Extraterrestrial Oceanography of Titan’s Northern Seas from Cassini VIMS Sun Glitter Observations

In this thesis, I investigate the occurrence of sun glitter and waves on the sea surfacesof Titan’s northern seas, Kraken Mare and Punga Mare. These studies of various sun glitter features help to uncover unique liquid bodies, such as liquid-filled channels, better understand the dynamics behind the air-sea-land interactions during the northern summer. Some of these interactions include wind-generated capillary waves, tidal currents, and wave shoaling. In Chapter 1, I introduce the physics of sunglint and sun glitter observations in a terrestrial context and elaborate on the spacecraft geometry that necessitates a sun glitter observation on Titan. In addition, I provide an overview of prior specular observations from the seas on Titan and the geographical context for Titan’s seas. In Chapter 2, I present Cassini VIMS observations of sun glitter – wave-induced reflections from a liquid surface offset from a specular point – on Kraken Mare. Sun glitter reveals rough sea surfaces around Kraken Mare, namely the coasts and narrow straits. The sun glitter observations indicate wave activity driven by the winds and tidal currents in Kraken Mare during northern summer. T104 Cassini VIMS observations show three sun glitter features in Bayta Fretum indicative of variegated wave fields. I cannot uniquely determine one source for the coastal Bayta waves, but I lean toward the interpretation of surface winds, because tidal currents should be too weak to generate capillary-gravity waves in Bayta Fretum. T105 and T110 observations reveal wave fields in the straits of Seldon Fretum, Lulworth Sinus, and Tunu Sinus that likely originate from the constriction of tidal currents. Coastlines of Bermoothes and Hufaidh Insulae adjoin rough sea surfaces, suggesting a complex interplay of windroughened seas and localized tidal currents. Bermoothes and Hufaidh Insulae may share characteristics of either the Torres Strait off Australia or the Åland region of Finland, summarized as an island-dense strait with shallow bathymetry that hosts complex surface circulation patterns. Hufaidh Insulae could host seafloor bedforms formed by tidal currents with an abundant sediment supply, similar to the Torres Strait. The coastlines of Hufaidh and Bermoothes Insulae likely host ria or flooded coastal inlets, suggesting the Insulae may be local peaks of primordial crust isolated by an episode of sea-level rise or tectonic uplift. In Chapter 3, I present new evidence for active coastal and oceanic features in Titan’s Punga Mare observed in a high-phase Cassini VIMS observation of sunglint from the T110 flyby. I observe sunglint in a river, Apanohuaya Flumen, resulting from differing pixel contributions of land adjacent to the channel and implying smooth liquid surfaces. Along the eastern coastline, I identify a 5-m-bright margin. A possible explanation for this brightening may include a coastal margin of rough seas. I find evidence of variegated sea surface roughness in Fundy Sinus and isolated sun glitter near Hawaiki Insulae that suggests seasonal interactions between surface winds and topography. RADAR observations of debouches (where rivers meet bays) within Punga Mare overlap several bright 5 m pixels that indicate rough liquid surfaces. We postulate that a change in liquid flow regimes, possibly occurring as surface streamflow, or bubble outburst events may be responsible for surface roughness near these debouches. These observations imply air-sea-land interactions and hydrological activity are present in Titan’s sea district during the northern summer. In Chapter 4, I summarize the implications of the various sun glitter observations on Titan oceanography.masters, M.S., Physics -- University of Idaho - College of Graduate Studies, 2022-1

Titan’s North–South Haze Asymmetry Ratio and Boundary at Visible Wavelengths over the Cassini Mission

We document the evolution of the north–south asymmetry (NSA) of Titan’s haze albedo during the Cassini mission between 2004 and 2017. We analyze coadded cube images taken at 96 distinct wavelengths between 0.35 and 1.05 μ m by the Cassini Visual and Infrared Mapping Spectrometer (VIMS-V) instrument from 14 Titan flybys. Over half of a Titan year, we observe a near-complete transition in the NSA boundary latitude across the geographic equator from the southern to the northern hemisphere, including a 3 yr fading of the boundary for several years after the equinox. The fading transition of the NSA matches previous observations of a reversal of the NSA in Hubble Space Telescope images of Titan before the winter solstice between 1997 and 2000. A comparison of NSA images taken at similar times but different phase angles shows the NSA boundary is detectable, albeit with less contrast, at moderately high phase angles (∼90°). Analysis of the NSA boundary in T61 and T67 VIMS images further supports a small tilt between the superrotating atmosphere and the solid body of Titan, as suggested in a previous analysis of 0.890 μ m images from the Cassini Imaging Science Subsystem

When and where does it rain on Titan?

We study the temporal and spatial evolution of rain-wetted surface on the north pole of Titan to aid our understanding of seasonality of the methane cycle and its evolution through time. These observations would also enable us to explore the reasons GCM(General Circulation Model) predictions of northern summers differ from the observed rainfall/storm activity. Here, we report wet-sidewalk effect indicating fresh rainfall or near surface fog/cloud activity in at least three other observations of Titan’s North Pole (apart from the first detection made in the T120 flyby [1])

Spatio-temporal Variation of Bright Ephemeral Features on Titan’s North Pole

International audienceAbstract We identify and document the instances of bright ephemeral features (BEF)—bright areas that appear, disappear, and shift from flyby to flyby on Titan’s north pole, using the Cassini Visual and Infrared Mapping Spectrometer data set, thereby developing a sense of their spatial distribution and temporal frequency. We find that BEFs have differing geographic location and spatial extents. However, they have similar observation geometries and orders of surface area coverage and are mostly accompanied by specular reflections. We find the BEFs to represent either broad specular reflection off of a recently wetted surface on the north pole of Titan or a near-surface fog—both owing to probable recent rainfalls. Our surface model constrains the surface roughness to be of 9°–15° indicating the approximate vertical relief of the region to be that of cobbles. We also find that within less than two Titan days the BEF (if on the surface) might infiltrate into the subsurface. We hypothesize the parts of BEFs that extend into the maria to be precipitation fog

New Frontiers Titan Orbiter

International audienceAs one of two planetary objects (other than Earth) that have solid surfaces, thick atmospheres, and astrobiological significance, Titan, like Mars, merits ongoing study with multiple spacecraft. We propose that a Titan orbiter dedicated to geophysics, geology, and atmospheric science be added to the New Frontiers menu for the coming decade