FIRST MEASUREMENTS OF RIPPLE HEIGHTS ON MARS

Aeolian processes are likely the most active geologic processes occurring on Mars today. Dust storms and dust devils have been observed in recent years, and dunes and ripple-like forms have been observed in many areas. Although it is not known whether or not dunes and ripples are still active, these aeolian forms provide information about the past (if not present) wind regime on Mars.

Mars Orbiter Camera (MOC) images from Mars Global Surveyor have provided a view of dunes and ripples that was not previously available. Several authors have used MOC images to discuss the stratigraphic relationships between dunes and ripples and to compare their albedos. Shape measurements of terrestrial ripples have been used in comparisons to martian ripple forms in an attempt to determine exactly what type of aeolian bedform is represented by the ripple forms on Mars.

It is possible to measure the crest spacing of ripple forms from MOC images, but heights of ripples have not been measured to date. The heights of martian dunes have only recently been measured using MOLA topographic data and stereo measurements. Smaller barchan dunes are ~30 m in height whereas larger dunes can be ~100 m. As more MOC images are released, stereo pairs with sufficient resolution and angular separation become available for attempts at stereo measurements of ripple heights.

Here we report on results from the first height measurements of ripple forms on Mars. Although available image resolutions prevent measurement of smaller forms, ripples with crest spacing of ~38 m were measured to have heights of ~5.7 m. This gives a ripple wavelength to height ratio of ~6.7, whereas that ratio is ~15 for terrestrial ripples. If this ratio remains consistent for other areas on Mars, it would suggest that martian ripples are twice as tall as their terrestrial counterparts for a given ripple wavelength. The greater heights of martian ripples may be the result of the lower martian gravity and other factors.