Linear sand dunes cover the equatorial latitudes of Saturn’s moon Titan and are shaped by global wind patterns1, 2, 3. These dunes are thought to reflect present-day diurnal, tidal and seasonal winds1, 3, 4, 5, 6, but climate models have failed to reproduce observed dune morphologies with these wind patterns4, 6. Dunes diagnostic of a specific wind7, 8 or formative timescale9, 10, 11 have remained elusive3, 5, 12. Here we analyse radar imagery from NASA’s Cassini spacecraft and identify barchan, star and reoriented dunes in sediment-limited regions of Titan’s equatorial dune fields that diverge by 23° on average from the orientation of linear dunes. These morphologies imply shifts in wind direction and sediment availability. Using a numerical model, we estimate that the observed reorientation of dune crests to a change in wind direction would have taken around 3,000 Saturn years (1 Saturn year ∼ 29.4 Earth years) or longer—a timescale that exceeds diurnal, seasonal or tidal cycles. We propose that shifts in winds and sediment availability are the product of long-term climate cycles associated with variations in Saturn’s orbit. Orbitally controlled landscape evolution—also proposed to explain the distribution of Titan’s polar lakes13—implies a dune-forming climate on equatorial Titan that is analogous to Earth.
At a glance
- The sand seas of Titan: Cassini RADAR observations of longitudinal dunes. Science 312, 724–727 (2006). et al.
- Global pattern of Titan’s dunes: Radar survey from the Cassini prime mission. Geophys. Res. Lett. 36, L03202 (2009). &
- Dunes on Titan observed by Cassini Radar. Icarus 194, 690–703 (2008). et al.
- Spectroscopy, morphometry and photoclinometry of Titan’s dune fields from Cassini/VIMS. Icarus 195, 400–414 (2008). et al.
- Multiple origins of linear dunes on Earth and Titan. Nature Geosci. 2, 653–658 (2009). &
- Relevance of fast westerlies at equinox for the eastward elongation of Titan’s dunes. Aeolian Res. 2, 113–127 (2010).
- 1941). The Physics of Blown Sand and Desert Dunes Vol. 265 (Chapman and Hall,
- Bedform alignment in directionally varying flows. Science 237, 276–278 (1987). &
- Flume experiments on the alignment of transverse, oblique, and longitudinal dunes in directionally varying flows. Sedimentology 37, 673–684 (1990). &
- Pattern analysis of dune-field parameters. Earth Surf. Process. Landf. 31, 1176–1191 (2006). , &
- Dune field pattern formation and recent transporting winds in the Olympia Undae Dune Field, north polar region of Mars. J. Geophys. Res. 115, E08005 (2010). , , &
- Implications of dune pattern analysis for Titan’s surface history. Icarus 230, 180–190 (2014). , , &
- An asymmetric distribution of lakes on Titan as a possible consequence of orbital forcing. Nature Geosci. 2, 851–854 (2009). et al.
- 151–168 (SEPM Special Publication 102, 2012). & in Sedimentary Geology of Mars (eds Grotzinger, J. P. & Milliken, R. E.)
- Growth mechanisms and dune orientation on Titan. Geophys. Res. Lett. 41, 6093–6100 (2014). et al.
- Dune formation under bimodal winds. Proc. Natl Acad. Sci. USA 106, 22085–22089 (2009). , , , &
- Reaction, relaxation and lag in natural sedimentary systems: General principles, examples and lessons. Earth-Sci. Rev. 10, 263–342 (1974).
- Insights into Titan’s geology and hydrology based on enhanced image processing of Cassini RADAR data. J. Geophys. Res. 119, 2149–2166 (2014). et al.
- Linear dunes on Titan and Earth: Initial remote sensing comparisons. Geomorphology 121, 122–132 (2010). et al.
- Aeolian dune field self-organization—implications for the formation of simple versus complex dune-field patterns. Geomorphology 72, 94–105 (2005). &
- Linear dunes—forms and formation. Prog. Phys. Geogr. 13, 507–528 (1989).
- Morphology and dynamics of star dunes from numerical modelling. Nature Geosci. 5, 463–467 (2012). , , &
- Aeolian system sediment state: Theory and Mojave Desert Kelso dune field example. Sedimentology 46, 505–515 (1999). &
- Possible tropical lakes on Titan from observations of dark terrain. Nature 486, 237–239 (2012). et al.
- Abrupt onset and termination of the African Humid Period: Rapid climate responses to gradual insolation forcing. Quat. Sci. Rev. 19, 347–361 (2000). et al.
- Bed-form dynamics: Does the tail wag the dog? Geology 25, 771–774 (1997). &
- Late Pleistocene and Holocene dune activity and wind regimes in the western Sahara Desert of Mauritania. Geology 30, 991–994 (2002). et al.
- Fluvial features on Titan: Insights from morphology and modeling. Geol. Soc. Am. Bull. 125, 299–321 (2013). et al.
- Hydrocarbon lakes on Titan: Distribution and interaction with a porous regolith. Geophys. Res. Lett. 35, L09204 (2008). et al.
- Aeolian dune-field pattern boundary conditions. Geomorphology 114, 175–187 (2010). &
- Supplementary Information (4,450 KB)