Active Processes: Bright Streaks and Dark Fans
Active Processes: Bright Streaks and Dark Fans
PSP_002622_0945  Science Theme: Seasonal Processes
In a region of the South Pole known informally as “Ithaca,” numerous fans of dark frost form every spring. HiRISE collected a time lapse series of these images, starting at Ls = 185 and culminating at Ls = 294. Pronounced “el-sub-es” Ls is the way we measure time on Mars: at Ls = 180 the Sun passes the equator on its way south; at Ls = 270 it reaches its maximum subsolar latitude and summer begins.

In the earliest image fans are dark, but small narrow bright streaks can be detected. In the next image, acquired at Ls = 187, just 106 hours later, dramatic differences are apparent. The dark fans are larger and the bright fans are more pronounced and easily detectable. The third image in the sequence shows no bright fans at all.

We believe that the bright streaks are fine frost condensed from the gas exiting the vent. The conditions must be just right for the bright frost to condense.

Written by: Candy Hansen  (12 December 2007)

Acquisition date
16 February 2007

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
246.7 km (153.4 miles)

Original image scale range
49.4 cm/pixel (with 2 x 2 binning) so objects ~148 cm across are resolved

Map projected scale
50 cm/pixel

Map projection

Emission angle

Phase angle

Solar incidence angle
88°, with the Sun about 2° above the horizon

Solar longitude
185.1°, Northern Autumn

For non-map projected images
North azimuth:  121°
Sub-solar azimuth:  34.0°
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Black & white is 5 km across; enhanced color about 1 km
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All of the images produced by HiRISE and accessible on this site are within the public domain: there are no restrictions on their usage by anyone in the public, including news or science organizations. We do ask for a credit line where possible:

NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif., manages the Mars Reconnaissance Orbiter for NASA’s Science Mission Directorate, Washington. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona.