Astronomy Picture of the Day
September 6, 2012

Approaching Europa
Approaching Europa

Credits: NASA - Voyager 1 Project; Credits fo the additional process. and color.: Dr Paolo C. Fienga/LXTT/IPF

Today's APOD is another view of the mysterious Jovian moon Europa, that was taken by the NASA - Voyager 1 Spacecraft from a range of approx. 2.870.000 Km (such as about 1,6 MMs). The side of Europa that you can see here, is that one that always faces away from Jupiter (remember that Europa, just like our Moon - as well as almost all the moons of the Solar System - is trapped in a "Tidal Locking" (or "Captured Rotation") with Jupiter. The Tidal Locking is a phenomenon that occurs when the Gravitational Gradient makes one side of a Celestial Body always face another Celestial Body: an effect also known as "Synchronous Rotation".

In other words, a Celestial Body that is tidally loked to another one needs, to rotate around its own Axis, just as much time as it needs to revolve around its Parent Planet (and this situation causes one Hemisphere of the "trapped" Celestial Body to constantly face the Parent Planet). Usually, the tidally loked Celestial Body/ies, in any given Planetary System, is/are the smaller one/s; but, if the difference in mass between the different Bodies - as well as their physical separation (---> the distance between them) is (relatively) small, then each one of them may end up being tidally locked to the other/s (as it seems to be the case, for instance, of Pluto and Charon - we cannot say, at present time, if even the other moons of Pluto are tidally locked too, but it seems reasonable to assume so).

Back to today's picture, notice that the irregular dark and bright patches that can be seen on the Surface of Europa are deeply different from those (however similar) patterns visible on other Jovian moons as well as from those that can be found on the Moon, Mars and Mercury. The Dark Intersecting Lines criss-crossing most of the Surface of Europa, instead, are Faults (---> breaks in the Crust).

This frame has been additionally processed and then re-colorized, according to an informed speculation carried out by Dr Paolo C. Fienga (LXTT-IPF), in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Voyager 1 Probe 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.

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