Astronomy Picture of the Day
April 1, 2015

Approaching Rhea (Part I)
Approaching Rhea (Part I)

Credits: NASA/JPL-Caltech/Space Science Institute - Credits for the additional process. and color.: Dr Paolo C. Fienga/LXTT/IPF

After a couple of years spent in High-Inclination Orbits (a circumstance, this one, that limited its ability to encounter Saturn's moons), the NASA Cassini Spacecraft returned to Saturn's Equatorial Plane in March 2015. As a prelude to its return to the realm of the Icy Saturnian Satellites, the NASA Cassini Spacecraft had its first relatively close Fly-By of an Icy moon (apart from Titan) in almost two years, such as on February, 9, 2015. During this encounter, the Cassini's Cameras captured two beautiful images of the Icy moon Rhea, one of which is shown in this image (the second one shall be shown in tomorrow's APOD).


The view we have here is a so-called "Orthographic Projection" of this Celestial Object, and it is facing toward Terrain located on the Trailing Hemisphere of Rhea. Remember that an Orthographic View (or "Projection") of a certain - and given - Celestial Object, is like the view of such a Celestial Object as if it would have been seen by a distant observer, looking through a telescope. However, the view here, has been rotated, so that North on Rhea is up.


This picture is centered at 21° North Latitude and 229° West Longitude of Rhea. The Resolution is roughly 450 meters (such as about 1476 feet) per pixel (---> picture element), and it was acquired at a distance of about 51.200 miles (such as approx. 82.398,208 Km) from the Surface of Rhea.


This frame (which is an Original NASA - CASSINI Spacecraft's falsely-colored and NON Map-Projected image published on the NASA - Planetary Photojournal with the ID n. PIA 19057) has been additionally processed, contrast enhanced, reduced in size to fit the page, Gamma corrected and then re-colorized - according to an educated guess (or, if you wish, an informed speculation) carried out by Dr Paolo C. Fienga - in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Cassini Spacecraft and then looked outside, towards the Northern Latitudes of the Saturnian moon "Rhea"), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team. Different colors, as well as different shades of the same color, mean, among other things, the existence of different Elements (Minerals) present on the Surface of Rhea, each having a different Albedo (---> Reflectivity) and Chemical Composition.


Note: it is possible (but we, as IPF, have no way to be one-hundred-percent sure of such a circumstance), that the actual luminosity of Rhea- as it is in this frame - would appear, to an average human eye, a little bit lower than it has been shown (or, better yet: interpreted) here.



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