Aaru Is Equatorial Dark Albedo Feature on Titan's Saturn-Facing Side

Summary: Aaru is an equatorial dark albedo feature on Titan's Saturn-facing side that forms a low albedo equatorial quartet with Fensal, Aztlan and Senkyo.

image of dark albedo quartet of (upper left to lower right) Fenzal, Aztlan, Aaru and Senkyo, obtained June 9, 2009, by Cassini spacecraft's Narrow-Angle Camera (NAC), using a spectral filter with sensitivity to 938 nanometer-centered near-infrared light wavelengths; image obtained at an approximate distance of 1.2 million kilometers (746,000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 26 degrees; image addition date 2009-8-18; image credit NASA/JPL/Space Science Institute: May be used for any purpose without prior permission, via NASA JPL Photojournal

Aaru is an equatorial dark albedo feature on Titan's Saturn-facing side that forms an equatorial quartet of low albedo, or low reflectance, with the three optically dark neighboring regions of Fensal, Aztlan and Senkyo.

Aaru is centered at 10 degrees north latitude, 340 degrees west longitude, according to the International Astronomical Union’s (IAU) Gazetteer of Planetary Nomenclature. The Gazetteer gives the optically dark albedo feature's center latitude of 10 degrees north as its northernmost and southernmost latitudes and its center longitude of 340 degrees west as its easternmost and westernmost longitudes as well.

The IAU has assigned a planetographic coordinate system to Titan, according to the Gazetter's page on "Coordinate Systems for Planets and Satellites." Titan's assigned planetographic latitude system of positive longitudinal direction westward facilitates mapping the prograde, west-to-east rotator, explains Bryan Stiles, Cassini RADAR ground processing engineer, in Cassini Radar Basic Image Data Records SIS (Software Interface Specification) (page 7; Appendix B), published Sep. 27, 2005, by NASA's Jet Propulsion Laboratory.

Aaru's centered location in the far western longitudinal reaches of the Titanean equatorial belt's low northern latitude places the optically dark feature in proximity to a trio of similarly darkened albedo features. Aaru Regio forms a dark quartet of low reflectance with northern equatorial-centered Aztlan and southern equatorial-centered Fensal and Senkyo.

Dark Senkyo's center lies to the southeast of Aaru Regio in Titan's southern equatorial belt. The low reflector is centered at minus 5 degrees south latitude, 320 degrees west longitude. The dark albedo feature's center latitude and longitude are repeated as its northernmost-southernmost latitudes and its easternmost-westernmost longitudes, respectively.

Fensal's center is located to the southeast of Aaru in Titan's northern equatorial belt. The dark albedo feature is centered at 5 degrees north latitude, 30 degrees west longitude. The low reflector's center latitude and longitude are given as its northernmost-southernmost latitudes and easternmost-westernmost longitudes, respectively.

Aztlan's center is sited to the southeast of Aaru in Titan's southern equatorial belt. The dark albedo feature is centered at minus 10 degrees south latitude, 20 degrees west longitude. The low reflector's center latitude and longitude are repeated as its northernmost-southernmost latitudes and easternmost-westernmost longitudes, respectively.

Planetary geologist Jeremy Florian Brossier and 12 co-authors discuss infrared (IR) observations of Aaru in their research article, "Geological Evolution of Titan's Equatorial Regions: Possible Nature and Origin of the Dune Material," published in the May 2018 issue of the Journal of Geophysical Research: Planets (pages 1094-1095). The Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft obtained the observations during two flybys of Aaru Regio. The first VIMS flyby, T61, took place August 2009. The second VIMS flyby, T109, occurred in February 2015. The authors noted the collection of Synthetic Aperture Radar (SAR) and High Altitude SAR (HiSAR) swaths, for morphological property retrieval of the terrains, during three flybys (T23 in January 2007; T104 in August 2014; T108 in January 2015).

The authors confine Aaru Regio's latitudinal expanse from 5 degrees south to 15 degrees north and longitudinal stretch from 330 degrees west to 360 degrees west. The large region presents a mixture of low and intermediate albedo units.

