Starship Asterisk*

cobalthorium-g wrote:
A very similar feature in fact exists on the Moon. It is the "Ina Caldera", a weird 3-km-long feature where the lunar regolith apparently has gone missing and that looks remarkably like these features on Mercury. One of the theories for its formation is outgassing. The March 2012 issue of Sky and Telescope magazine (pg. 10) features a detailed LRO image of it, though it has been know of for decades. I was unable to find a decent image of it on the web.

http://astrobob.areavoices.com/2012/01/30/ina-caldera-one-of-the-moons-coolest-hottest-mysteries/ wrote:

[img3="Ina Caldera sits atop a low, broad volcanic dome or shield volcano, where lavas once oozed from the moon's crust. The darker patches in the photo are blobs of older lunar crust. They're "domed" or higher than the rougher surface below."]http://astrobob.areavoices.com/files/20 ... 5x1024.jpg[/img3]

Ina Caldera – one of the moon’s coolest, hottest mysteries
Posted on January 30, 2012 by astrobob

<<In the March 2012 issue of Sky and Telescope magazine there’s a fascinating short article about a possible lunar volcanic landform called Ina Caldera. This 2-mile long D-shaped patch looks like nothing I’ve ever seen on the moon. Blobs of older, crater-pitted lunar crust rise some 250 feet above the younger, rubbly surface like melted cheese on pizza. Brighter areas on the moon generally indicate younger surface features. Solar and cosmic radiation darkens airless worlds like the moon and asteroids over the long haul of time. The rough area between the “islands” of older crust doesn’t have as many craters either – another sign of its relative youth. Ina was first noticed only as recently as 1971 when photographed by the astronauts aboard Apollo 15. Recent photos taken by the low-flying Lunar Reconnaissance Orbiter (LRO) show a level of detail that reveal how unique this curious feature really is. So what’s going on in Ina?

Theories abound. In a real volcano, calderas are caused by the collapse of material at the volcano’s top after magma from below has drained away following an eruption. Perhaps the top of the low volcanic dome on which Ina sits collapsed unevenly and relatively recently to form the patchwork we see today. Another possibility is that magma from below heated trapped gases like carbon dioxide and water to such high pressures they violently blasted right through the crust, sending rock and debris flying for miles in the moon’s low gravity field.

Other researchers with the LRO mission agree that Ina’s two terrains are a contrast of young and old but don’t think the old bumpy areas are as ancient as assumed. Additional high resolution photos from the orbiter show a good number of craters there, many with soft rims. I encourage you to explore Ina yourself by going to the LRO’s ACT-REACT Quick Map and entering its latitude of 18.65 and longitude of 5.31. As you zoom in, you’ll feel like you’re coming in for a landing.

Whatever happened created an enigmatic moonscape that scientists are still trying to understand. In so many ways, the moon is an undiscovered world. With just six short visits during the Apollo era and 150 lunar meteorites collected on Earth, we’ve barely scraped the lunar regolith.>>

Star*Hopper wrote:Hypothesis: Mercury was a former comet. These hollows are where water/ice boiled off after being caught in Sol's gravity.
~NwCPttstd*hhhh*

Chris Peterson wrote:

Star*Hopper wrote:
Hypothesis: Mercury was a former comet. These hollows are where water/ice boiled off after being caught in Sol's gravity.

Comets are not differentiated bodies; they don't contain iron in significant amounts; they are only a few tens of kilometers in diameter. Mercury is a 5000 km diameter, largely iron body. It was only a comet if we redefine "comet".

Guest wrote:
Looks like the pitting in metal and other normally non-flammable materials that occurs when exposed to concentrated high heat sources...

http://en.wikipedia.org/wiki/Pitting_corrosion wrote:
<<Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the creation of small holes in the metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic while an unknown but potentially vast area becomes cathodic, leading to very localized galvanic corrosion. The corrosion penetrates the mass of the metal, with limited diffusion of ions. The mechanism of pitting corrosion is probably the same as crevice corrosion.

[b][color=#0000FF]Diagram showing a mechanism of localized corrosion developing on metal in a solution containing oxygen[/color][/b]

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[b][color=#0000FF]D A corrosion pit on the outside wall of a pipeline at a coating defect before and after abrasive blasting.[/color][/b]

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This kind of corrosion is extremely insidious, as it causes little loss of material with small effect on its surface, while it damages the deep structures of the metal. The pits on the surface are often obscured by corrosion products. Pitting can be initiated by a small surface defect, being a scratch or a local change in composition, or a damage to protective coating. Polished surfaces display higher resistance to pitting.

Alloys most susceptible to pitting corrosion are usually the ones where corrosion resistance is caused by a passivation layer: stainless steels, nickel alloys, aluminum alloys. Metals that are susceptible to uniform corrosion in turn do not tend to suffer from pitting. Thus, a regular carbon steel will corrode uniformly in sea water, while stainless steel will pit.

The presence of chlorides, e.g. in sea water, significantly aggravates the conditions for formation and growth of the pits through an autocatalytic process. The pits become loaded with positive metal ions through anodic dissociation. The Cl− ions become concentrated in the pits for charge neutrality and encourage the reaction of positive metal ions with water to form a hydroxide corrosion product and H+ ions. Now, the pits are weakly acidic, which accelerates the process.

Besides chlorides, other anions implicated in pitting include thiosulfates (S₂O₃²⁻), fluorides and iodides. Stagnant water conditions favour pitting. Thiosulfates are particularly aggressive species and are formed by partial oxidation of pyrite, or partial reduction of sulfate. Thiosulfates are a concern for corrosion in many industries: sulfide ores processing, oil wells and pipelines transporting soured oils, Kraft paper production plants, photographic industry, methionine and lysine factories.

A single pit in a critical point can cause a great deal of damage. One example is the explosion in Guadalajara, Mexico on April 22, 1992, when gasoline fumes accumulated in sewers destroyed kilometers of streets. The vapors originated from a leak of gasoline through a single hole formed by corrosion between a steel gasoline pipe and a zinc-plated water pipe.>>