Supplementary material to “Priorities for Future Research on Planetary Dunes”

Timothy N. Titus, U.S. Geological Survey, Flagstaff, Arizona

Nick Lancaster, Desert Research Institute, Reno, Nevada

Rose Hayward, U.S. Geological Survey, Flagstaff, Arizona

Lori Fenton, NASA Ames Research Center, Moffett Field, California

Mary Rourke, Planetary Science Institute, Tucson, Arizona

Citation:

Titus, T. N., N. Lancaster, R. Hayward, L. Fenton, and M. Rourke (2008), Priorities for Future Research on Planetary Dunes, Eos Trans. AGU, 89(45), 447–448.

[Full Article (pdf)]

Proceedings from the 2008 Planetary Dunes Workshop

Timothy N. Titus, United States Geological Survey Nick Lancaster, Desert Research Institute Rose Hayward, United States Geological Survey Lori Fenton, NASA Ames Research Center Mary Bourke, Planetary Science Institute

Landforms and deposits, created by the dynamic interactions between granular material and airflow (aeolian processes), occur on several planetary bodies, including Earth, Mars, Titan, and Venus. The recognition of landforms on other planetary bodies requires use of terrestrial analogs as well as a well-established methodology for interpreting orbital and lander images of landforms on other planetary bodies. If it is assumed that morphologically similar landforms are created in essentially the same manner on different planetary surfaces and that the fundamentals of the landforms and processes are well-understood on Earth [Greeley and Iversen, 1985], it should be possible to use observations of dunes on other planetary bodies to make inferences about the types of surface processes and environments that occur on those unfamiliar landscapes. Such an approach has been applied most successfully on Mars, where there is a history of terrestrial analog studies of landforms and deposits going back to the recognition of dunes on Mariner 9 images in the early 1970s. Terrestrial analog comparisons have also been used to understand airflow and aeolian processes on Titan and Venus. Ironically, the need to understand the physics of surface processes on other planetary bodies has been the impetus for fundamental studies of such processes on Earth.

In order to address many of the outstanding questions within planetary dune research, a workshop was organized that incorporated oral and poster presentations as well as extended discussion dispersed around a one-day field trip to dunes at White Sands National Monument. This workshop, sponsored by LPI and JPL and organized by the USGS, PSI, DRI, and SETI, was held in Alamogordo, NM, April 28-May 2, 2008, and brought together researchers from diverse backgrounds, ranging from image analysis, to modeling, to terrestrial analog studies. A group of approximately 45 researchers from 8 countries (4 continents) had intensive discussions of problems and issues in an attempt to identify the most promising approaches to understanding these dune systems and to developing a collaborative interdisciplinary research agenda. The workshop outlined the current status of planetary aeolian dune research and identified key areas for future research. The agenda and links to the abstracts can be found at the LPI dune meeting website. Selected papers from the workshop will be published in a special issue of Geomorphology, edited by Mary Bourke, Lori Fenton, and Nick Lancaster.

Despite the three decades of research on martian dunes and other aeolian bedforms, studies of these features have yet to answer many of the basic questions regarding their composition and sediment sources, morphologys, ages and origins, and dynamics under present and past climatic conditions. Recently acquired data from orbiters and rovers, together with innovative approaches using terrestrial analogs and numerical models, are beginning to provide new insights into martian sand dunes. Perhaps the most exciting discovery has been the identification of hydrated sulfates, probably gypsum, in some martian dunes [Langevin et al., 2005]. By combining data from a variety of sources (e.g., image data and topography), we are beginning to understand the source and transport pathways of the north polar sand seas [Phillips et al., 2008], as well as some of the intra-crater dunefields in the southern hemisphere of Mars.

The discovery of linear dunes on Titan is a good example of the application of terrestrial analogs to identify landforms in an unfamiliar environment. The linear dunes on Titan are very similar in geometry (width, crest-to-crest spacing, and length) to linear dunes in Namibia and the Rub al Khali of Arabia and show patterns and interactions with pre-existing topography that have direct parallels in terrestrial desert regions [Lorenz et al., 2006]. Dune pattern analysis, in combination with knowledge of wind regimes of linear dune areas on Earth, can be used to constrain formative wind conditions, such that comparisons can be made with models of atmospheric circulation on Titan.

Even on Earth, where extensive field studies are possible, much remains to be done. Many dune areas are remote and inaccessible, requiring use of remote sensing data to determine patterns of morphology and sediment composition. Newly developed techniques of image data analysis allow use of mosaicked thermal IR data (e.g., ASTER) to determine dune composition and sand transport pathways [Scheidt et al., 2008]. Much improved digital topographic data (including lidar) can be used to understand dune morphometry and dynamics, as well as the development of dune patterns over time. New techniques, such as ground penetrating radar, enable understanding of long-term dune development. Process studies of dunes have stalled because the community has realized that existing instrumentation is inadequate to measure key processes, but new developments indicate that great progress will be made in the near future. Numerical modeling of dunes and dune patterns is a dynamic emerging field of study [Elbelrhiti et al., 2008], with great promise for understanding fundamental processes of dune and dune field formation on all planetary bodies [Claudin and Andreotti, 2006]. Comparative studies between dune fields are, however, hampered by the lack of a consistent terminology for dune types and by the lack of a database of dune field occurrence, morphology, and relation to wind regimes.

