ASTEROID VESTA SHOWS GEOLOGICAL EVIDENCE OF VOLCANISM
Does volcanism exist on Vesta today? Photos from the Dawn Spacecraft orbiting Vesta, the largest asteroid, between Mars and Jupiter, show dikes, fissures, lava flows and volcanoes, that suggest a hot, magnetic and magmatic core.
Radioactive decay for planetary heating is called into question. This would not be possible on an asteroid as tiny as Vesta.
"Spider Crater" shows clear evidence of a dike cutting through with a crack opening up to the right of the dike and probable sulfide magmas being extruded from a molten inner part of Vesta.
I see many beautiful photos of Vesta, but I do not see any explanations forthcoming from NASA, so I will explain to the best of my abilities what we are seeing on Vesta from the many years that I spent mapping as a field geologist. There is much more going on here, on this volcanically active asteroid than anybody so far is prepared to talk or write about. It is very exciting from the geological point of view because it explains how a tiny body like Vesta is heated by spin and changes in its magnetic field (5 hour planetary rotation compared with Earth's 24 hours). We still need verification of Vesta's magnetic field.
Geology 101
A dike or dyke in geology is a type of vertical fissure, usually igneous (like lava, basalt, diorite, dolerite, pegmatite, granite, rhyolite intrusion in a long line compared with a volcano which is near circular intrusion as viewed from above.
End of Geology 101
Now let us look at Vesta in the bottom right hand quadrant of the photo (the south east corner) taken on August 26, 2011 and displayed by NASA on their website on their "image of the day" on September 17, 2011.
http://dawn.jpl.nasa.gov/multimedia/images/imageoftheday/201109/091711_040_thmb.jpg
The dike, which appears as a darker line of about 2-3 kilometers thick runs parallel to the right hand edge of the photo about 30 kilometers in. It dips at about 80 degrees to the east on the photo as can be seen by how the dike does not go straight through the crater, but is shifted downslope (to the east) to the center and then shifted back up the crater as we follow this dike from south to north. The dike then goes north for 30 miles and straight north through "Spider Crater"- my name. This is evidence that the dike is now perpendicular (90 degrees) to the surface at this point. A large fracture has opened up to the east of the dike. A black extrusion in the shape of a fountain or the legs of a spider has cascaded outwards to the southwest, south and south east of this crater, making the crater look like the body of a spider with the legs pointing south. A second dike intersects Spider crater running in a NNW- SSE direction. It also makes a dark line in this crater and a linear row of hills running away from the crater in a NNW direction. There are many thin dikes that truncate the surface of Vesta in this photo, that appear as dark lines. Their direction parallels this second dike in a NNW- SSE direction.
There is also ample evidence of lava flows, small volcanic peaks and heating of one side of craters causing rounding of the crater edge wile the other half remains sharp. See image from NASA on images of the day for September 16, 2011. See large crater in bottom right hand corner.
http://dawn.jpl.nasa.gov/multimedia/imageoftheday/image.asp?date=20110916
This rounding is different from slumping where the craters shape has changed or become elongated. Rounding of the crater edge can only be caused by internal heat that has melted the rock, but preserved the crater shape. This image also shows multiple dikes also in a NNW-SSE direction with respect to the photo, that can clearly be seen be seen south of the slump feature.
CONCLUSION
Vesta has an internal source of heat driving volcanism, caused by its rapid spin and magnetic field interaction. Surface volcanism can also be triggered by a meteorite impact, along planes of weakness (existing dikes), as seen on the image of the day for September 17. This molten inner layer (I will not call it the core at this stage ) is filling the probable tension fractures that are being created by the rapid spin. The tension fractures (now filled with lava and called dikes) are at right angles to the planetary layering or "groves." Sudden meteorite impacts create new volcanism especially in weakened rock alongside dikes as can be seen in "Spider Crater". Vesta is not volcanically dead, but I believe alive today. Spin and magnetism are the source of heat, not radioactive decay.
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