Michael Malaska

Precipitation-induced surface brightenings seen on Titan by Cassini VIMS and ISS

AbstractObservations from Cassini VIMS and ISS show localized but extensive surface brightenings in the wake of the 2010 September cloudburst. Four separate areas, all at similar latitude, show similar changes: Yalaing Terra, Hetpet Regio, Concordia Regio, and Adiri. Our analysis shows a general pattern to the time-sequence of surface changes: after the cloudburst the areas darken for months, then brighten for a year before reverting to their original spectrum. From the rapid reversion timescale we infer that the process driving the brightening owes to a fine-grained solidified surface layer. The specific chemical composition of such solid layer remains unknown. Evaporative cooling of wetted terrain may play a role in the generation of the layer, or it may result from a physical grain-sorting process.

Spectral properties of Titan's impact craters imply chemical weathering of its surface

Abstract We examined the spectral properties of a selection of Titans impact craters that represent a range of degradation states. The most degraded craters have rims and ejecta blankets with spectral characteristics that suggest that they are more enriched in water ice than the rims and ejecta blankets of the freshest craters on Titan. The progression is consistent with the chemical weathering of Titans surface. We propose an evolutionary sequence such that Titans craters expose an intimate mixture of water ice and organic materials, and chemical weathering by methane rainfall removes the soluble organic materials, leaving the insoluble organics and water ice behind. These observations support the idea that fluvial processes are active in Titans equatorial regions.

Composition, seasonal change, and bathymetry of Ligeia Mare, Titan, derived from its microwave thermal emission

For the last decade, the passive radiometer incorporated in the Cassini RADAR has recorded the 2.2 cm wavelength thermal emission from Titans seas. In this paper, we analyze the radiometry observations collected from February 2007 to January 2015 over one of these seas, Ligeia Mare, with the goal of providing constraints on its composition, bathymetry, and dynamics. In light of the depth profile obtained by Mastrogiuseppe et al. (2014) and of a two-layer model, we find that the dielectric constant of the sea liquid is <1.8, and its loss tangent is inline image. Both results point to a composition dominated by liquid methane rather than ethane. A high methane concentration suggests that Ligeia Mare is primarily fed by methane-rich precipitation and/or ethane has been removed from it (e.g., by crustal interaction). Our result on the dielectric constant of the seafloor is less constraining inline image, but we favor a scenario where the floor of Ligeia Mare is covered by a sludge of compacted and possibly nitrile-rich organic material formed by the deposition of photochemical haze or by rain washing of the nearby shores. We use these results to produce a low-resolution bathymetry map of the sea. We also estimate the temperature variation of the bulk sea between February 2007 and July 2013 to be <2 K, which provides a constraint on its net evaporative cooling currently being explored in ocean circulation models. Lastly, we suggest a lag in the summer warming of the northern polar terrains.

Topographic Constraints on the Evolution and Connectivity of Titan's Lacustrine Basins

The topography provided by altimetry, SAR-Topo, and stereo radargrammetry has opened new doors for Titan research by allowing for quantitative analysis of morphologic form. Using altimetry measurements, we show that Titans Maria are consistent with an equipotential surface but that several filled lakes are found to be hundreds of meters above this sea level, suggesting that they exist in isolated or perched basins. Within a given drainage basin, empty lake floors are typically higher than the liquid elevation of nearby lakes/seas, suggesting local subsurface connectivity. The majority of Titans lakes reside in topographically-closed, sharp-edged depressions whose planform curvature suggests lateral expansion through uniform scarp retreat. Many, but not all, empty lake basins exhibit flat floors and hectometer-scale raised rims that present a challenge to formation models. We conclude that dissolution erosion can best match the observed constraints, but that challenges remain in the interpretation of formation processes and materials.

Alluvial and fluvial fans on Saturn’s moon Titan reveal processes, materials and regional geology

Abstract Fans, landforms that record the storage and transport of sediment from uplands to depositional basins, are found on Saturns moon Titan, a body of significantly different process rates and material compositions from Earth. Images obtained by the Cassini spacecrafts synthetic aperture radar reveal morphologies, roughness, textural patterns and other properties consistent with fan analogues on Earth also viewed by synthetic aperture radar. The observed fan characteristics on Titan reveal some regions of high relative relief and others with gentle slopes over hundreds of kilometres, exposing topographic variations and influences on fan formation. There is evidence for a range of particle sizes across proximal to distal fan regions, from c. 2 cm or more to fine-grained, which can provide details on sedimentary processes. Some features are best described as alluvial fans, which implies their proximity to high-relief source areas, while others are more likely to be fluvial fans, drawing from larger catchment areas and frequently characterized by more prolonged runoff events. The presence of fans corroborates the vast liquid storage capacity of the atmosphere and the resultant episodic behaviour. Fans join the growing list of landforms on Titan derived from atmospheric and fluvial processes similar to those on Earth, strengthening comparisons between these two planetary bodies.