The feature's SAR swaths reveal northwestern Aaru as surrounded by locally bright IR-bright units that imply rough surfaces at the RADAR wavelength, as exemplified by the mountainous-like terrain of Handir Colles. Handir Colles is centered at 10 degrees north latitude, 356.68 degrees west longitude. Northernmost and southernmost latitudes reach 10.87 degrees north and 9.23 degrees north, respectively. It records easternmost and westernmost longitudes of 355.35 degrees west and 357.65 degrees west, respectively. Handir Colles has a diameter of 100 kilometers.

Lying to the south of Handir Colles, Giedi Planitia yields IR-blue and SAR-intermediate observations that suggest a duneless landform. Giedi Planitia is centered at 5.22 degrees north latitude, 357.02 degrees west longitude. The plain's northernmost and southernmost latitudes occur at 7.92 degrees north and 3.04 degrees north, respectively. It establishes easternmost and westernmost longitudes of 353.74 degrees west and 360.51 degrees west, respectively. Giedi Planitia's diameter measures 303.26 kilometers.

Perched in the southeast, between Aaru and Senkyo, Paxsi projects IR- and SAR-brightened rims and south-offset central peak as well as IR-brown and SAR-dark duney infill of the interior floor. The large-ringed feature is centered at 5 degrees north latitude, 341.2 degrees west longitude. Its northernmost and southernmost latitudes stretch from 6.7 degrees north to 3.7 degrees north, respectively. Paxsi sets its easternmost and westernmost longitudes at 339.8 degrees west and 342.6 degrees west, respectively. The large-ringed feature's diameter spans 120 kilometers.

The Gazetteer of Planetary Nomenclature's "Categories (Themes) for Naming Features on Planets and Satellites" page explains the IAU convention for naming Titan's albedo features as drawing upon "Sacred or enchanted places, paradise, or celestial realms from legends, myths, stories, and poems of cultures from around the world." In 2006, Aaru received IAU approval for its name, which references the ancient Egyptian "abode of the blessed dead."

Dark quartet of Fensal and Aztlan (left) and Aaru and Senkyo (right) appear close to center of Titan VIMS (Visual and Infrared Mapping Spectrometer) image; map shows only prominent albedo features and a few other easily-distinguishable features; map coverage between 90 degrees north and 90 degrees south; map credit NASA/JPL/University of Arizona: No known copyright restrictions, via IAU-USGS Astrogeology Science Center's Gazetteer of Planetary Nomenclature

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Dedication

This post is dedicated to the memory of our beloved blue-eyed brother, Charles, who guided the creation of the Met Opera and Astronomy posts on Earth and Space News. We memorialized our brother in "Our Beloved Blue-Eyed Brother, Charles, With Whom We Are Well Pleased," published on Earth and Space News on Thursday, Nov. 18, 2021, an anniversary of our beloved father's death.

Image credits:

image of dark albedo quartet of (upper left to lower right) Fenzal, Aztlan, Aaru and Senkyo, obtained June 9, 2009, by Cassini spacecraft's Narrow-Angle Camera (NAC), using a spectral filter with sensitivity to 938 nanometer-centered near-infrared light wavelengths; image obtained at an approximate distance of 1.2 million kilometers (746,000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 26 degrees; image addition date 2009-8-18; image credit NASA/JPL/Space Science Institute: May be used for any purpose without prior permission, via NASA JPL Photojournal @ https://photojournal.jpl.nasa.gov/catalog/PIA11560

Dark quartet of Fensal and Aztlan (left) and Aaru and Senkyo (right) appear close to center of Titan VIMS (Visual and Infrared Mapping Spectrometer) image; map shows only prominent albedo features and a few other easily-distinguishable features; map coverage between 90 degrees north and 90 degrees south; map credit NASA/JPL/University of Arizona: No known copyright restrictions, via IAU-USGS Astrogeology Science Center's Gazetteer of Planetary Nomenclature @ https://planetarynames.wr.usgs.gov/images/titan_VIMS_comp.pdf

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