Shifting sands of Titan *IMAGES*
Embargoed until:
08-Dec-2014 11:00 US Eastern time | 16:00 London time
09-Dec-2014 01:00 Japanese time | 03:00 Australian Eastern time
DOI: 10.1038/nature14088
DOI: 10.1038/ngeo2323
Dune formation on Titan, Saturn’s largest moon, requires higher wind speeds than
expected and the dunes evolve over timescales that are much longer than previously
thought. These findings, presented in two independent studies published
in Nature and Nature Geoscience this week, offer new insights into the processes that
shape sand dunes, which may provide clues about dune formation on other planets
and moons.
The wind-blown dune formations on Titan are thought to be similar to those found on
Earth, Mars and Venus. Modelling studies have been performed to determine the
conditions that produce dunes on Titan, but it is unclear how accurate these models
are. Wind tunnel experiments designed to simulate surface conditions on Titan,
reported by Devon Burr and colleagues in Nature, indicate that threshold wind speeds
required to move sand for dune formation are around 40 per cent higher than
predicted by current models. These results lend support to the idea that only rare
strong westerly winds control dune movement, rather than the easterly winds that are
thought to be most common on Titan.
A second study by Ryan Ewing and colleagues, detailed in Nature Geoscience,
analyses images of Titan’s dunes taken by NASA’s Cassini spacecraft. The results
imply that long-term climate cycles associated with variations in Saturn’s orbit control
the sand-dune patterns on Titan. The authors estimate that the observed
reorientation of some dune crests would have taken around 3,000 Saturn years
(around 88,000 Earth years) or longer. This timescale exceeds that of diurnal,
seasonal, or tidal wind cycles, which have previously been suggested to be drivers of
these patterns, and suggests that Titan’s dunes — like large dune fields on Earth —
are shaped by long-term climate cycles.
CONTACT
Devon Burr (University of Tennessee-Knoxville, TN, USA)
Tel: +1 865 974 6010; E-mail: dburr1@utk.edu
Ryan Ewing (Texas A&M University, College Station, TX, USA)
Tel: +1 512 917 4267; E-mail: rce@geos.tamu.edu
Please link to the scientific paper in online versions of your report (the URL will go live
after the embargo ends):
http://dx.doi.org/10.1038/nature14088
http://dx.doi.org/10.1038/ngeo2323
Image 1 Caption: Degraded sand dune patterns seen in this radar image taken by
the Cassini spacecraft show evidence of shifting winds on Titan.
Credit: Cornell/Laboratoire AIM Paris-Diderot
Image 2 Caption: Degraded sand dune patterns seen in this radar image taken by
the Cassini spacecraft show evidence of shifting winds on Titan.
Credit: Cornell/Laboratoire AIM Paris-Diderot