Astronomy Picture of the Day
September 15, 2013

On the Terminator of Europa
On the Terminator of Europa

Credits: NASA/JPL - Voyager 2 Project - Credits for the additional process. and color.: Dr Paolo C. Fienga/LXTT/IPF

This image of the Jovian moon Europa was taken by the NASA - Voyager 2 Spacecraft on July, 9, 1979, when the Probe passed within approx. 225.000 Km (such as about 139.725 miles) from the Frozen Surface of this still mysterious and extremely fascinating Celestial Body. The area shown here is about 600 by 800 Km wide (such as approx. 372,6 by 496,8 miles), and the smallest Surface Features visible in the picture are about 4 Km (such as approx. 2,484 miles) in size.


This image was taken along the Evening Terminator of Europa, and therefore it best shows the Surface Topography of this moon, which is made - among other things - by Complex Narrow Ridges (seen here as Curved Bright Streaks, approx. 5 to 10 Km - such as about 3,1 to 6,2 miles - wide), as well as by Dark Bands, (typically about 20 to 40 Km - such as approx. 12,42 to 24,84 miles - wide and, sometimes, from a few hundreds, to thousands of Kilometers long). Other Surface Features recorded in this image are suggestive (---> could be) of Impact Craters, but they are really rare, thus indicating that the Surface of Europa - which is thought to be dominantly made by Ice - is stil, somehow, active (perhaps it gets periodically warmed-up by the occurrence of a physical phenomenon known as Tidal Friction - or, also, Tidal Heating -: the very same phenomenon that, we believe, keeps (almost) permanently active and restless the Jovian Volcanic moon known as Io).


The larger Jovian Icy Natural Satellites, Callisto and Ganymede, are - evidently - much colder, with way more rigid Crusts, mostly covered by thousands of Ancient Impact Craters. However, the complex intersecting of Dark Markings and Bright Ridges here, on Europa, suggest that the Surface (as well as the Sub-Surface) of this Celestial Body has been (most likely, many times) fractured, and, at the same time (or just a little time after) the fracture occurred, some kind of Material from beneath - Water?!? - welled up (---> surfaced), then it quickly froze, and filled up the Cracks.


Also well visible, at approx. 8 o'clock of the frame, there are other two (but this time - and, as far as we know - still Unnamed) Maculae.


This frame (which is an Original NASA - Voyager 2 Spacecraft b/w image published on the NASA - Planetary Photojournal with the ID n. PIA 01504) has been additionally processed, contrast enhanced, magnified to aid visibility of the Surface details and then re-colorized, according to an educated guess carried out by Dr Paolo C. Fienga/LXTT/IPF, in what they should be its Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Voyager 2 Spacecraft and then looked outside, towards the Jovian moon Europa), 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 others, the existence of different Elements present on the Surface of Europa, each having a different Albedo (---> Reflectivity) and Chemical Composition.


Note 1: 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 Europa - 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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