The Spectral Nature of Titan's Major Geomorphological Units: Constraints on Surface Composition

We investigate Titans low- and mid-latitude surface using spectro-imaging near-infrared data from Cassini/VIMS. We use a radiative transfer code to first evaluate atmospheric contributions and then extract the haze and the surface albedo values of major geomorphological units identified in Cassini Synthetic Aperture Radar data, which exhibit quite similar spectral response to the VIMS data. We have identified three main categories of albedo values and spectral shapes, indicating significant differences in the composition among the various areas. We compare with linear mixtures of three components (water ice, tholin-like, and a dark material) at different grain sizes. Due to the limited spectral information available, we use a simplified model, with which we find that each albedo category of regions of interest can be approximately fitted with simulations composed essentially by one of the three surface candidates. Our fits of the data are overall successful, except in some cases at 0.94, 2.03, and 2.79 μm, indicative of the limitations of our simplistic compositional model and the need for additional components to reproduce Titans complex surface. Our results show a latitudinal dependence of Titans surface composition, with water ice being the major constituent at latitudes beyond 30°N and 30°S, while Titans equatorial region appears to be dominated partly by a tholin-like or by a very dark unknown material. The albedo differences and similarities among the various geomorphological units give insights on the geological processes affecting Titans surface and, by implication, its interior. We discuss our results in terms of origin and evolution theories.

Experimental determination of the kinetics of formation of the benzene-ethane co-crystal and implications for Titan

Benzene is found on Titan and is a likely constituent of the putative evaporite deposits formed around the hydrocarbon lakes. We have recently demonstrated the formation of a benzene-ethane co-crystal under Titan-like surface conditions. Here we investigate the kinetics of formation of this new structure as a function of temperature. We show that the formation process would reach completion under Titan surface conditions in ~18 h and that benzene precipitates from liquid ethane as the co-crystal. This suggests that benzene-rich evaporite basins around ethane/methane lakes and seas may not contain pure crystalline benzene, but instead benzene-ethane co-crystals. This co-crystalline form of benzene with ethane represents a new class of materials for Titans surface, analogous to hydrated minerals on Earth. This new structure may also influence evaporite characteristics such as particle size, dissolution rate, and infrared spectral properties.

Prospects for mineralogy on Titan

Abstract Saturn’s moon Titan has a surface that is dominated by molecular materials, much of which are photochemically produced in the moon’s atmosphere. This outlook reviews the potential minerals that would be expected to form on the surface and subsurface of Titan from these molecular solids. We seek to classify them and look toward how the future study of these minerals will enhance our understanding of this planetary body. The classification uses the basis of intermolecular interactions, with the materials grouped into “Molecular solids,” “Molecular co-crystals,” and “Hydrates” classes alongside speculation on other possible classes of potential Titan minerals.

Development of a Deep Drill System with Integrated Deep UV/Raman Spectrometer for Mars and Europa

SPECTROMETER FOR MARS. Joey Palmowski, Boleslaw Mellerowicz, Evan Eshelman, Kris Zacny, Gale Paulsen, Michael Malaska, John C Priscu, William Abbey, Ivria Doloboff, Arthur L Lane, Luther W Beegle, Lauren P DeFlores, Brandi L Carrier, Peter Ngo, Paul Chow, Robert Huddleston, Albert Ridilla, Alexander Wang, Jameil Bailey, Huey Nguyen, Rohit Bhartia Honeybee Robotics, Altadena, CA, United States, NASA Jet Propulsion Laboratory, Pasadena, CA, United States, Montana State University, Land Resources and Environmental Science, Bozeman, MT, United States

Design of a low cost mission to the Neptunian system

Visited only by Voyager 2 in 1989, Neptune and its moon Triton hold important clues to the formation and evolution of the solar system and exoplanetary systems. Neptune-sized planets are the most commonly discovered exoplanets to date. Neptune, an ice giant, is theorized to have migrated from its formation location in the early solar system. This migration affects the expected interior structure, composition, and dynamical evolution of the planet. Triton is conjectured to be a heavily-processed, captured Kuiper Belt Object (KBO), a remnant from the early solar nebula and unique in our solar system. Triton may possess a subsurface aqueous ocean, making it an important astrobiological target. The 2013-2022 Planetary Science Decadal Survey [1] identified a number of high priority science goals for the Neptunian system, including understanding the structure, composition, and dynamics of Neptunes atmosphere and magnetosphere, as well as surveying the surface of Triton. Following these guidelines, we present a low cost flyby mission concept to Neptune and Triton: TRIDENT (Taking Remote and In-situ Data to Explore Neptune and Triton). TRIDENT would carry six instruments and a government furnished atmospheric probe and would provide significant improvements over the scientific measurements undertaken by Voyager 2. In this paper, we first provide a detailed overview of the science questions pertaining to Neptune and Triton and of the science investigations necessary to elucidate them. We then present the design of TRIDENTs instrument suite, the trajectory and the spacecraft, as well as the motivation behind each of our choices. In particular, we demonstrate that, for a mission launched on an Atlas V 551, a Neptune orbiter mission would be infeasible with current technology levels without the use of aerocapture. We therefore present a flyby mission concept with a cost lower than FY2015