supplies. The contaminants of specific concern are nutrients (nitrogen and phosphorus) and pesticides (atrazine – a corn-herbicide with potential endocrine disrupting effects). We are testing 2-stage, constructed wetlands in Indianapolis, Indiana and Brittany, France that have been designed to intercept and convert contaminants to harmless compounds. Site designs are guided by laboratory technical scale experiments conducted in Berlin that identified the hydrologic retention times and suitable sources of organic carbon necessary for mitigating contaminants. Construction of the experimental systems will begin in April in the Eagle Creek Watershed in cooperation with a private farmer with initial results expected this summer

Tidal heating and the habitability of the TRAPPIST-1 exoplanets

Context. New estimates of the masses and radii of the seven planets orbiting the ultracool M-dwarf TRAPPIST-1 star permit improved modelling of their compositions, heating by tidal dissipation, and removal of tidal heat by solid-state convection. Aims. Here, we compute the heat flux due to insolation and tidal heating for the inner four planets. Methods. We apply a Maxwell viscoelastic rheology to compute the tidal response of the planets using the volume-weighted average of the viscosities and rigidities of the metal, rock, high-pressure ice and liquid water/ice I layers. Results. We show that TRAPPIST-1d and e can avoid entering a runaway greenhouse state. Planet e is the most likely to support a habitable environment, with Earth-like surface temperatures and possibly liquid water oceans. Planet d also avoids a runaway greenhouse, if its surface reflectance is at least as high as that of the Earth. Planets b and c, closer to the star, have heat fluxes high enough to trigger a runaway greenhouse and support volcanism on the surfaces of their rock layers, rendering them too warm for life. Planets f, g, and h are too far from the star to experience significant tidal heating, and likely have solid ice surfaces with possible subsurface liquid water oceans

The mass and density of the dwarf planet (225088) 2007 OR10

The satellite of (225088) 2007 OR10 was discovered on archival Hubble Space Telescope images and along with new observations with the WFC3 camera in late 2017 we have been able to determine the orbit. The orbit's notable eccentricity, e$\approx$0.3, may be a consequence of an intrinsically eccentric orbit and slow tidal evolution, but may also be caused by the Kozai mechanism. Dynamical considerations also suggest that the moon is small, D$_{eff}$ $<$ 100 km. Based on the newly determined system mass of 1.75x10$^{21}$ kg, 2007 OR10 is the fifth most massive dwarf planet after Eris, Pluto, Haumea and Makemake. The newly determined orbit has also been considered as an additional option in our radiometric analysis, provided that the moon orbits in the equatorial plane of the primary. Assuming a spherical shape for the primary this approach provides a size of 1230$\pm$50 km, with a slight dependence on the satellite orbit orientation and primary rotation rate chosen, and a bulk density of 1.75$\pm$0.07 g cm$^{-3}$ for the primary. A previous size estimate that assumed an equator-on configuration (1535$^{+75}_{-225}$ km) would provide a density of 0.92$^{+0.46}_{-0.14}$ g cm$^{-3}$, unexpectedly low for a 1000 km-sized dwarf planet.Comment: Accepted for publication in Icaru