Astronomy Picture of the Day
January 14, 2013

Features of a Volcanic World
Features of a Volcanic World

Credits: NASA/JPL/Univ. of Arizona - Galileo Project; Credits fo the additional process. and color.: Dr Paolo C. Fienga/LXTT/IPF

Most of the 12 (twelve) frames that form this image-mosaic were taken on February 22, 2000, by the NASA - Galileo Spacecraft; the mosaic covers the Region from Chaac Patera to Camaxtli and Tupan Patera, and at least 11 (eleven) other Paterae (all having different colors, dimensions and morphologies) can easily be seen on the Surface of the Jovian Volcanic moon, Io.

A Patera is an Irregular Depression of the Surface (with or without Scalloped Edges), which does not have the characteristics of an Impact Crater (even though, if seen from a great distance, it may look like one). The Paterae found on Io often correspond to Active Volcanic Centers, and they are, in some ways, quite similar to another relatively common Volcanic Feature: the Calderae.

A Caldera, in fact, it's a large, usually roughly Circular Depression that forms by collapse of the Surface over a shallow Magma Chamber that has been partially emptied by Volcanic Eruptions. In any case, the Paterae on Io are different from the Calderae that can be found and seen elsewhere in the Solar System (like, for instance, on Mars and on our Home Planet Earth)! Io's Calderae, as far as we know, have many Straight Edges and Sharp Angles, thus suggesting that they are related to (caused by) Fractures in the Crust of Io itself and, in many cases, molten Lava can be seen to erupt from (or just lay still on) these deeply unusually-looking Surface Features. However, it has to be said that Planetary Geologists are not yet sure whether the Paterae on Io form over Magma Chambers or if they result from Fractures of (and Movements in) the Crust, with the Lava that - subsequently - follows the Fractures, and so (---> through this "opening") arrives onto the Surface. One of the Paterae (with orange and white materials, located just right of center of the mosaic) shows us what may be thin Plates of Crust that have broken off and rafted over a Lava Lake. Also seen in this mosaic are various dark, bright, and reddish Lava Flows (towards the central-upper left of the frame, to the East of Chaac) that are not confined to the Floor of a specific Patera. The Dark Lava Flows are associated with extremely high temperatures, which are consistent with Lavas that possess Silicate compositions. In fact, all the black areas in this mosaic correspond to high-temperature Hot Spots. The Bright Lava Flows, instead, may actually possess a different composition (such as, for instance, Sulphur) or they may be older Silicate Flows that have been coated by Sulphurous Materials.

Furthermore, the bright dark/yellow and orange Plains surrounding the Volcanic Centers have a "bumpy" texture and the reason could be found in the circumstance that these Plains are (relatively) old, so that their roughness might well represent the final stage of a Geological Process/Activity which took place very slowly and therefore over a long time, rather than the original topography of these Volcanic Deposits. In addition, the Sublimation of Sulphur Dioxide is one process (even at present time occurring on Io) that might have contributed to the formation of the aforementioned "bumpy" (---> highly irregular, with many hillocks and depressions) texture.

The mosaic covers the region from Latitude to 18° North and Longitude from 130° to 160° West, with a total width of approx. 850 Km (such as about 528 miles). The images have a resolution of 186 meters (200 yards) per picture element. The Sun is almost directly overhead (actually, 12° to the South), so most of the brightness variations in this image are due to different types of Surface Materials rather than Topographic Shading.

This picture (which is an Original NASA - Galileo Orbiter false-color image mosaic published on the NASA - Planetary Photojournal with the ID n. PIA 02566) has been additionally processed and then re-colorized in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Galileo Orbiter and then looked down, towards the Surface of the Jovian moon Io), 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 Io, each having a different Albedo (---> Reflectivity) and Chemical Composition.

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