Planetary Science

Whence the Streaks?

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Science  15 Oct 2010:
Vol. 330, Issue 6002, pp. 296
DOI: 10.1126/science.330.6002.296-b
CREDIT: MUSHKIN ET AL., GEOPHYS. RES. LETT. 10.1029/2010GL044535 (2010)

One of the signs of ongoing geologic activity on Mars is the formation of dark streaks on slopes in the equatorial regions. Thousands of such streaks have been seen; they appear over periods as short as a few months in repeated satellite observations. Several possible origins have been proposed. Mushkin et al. combined spectral data and high-resolution images of several streaks on Olympus Mons to constrain the options. Identification of specific outcrops and boulder bounces down the slope ruled out selective exposure of substrate as an origin. The spectral data indicate that the streaks are rich in iron oxides but also suggest that water is not currently present (they are not wet now). One possible hypothesis to reconcile these data would entail transient seepage of a brine layer during the warmer Martian summer out along a thin surface layer protected by dust, causing precipitation of iron oxides and silica before the water completely evaporates or sublimes.

Geophys. Res. Lett. 10.1029/2010GL044535 (2010).

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