Cassini Wide Angle Camera Imaged South Pole During First Titan Flyby

Summary: The Cassini wide angle camera imaged the south pole during the first Titan flyby on Friday, July 2, 2004.

Natural color image composites Cassini wide angle camera’s blue, green and red filtered images obtained July 2, 2004, from an approximate distance of 347,000 kilometers (216,000 miles); yellow curve on image with superimposed coordinate system grid (right) indicates day/night terminator; image scale equals 21 kilometers (13 miles) per pixel; phase angle of 62 degrees; NASA ID PIA06087; image addition date 2004-07-27; image credit NASA / JPL / Space Science Institute: May be used for any purpose without prior permission, via NASA JPL Photojournal

The Cassini wide Angle Camera imaged the south pole during the first Titan flyby on Friday, July 2, 2004, as the Cassini-Huygens spacecraft took the mission’s first images of Saturn’s largest moon.

The Cassini Wide angle camera (WAC) is one of two framing cameras composing the Cassini Imaging Science Subsystem (ISS). The two-dimensional imaging device pairs the wide angle camera with a narrow angle camera (NAC). The Cassini Imaging Science Subsystem is mounted on the Cassini-Huygens spacecraft’s Cassini orbiter. The sophisticated camera system numbers among 12 science instruments carried on the Cassini orbiter.

The mission’s wide angle camera is a 0.2-meter (200-millimeter) focal length refractor telescope with a field of view (FOV) of 3.5 degrees. Both the wide angle camera and the narrow angle camera are outfitted with an array of spectral filters that combine to yield an electromagnetic spectrum span of 200 to 1100 nanometres (nm), according to Cassini imaging administrator Carolyn Porco and 19 co-authors in the November 2004 issue of Space Science Reviews. (A nanometer is a unit of length in the metric system equating to one billionth of a metre.)

On July 2, 2004, the Cassini-Huygens spacecraft made its first flyby of Titan. The NASA Jet Propulsion Laboratory’s (JPL) Photojournal website’s gallery of images from the first Titan flyby includes two natural color images, NASA identification numbers PIA06087 and PIA 06089.

A natural color image captured by Cassini’s wide angle camera on July 2, 2004, reveals the view of the largest Saturnian moon only about two hours after the spacecraft’s closest approach to Titan. The natural color image (NASA ID PIA06087) represents a composite of images taken through the wide angle camera’s blue, green and red filters. The color-filtered images were obtained at an approximate distance of 347,000 kilometers (216,000 miles) from Titan.

The phase angle from the sun to the target, Titan, to the observer, the Cassini-Huygens spacecraft, measured 62 degrees. In her Planetary Society blog posting Oct. 27, 2009, planetary geologist Emily Lakdawalla notes that, per planetary scientist Anne Verbiscer’s communication, Titan displays no variability in brightness at phase angles under 90 degrees, that is, below the half moon phase.

Titan appears as a gibbous moon, more than half-illuminated, in the July 2 natural color image. Illumination encompasses an expanse of Titan southward from the equator to the south pole and eastward from approximately 330 degrees west longitude. The day/night terminator is clearly visible as the line marking the boundary between Titan’s illuminated and unilluminated regions.

A second natural color image displayed on the NASA JPL Photojournal website represents the view of Titan on July 3, 2004, approximately one day after the first Titan flyby’s closest approach. The natural color image (NASA ID PIA06089) composites images obtained through the wide angle camera’s blue, green and red filters. The July 3 color-filtered images were taken at an approximate distance of 790,000 kilometers (491,000 miles) from Titan. The images were acquired at a sun-Titan-spacecraft, or phase, angle of 115 degrees. The phase angle of the July 3 color-filtered images measured 115 degrees.

The July 3 natural color image presents Titan as a crescent moon. Titan’s illuminated portion stretches along the eastern limb from the south pole northward to the lower crescent’s point, or horn, at approximately minus 30 degrees south latitude and the upper horn, in northern equatorial latitudes. The Titanean terminator demarcates the image’s vast unilluminated region, which encompasses approximately 180 to 300-plus degrees west longitude and minus 60 degrees south latitude to 30-plus degrees north latitude.

The takeaways for the Cassini wide angle camera’s south pole images during the first Titan flyby in July 2004 are that two natural color images displayed on the NASA Jet Propulsion Laboratory’s (JPL) Photojournal website show the Titanean south pole in the moon’s crescent and gibbous phases; that the July 2 image composites blue, green and red filter images obtained from an approximate distance of 347,000 kilometers (216,000 miles); and that the July 3 image’s view was acquired from an approximate distance of 790,000 kilometers (491,000 miles).

