A team of planetary researchers from the United States, Canada and Italy has detected an ice-rich linear feature of bedrock in the tropical region of Saturn’s hazy moon Titan.
A false-color view of Titan, a moon of Saturn surrounded by a thick orange haze. Image credit: NASA / JPL / University of Arizona / University of Idaho.
On Titan, atmospheric methane molecules are continuously broken apart by sunlight. The resulting atmospheric haze settles to the surface and accumulates as organic sediments, rapidly depleting the atmospheric methane. This organic veneer is made up of the material of past atmospheres.
There is no obvious source of methane, except from the evaporation of methane from Titan’s polar lakes. But these lakes contain only one-third of the methane in Titan’s atmosphere and will be exhausted soon by geological time scales.
One theory is that the methane could be supplied by subsurface reservoirs that vent methane into the atmosphere. Prior studies of Titan indicate the presence of a singular region called Sotra, which looks like a cryovolcano.
Professor Caitlin Griffith from the Lunar and Planetary Laboratory at the University of Arizona and co-authors set out to study the composition of Titan’s surface, partly hoping to find subtle small cryovolcano candidates.
The scientists analyzed tens of thousands of spectral images taken of the topmost layer of the surface by Cassini’s Visible and Infrared Mapping Spectrometer, using a method that enabled the detection of weak surface features.
They didn’t find any evidence of small cryovolcanoes, but Sotra was found to be exceptional in that it exhibits the strongest ice features.
Yet the major ice feature they found was completely unexpected. It consists of a linear ice corridor that wraps around 40% of Titan’s circumference.
This map indicates that Titan’s icy corridor (blue color) and craters account for most of Titan’s ice-rich surfaces. It shows the dark dune fields (for example, Fensal and Belet), the local regions of Sotra (S), Hotei Regio (H), Tui Regio (T), and the Huygens landing site (X), and three large craters: Menrva (1), Sinlap (2) and Selk (3). Image credit: Griffith et al, doi: 10.1038/s41550-019-0756-5.
“This icy corridor is puzzling, because it doesn’t correlate with any surface features nor measurements of the subsurface,” Professor Griffith said.
“Given that our study and past work indicate that Titan is currently not volcanically active, the trace of the corridor is likely a vestige of the past.”
“We detect this feature on steep slopes, but not on all slopes. This suggests that the icy corridor is currently eroding, potentially unveiling presence of ice and organic strata.”
The team’s analysis also indicated a diversity of organic material in certain regions.
These surface deposits are of interest because laboratory simulations of Titan’s atmosphere produce biologically interesting compounds such as amino acids.
“Both Titan and Earth followed different evolutionary paths, and both ended up with unique organic-rich atmospheres and surfaces,” Professor Griffth said.
“But it is not clear whether Titan and Earth are common blueprints of the organic-rich of bodies or two among many possible organic-rich worlds.”
The study was published in the journal Nature Astronomy.
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Caitlin A. Griffith et al. A corridor of exposed ice-rich bedrock across Titan’s tropical region. Nature Astronomy, published online April 29, 2019; doi: 10.1038/s41550-019-0756-5
