March 21, 2012
Credits: NASA/JPL - Credits for the additional process. and color.: Dr Paolo C. Fienga/Lunar Explorer Italia/IPF
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The bright Cirrus-like Clouds of the Gas-Giant Planet Neptune change very rapidly, often forming and dissipating over relatively short periods of time (from several to tens of hours). In this two frames taken by the NASA - Voyager 2 Spcacecraft, we can observe some "Cloud Evolution" in the Neptunian Region which is around the so-called "Great Dark Spot (or GDS for short)": a gigantic and, most likely, permanent hurricane which is, in a way, the Neptunian equivalent of Jupiter's Great Red Spot. The color difference between the two "Great Spots" is to be found, we believe, not only in the chemical elements which form and, at the same time, make the Jovian and the Neptunian Atmospheres slightly different from each other (as a matter of fact, the Neptunian Atmosphere is thought to be mainly composed by Hydrogen - in a percentage of approx. 85% -, Helium - about 13% - and Methane - about 2% -, while the Jovian Atmosphere is composed by Hydrogen - for over 90% - and Helium - for about 10%), but also by the strongly different conditions of Solar Illumination and Heating that exist between these two fascinating Celestial Bodies (consider that the mean distance of Neptune from the Sun - which is approx. 4.504.300.000 Km - is way greater than Jupiter's one - that is 778.330.000 Km "only"...) as well as by the different average Atmospheric Pressure of the two Gas-Giant Planets (which is approx. 0,7 bars for Jupiter and about 3 bars for Neptune). All that, whitout forgetting their mean Orbital Velocity as well as the so-called "Tilt" of their Axis (the mean Orbital Velocity for Neptune is about 5,5 Km/sec while the Jupiter's one is approx. 13 Km/sec and the Tilt of the Jovian Axis is only 3,13° while the Neptunian one is 29,56°), which makes Jupiter a substantially "season-free" Planet and Neptune a world where seasons actually occur, thus making the Planet to be and to look different, as time goes by and its orbit around the Sun proceeds (and, of course, no matter how distant Neptune is from our Parent Star). The surprisingly rapid changes that have occured in the Neptunian Upper Atmosphere (like it is clearly proven by these two frames) also show that in that Region the weather is perhaps as dynamic and variable as it is the Earth's one. However, the scale of the entire scene is immense by our standards: just consider, for instance, that the Earth and the Great Dark Spot are of similar size...It must also be said, though, that in Neptune's frigid Atmosphere, where temperatures are as low as 55 degrees Kelvin (such as -218° Celsius), these Cirrus-like Clouds should be composed of frozen Methane, rather than crystals of Water Ice. The predominant blue color of this Gas-Giant Planet is a result of the absorption of Red and InfraRed Light by Neptune's Methane Atmosphere. Clouds elevated above most of the Methane Absorption Atmospheric Layer appear white, while the very highest Clouds tend to be yellow-red. Neptune's powerful Equatorial Jets - where Winds blow at nearly 900 miles per hour! - are centered on the so-called "Dark Blue Belt" (not visible in this frame) that is located just South of Neptune's Equator. Farther South, a very light "Green Belt" (visible in a few HST color-enhanced pictures) indicates a Region where the Neptunian Atmosphere absorbs Blue Light. This frame has been colorized in Absolute Natural Colors by (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Voyager 2 Spacecraft and then looked towards Neptune), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team. |
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