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Astrogeology’s Scientist Helps Solve Martian Riddle

Tim Titus
Timothy Titus

What causes puzzling dark spots, spider-shaped features, and fan-like markings on the icecap at the Martian south pole?

Usually, there are dark spots, typically 50 to 150 feet wide, that are spaced several hundred feet apart and that appear every southern spring as the Sun rises over the icecap. The dark spots last for several months and then vanish, only to reemerge the following year after winter's cold deposits a fresh layer of ice on the cap. Even stranger, the spots seem to reoccur annually in the same locations.

The research of Astrogeology (USGS) Space Scientist, Timothy Titus,(left) in collaboration with Hugh Kieffer (USGS-retiree) and Phil Christensen of ASU research, appears in the August 17, 2006 issue of the scientific journal Nature. Perchance they’ve solved the riddle, although Titus says, “There remain some outstanding questions."

Previous studies suggested that the dark features were areas of early ice defrosting and exposition of dark soil. However the Mars Odyssey Thermal Emission Imaging System (THEMIS) showed that the temperatures of the spots indicated they were far too cold to be bare soil. "We started looking at all of the THEMIS infrared and visual images in the Cryptic region, looking for an area that demonstrated the dynamic nature of the spots," Titus said. "Phil was the one who discovered this area, which we call "Manhattan Island" due to its appearance. We then targeted the THEMIS cameras to take almost daily pictures of the region. The result was a blockbuster movie of one of the most dynamic regions on Mars.

Titus, Kieffer, and Christensen proposed in Nature that the “The seasonal ice cap forms an impermeable, translucent slab of CO2 ice that sublimates from the base, building up high-pressure gas beneath the slab. This gas levitates the ice, which eventually ruptures, producing high-velocity CO2 vents that erupt sand-sized grains in jets to form the spots and erode the channels." These processes are unlike any observed on Earth.

Do read the article in Nature called CO2 jets formed by sublimation beneath translucent slab ice in Mars’ seasonal south polar ice cap.

Tim Titus has also contributed to the following publications:

*Kieffer, H.H., Ttitus, T.Mullins, K & Christensen, P. R. Mars south polar cap behavior observed by TES: Seasonal cap evolution controlled by frost grain size. J.Geophys.Res 105, 9653-9700(2000).

*Christensen, P.R., Kieffer, H.H & Titus, T. Infrared and visible Observations of south polar spots and fans. Eos (Fall Meeting Suppl.)86(52),abstr. P23C-04 (2005)

*Titus, T.N., Kieffer, H.H & Christensen, P.R. Exposed water ice discovered near the south pole of Mars. Science 299, 1048-1051(2003).

*Titus, T.N.,Kieffer, H.H., Mullins,K.F. and Christensen, P. R. TES Pre_mapping data: Slab ice and snow flurries in the Martian north polar night. J.Geophys. Res.106, 23181-23196(2001).

*Kieffer, H.H&Titus, T.N. TES mapping of Mars’ north seasonal cap. Icarus 154,162-189 (2001)

*Haberele, R.M., Mattingly, B&Titus, T.N.Reconciling different observations of CO2 ice mass loading of the martian north polar cap. Geophys.es.Lett.31, LO5702, doi: 10.1029/2004GLO19445(2004).