Mimas Temperature Map Shows Unexpected Coldness Around Herschel Crater

Summary: A Mimas temperature map shows unexpected coldness around Herschel Crater, according to data obtained Feb. 13, 2010, by Cassini-Huygens spacecraft.

Upper right image shows unexpected temperature map created from data obtained by the Cassini-Huygens spacecraft’s composite infrared spectrometer (CIRS) on Feb. 13, 2010, the closest-ever flyby of Mimas; lower left image presents Mimas in visible light, with addition of green grid showing latitudes and longitudes at 30-degree intervals; lower right image presents new temperature map on a mosaic of images taken on previous Mimantean flybys; NASA ID PIA12867; image addition date 2010-03-29; image credit NASA / JPL (Jet Propulsion Laboratory) / GSFC (Goddard Space Flight Center) / SwRI (Southwest Research Institute) / SSI (Space Science Institute): May be used for any purpose without prior permission, via NASA JPL Photojournal;

A Mimas temperature map shows unexpected coldness around Herschel Crater, according to data obtained during the Cassini-Huygens spacecraft’s closest-ever flyby Feb. 13, 2010.

The Saturn-exploring Cassini-Huygens spacecraft made its closest-ever Mimantean flyby on Saturday, Feb. 13, 2010. The spacecraft logged an approximate nearness of 9,500 kilometers (5,900 miles) to Mimas.

On that date, as the spacecraft receded from Saturn’s seventh-known moon, its composite infrared spectrometer (CIRS) gathered data on surface temperatures by way of infrared radiation. The National Aeronautics and Space Administration’s (NASA) Goddard Space Flight Center (GSFC) built and manages the Cassini-Huygens spacecraft’s composite infrared spectrometer. The composite infrared spectrometer is “. . . a major science instrument aboard NASA’s Cassini mission to Saturn,” according to the CIRS team’s website. “It measures the infrared energy from Saturn, its rings and its moons, especially Titan, in order to study their thermal structure and composition,” explains the NASA GSFC CIRS website.

The temperature map, published March 29, 2010, on NASA’s Cassini mission pages, distinguishes a colder part (right) of the Mimantean disk from a warmer part (left). A v-shaped boundary clearly separates the two temperature-differentiated parts.

“The warm part has typical temperatures near 92 Kelvin (minus 294 Fahrenheit), while typical temperatures on the cold part are about 77 Kelvin (minus 320 Fahrenheit),” details the multimedia feature’s author, Rebecca Whatmore.

Greater thermal conductivity of the cold part’s surface materials is suspected as the explanation for the cold part’s coldness. The higher rate of conductivity would allow for transfer of solar energy into subsurface materials as opposed to surface warming effectuated by materials with lower thermal conductivity.

Nevertheless, Whatmore notes: “But why conductivity should vary so dramatically across the surface of Mimas is a mystery.”

The cold part of the spectrometer’s Mimantean temperature map includes Hershel Crater. The huge crater, whose diameter approximates one-third of its parent body’s diameter, exhibits warmer temperatures than its environs.

“It’s not yet known whether Herschel is responsible in some way for the larger region of cold temperatures that surrounds it,” Whatmore adds.

Whatmore’s multimedia feature contrasts the spectrometer’s actual temperature map with a map of the expected temperature distribution on Mimas. A white sun symbol indicates the subsolar point, the point at which the sun is perceived as directly overhead, on the map of expected temperatures. The subsolar point occurs close to the equator at midday.

“Just as on Earth, the highest temperatures (shown in yellow) were expected to occur after midday, in the afternoon,” Whatmore explains.

The actual temperature map, however, presents an unexpectedly different pattern from that of the temperature forecast map. Concentric ovals of smoothly varying temperatures radiate from the moon’s equator, with warmer temperatures encompassing equator-straddling latitudes between the subsolar point and, to its east, Herschel Crater.

The spectrometer required 85 minutes for completion of its actual temperature map of Mimas. Data gathering began at a distance of 38,000 kilometers (24,000 miles) and ended at a distance of 67,000 kilometers (42,000 miles) from Mimas.

During data gathering, Mimantean rotation accounted for an increase of the longitude of the center of the moon’s disk from 128 degrees west to 161 degrees west. The moon’s prominent Herschel Crater claims easternmost and westernmost longitudes of 90.91 degrees west and 131.1 degrees west, respectively, according to the International Astronomical Union’s (IAU) Gazetteer of Planetary Nomenclature. The lunar impact crater registers a northernmost to southernmost latitudinal sprawl of 18.14 degrees north and minus 21.5 degrees south, respectively. Herschel is centered at minus 1.38 degrees south latitude, 111.76 degrees west longitude.

The actual temperature map only approximates “. . . the alignment of the temperatures relative to specific features or coodinates on Mimas . . .” because of the changing geometry that occurred during the map’s creation. “The temperatures were calculated from the brightness of the moon’s infrared heat radiation, measured by CIRS at a wavelength of 12 to 16 microns,” explains Whatmore.

The takeaways for the Mimas temperature map created Feb. 13, 2010, by the Cassini-Huygens spacecraft’s composite infrared spectrometer are that actual temperatures varied unexpectedly from expected temperatures and that an unexpected cold part surrounds the moon’s dominant Herschel Crater.

The Cassini-Huygens spacecraft’s composite infrared spectrometer (CIRS) is a heat-ray detector that covers most of the infrared spectrum; by measuring the strength of different wavelengths of heat rays, the CIRS remotely senses temperatures and distinguishes individual gases via their radiation signatures: courtesy National Aeronautics and Space Administration (NASA), via NASA Cassini at Saturn mission pages

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Upper right image shows unexpected temperature map created from data obtained by the Cassini-Huygens spacecraft’s composite infrared spectrometer (CIRS) on Feb. 13, 2010, the closest-ever flyby of Mimas; lower left image presents Mimas in visible light, with addition of green grid showing latitudes and longitudes at 30-degree intervals; lower right image presents new temperature map on a mosaic of images taken on previous Mimantean flybys; NASA ID PIA12867; image addition date 2010-03-29; image credit NASA / JPL (Jet Propulsion Laboratory) / GSFC (Goddard Space Flight Center) / SwRI (Southwest Research Institute) / SSI (Space Science Institute): May be used for any purpose without prior permission, via NASA JPL Photojournal @ https://photojournal.jpl.nasa.gov/catalog/PIA12867; Generally not subject to copyright in the United States; may use this material for educational or informational purposes, including photo collections, textbooks, public exhibits, computer graphical simulations and Internet Web pages; general permission extends to personal Web pages, via NASA Image and Video Library @ https://images.nasa.gov/details/PIA12867; via NASA Cassini-Huygens mission pages @ https://www.nasa.gov/mission_pages/cassini/multimedia/pia12867.html

The Cassini-Huygens spacecraft’s composite infrared spectrometer (CIRS) is a heat-ray detector that covers most of the infrared spectrum; by measuring the strength of different wavelengths of heat rays, the CIRS remotely senses temperatures and distinguishes individual gases via their radiation signatures: courtesy National Aeronautics and Space Administration (NASA), via NASA Cassini at Saturn mission pages @ https://solarsystem.nasa.gov/missions/cassini/the-journey/the-spacecraft/

For further information:

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