Based on extensive discussion, the group identified the following top 10 priorities for future planetary dune research:

  1. Facilitate better communication between scientists studying dunes on ALL planetary surfaces through joint research, future workshops, and special sessions at meetings.
  2. More studies of terrestrial analogs are needed to better understand fundamental processes.
    • Field analog studies of BOTH morphology and processes are suggested — especially in relation to interactions between dunes, as dune patterns, as well as interactions between dunes and topography.
    • Because Mars is a cold desert, terrestrial field study sites should include both cold deserts (e.g., Antarctic Dry Valleys for studies of megaripples as analogs for transverse aeolian bedforms (TAR's) on Mars).
    • The potential importance of Pleistocene para- and peri-glacial landscapes is important, given the temperature regime of Mars and the widespread occurrence of frozen ground phenomena. Cold climate physical weathering should be investigated as a source of particles for transport by wind.
  3. Fundamental differences in atmospheric properties (especially density) between planetary bodies have an important effect on boundary layer characteristics and therefore sand transport processes. Such effects have the potential to affect the spatial and temporal scaling of dunes and sediment transport between the Earth, Mars, and Titan. Such issues can be best addressed via a combination of laboratory experiments and numerical modeling.
  4. The relations between dune orientations and winds are known in general terms, but information on specific dune fields is often lacking. Even on Earth, wind data is usually available only for areas marginal to the dune fields. We advocate increased use of small-scale high-resolution climate models (e.g., mesoscale models) in order to develop information on regional and local scale wind fields for comparison with observed wind directions and dune orientations.
  5. Development, completion and/or expansion of planetary dune databases is required.
  6. Additional research is needed to develop or refine dune classification schemes to consider both morphology and formation processes (e.g., effects of wind regimes on dune morphology).
  7. Linear dunes are the most widespread dune type on Earth, but are rare on Mars. They have also recently been identified on Titan. More research on the formation process of linear dunes is needed, especially in relation to linear dunes formed in the lee of topographic obstacles.
  8. More research is required to constrain physical properties (e.g., grain size, degree of induration and cementation) and composition of dune sediments on Mars, Titan, and Earth and how these properties affect remote sensing signatures in VNIR, thermal, and microwave wavelength regions.
  9. Modeling of dune morphodynamics, especially dune initiation and development of dune patterns through merging and linking has progressed rapidly in recent years. Additional numerical and analog (e.g., flume) studies are a priority for understanding observed dune patterns.
  10. Quantification of atmospheric parameters important to aeolian processes (e.g., wind speed and direction, wind shear stress) is necessary for understanding fundamental aspects of sediment transport on planetary surfaces, yet such data are rarely acquired by landers and rovers. Inclusion of such instruments on future planetary missions is needed to advance understanding of the dynamics of wind transport of sediment on planetary surfaces.

A follow-on meeting to assess progress on studies identified by workshop participates is planned for the spring of 2010 at the Great Sand Dunes National Monument, Colorado. For additional information about the workshop, contact the authors, or see www.mars-dunes.org.

References

Claudin, P., and B. Andreotti (2006), A scaling law for aeolian dunes on Mars, Venus, Earth, and for subaqueous ripples, Earth and Planetary Science Letters, 252(1-2), 30-44.

Elbelrhiti, H., et al. (2008), Barchan dune corridors: Field characterization and investigation of control parameters, Journal of Geophysical Research, Earth Surface, 113, F02S15, doi:10.1029/2007JF000767.

Greeley, R., and J. D. Iversen (1985), Wind as a Geological Process, 333 pp., Cambridge University Press, Cambridge.

Langevin, Y., F. Poulet, J-P. Bibring, B. Gondet (2005), Sulfates in the North Polar Region of Mars Detected by OMEGA/Mars Express, Science, 307, 1584–1586.

Lorenz, R. D., et al. (2006), The sand seas of Titan: Cassini RADAR observations of longitudinal dunes, Science, 312, 724–727.

Phillips, R. J., et al. (2008), Mars North Polar Deposits: Stratigraphy, Age, and Geodynamical Response, Science, 320(5880), 1182–1185.

Scheidt, S., et al. (2008), Radiometric normalization and image mosaic generation of ASTER thermal infrared data: An application to extensive sand sheets and dune fields, Remote Sensing of Environment, 112(3), 920–933.