Natural color image composites Cassini wide angle camera’s blue, green and red filtered images obtained July 3, 2004, from an approximate distance of 790,000 kilometers (491,000 miles); yellow curve on image with superimposed coordinate system grid (right) indicates day/night terminator; image scale equals 47 kilometers (29 miles) per pixel; phase angle of 115 degrees; PIA06089; image addition date 2004-07-28; image credit NASA / JPL / Space Science Institute: May be used for any purpose without prior permission, via NASA JPL Photojournal

Acknowledgment

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

Image credits:

Natural color image composites Cassini wide angle camera’s blue, green and red filtered images obtained July 2, 2004, from an approximate distance of 347,000 kilometers (216,000 miles); yellow curve on image with superimposed coordinate system grid (right) indicates day/night terminator; image scale equals 21 kilometers (13 miles) per pixel; phase angle of 62 degrees; NASA ID PIA06087, image addition date 2004-07-27; image credit NASA / JPL / Space Science Institute: May be used for any purpose without prior permission, via NASA JPL Photojournal @ https://photojournal.jpl.nasa.gov/catalog/PIA06087

Natural color image composites Cassini wide angle camera’s blue, green and red filtered images obtained July 3, 2004, from an approximate distance of 790,000 kilometers (491,000 miles); yellow curve on image with superimposed coordinate system grid (right) indicates day/night terminator; image scale equals 47 kilometers (29 miles) per pixel; phase angle of 115 degrees; PIA06089, image addition date 2004-07-28; image credit NASA / JPL / Space Science Institute: May be used for any purpose without prior permission, via NASA JPL Photojournal @ https://photojournal.jpl.nasa.gov/catalog/PIA06089

For further information:

Lakdawalla, Emily. “What ‘Phase Angle’ Means.” The Planetary Society > Blogs. Oct. 27, 2009.
Available @ https://www.planetary.org/blogs/emily-lakdawalla/2009/2179.html

Lavoie, Sue, site mgr. “PIA06081: Titan in Natural Color.” NASA Jet Propulsion Laboratory Photojournal > Catalog > Saturn. Image addition date 2004-07-02.
Available @ https://photojournal.jpl.nasa.gov/catalog/PIA06081

Lavoie, Sue, site mgr. “PIA06089: Hazy All Over.” NASA Jet Propulsion Laboratory Photojournal > Catalog > Saturn. Image addition date 2004-07-28.
Available @ https://photojournal.jpl.nasa.gov/catalog/PIA06089

Levy, David H. Skywatching. Revised and updated. San Francisco CA: Fog City Press, 1994.

Marriner, Derdriu. “Cassini Narrow Angle Camera Imaged South Pole During First Titan Flyby.” Earth and Space News. Wednesday, July 4, 2012.
Available @ https://earth-and-space-news.blogspot.com/2012/07/cassini-narrow-angle-camera-imaged.html

Marriner, Derdriu. “Christiaan Huygens Discovered Saturnian Satellite Titan March 25, 1655.” Earth and Space News. Wednesday, March 21, 2012.
Available @ https://earth-and-space-news.blogspot.com/2014/03/christiaan-huygens-discovered-saturnian.html

Marriner, Derdriu. “Visible and Infrared Mapping Spectrometer VIMS Shows Titanean Surface.” Earth and Space News. Wednesday, March 28, 2012.
Available @ https://earth-and-space-news.blogspot.com/2012/03/visible-and-infrared-mapping.html

Moore, Patrick, Sir. Philip’s Atlas of the Universe. Revised edition. London UK: Philip’s, 2005.

Porco, Carolyn C.; Robert A. West; Steven Squyres; Alfred McEwen; Peter Thomas; Carl D. Murray; Anthony Delgenio; Andrew P. Ingersoll; Torrence V. Johnson; Gerhard Neukum; Joseph Veverka; Luke Dones; Andre Brahic; Joseph A. Burns; Vance Haemmerle; Benjamin Knowles; Douglas Dawson; Thomas Roatsch; Kevin Beurle; and William Owen. “Cassini Imaging Science: instrument Characteristics and Anticipated Scientific Investigations at Saturn.” Space Science Reviews, vol. 115 (November 2004), issue 1-4: 363-497.
Available via NASA GISS (Goddard Institute for Space Studies) @ https://pubs.giss.nasa.gov/docs/2004/2004_Porco_po04100j.pdf