The "X" above the shard is the camera calibration mark Note the darker center and various shades of grey The cube may be seen in the upper left of the image. Note also the shadow cast by the shard.
The shard is a real artifact in the LO photograph. It has, because of its
shape and size, few mechanisms that could possibly cause it.
Photo defect= low probability because of the structure and shading. There
has been much discussion about this possibility even at NASA. It was felt
that a handling or process artifact could have been introduced in the second
generation negative. NSSDC has reordered a new set of second generation negatives
that will be available later in the year.(Note: Since this was written
I have been informed that the budget for the second generation replacement
has been zeroed out.)
Actual Structure= low to medium probability due to no confirming photo. If
a confirming photo is ever found I would lean heavily on the side of
this explanation. (see Lan Flemings' explanation below.)
Transient Event (outgassing)= high probability at present, because of long
reported LTPs, Apollo 12 and 14 SIDE confirmation, and the lack of a confirming
photo of the shard.
There is a problem with appearance as noted below by Lan and Mike.
Lan Flemings interpretation of the image:
On your comments on the Shard, my objection to the interpretation that it is a plume of liquid water is its shape. It shows no sign of fountaining. Unless the Orbiter captured the plume in the first moments of an eruption, the liquid water at the top should be arcing back toward the surface of the moon. Since liquid water would also be boiling as soon as it was exposed to the vacuum, I would think that there should also be a lot steam and/or ice particle fogging up the entire region, partially or totally obscuring the "Shard" itself. (The "Cube" could possibly be a puff of steam floating off from the "Shard" geyser, but it doesn't really look diffuse enough for a puff of steam or cloud of ice particles, and it has some internal detail (see Mike's gif on the website) that make it look too solid to be a cloud of vapor or ice crystals.
Mike Lomax explanation:
Jon, I really like your interim report. Lan has already addressed the only question I had, and that was about the Shard. The best way for me to see the Shard as a transient event is as ice particles shot out at a relatively high velocity. There would have to be some water, either liquid or vapor, accompanying this ice, but as Lan noted, there is no misty halo around the Shard. If there were a small enough amount of water I suppose the vapor might not have been visible to the LO camera, but even greatly overexposing the image shows no sign of this. Another problem with the 'ice plume' is that the ice would have traveled one-half mile (if we accept the Lan Fleming estimate) vertically with no sign of fanning out at the top. An enormous amount of energy would have been required to account for both the height and the lack of fanning seen here.
The final word from Lan Fleming. (for the time being)
On the various alternatives presented for the Shard, and other objects, I think we can agree that there are alternatives, none of which is conclusive. I have seen nothing that looks like a shadow cast by a .5 to 1-mile high object in the Apollo photographs (AS16-1411, 1412, etc.). The shadow may be too narrow to show up at these distances, but I think the lack of it tends to favor the transient hypothesis, while the lack of fountaining favors the solid structure hypothesis. So I think the conclusion is that we can't reach a definite conclusion yet.
Jon's Preliminary Conclusion: This discussion led me to posit that there were volatiles on the moon, in pockets, waiting for the right set of circumstances to manifest themselves. In other words, Lunar Transient Phenomenon would continue and there had to be a consistant mechanism to explain them. This lead me to question the current model of the dry moon. Then I began to look at the experiments that helped to develop the model and concluded that they were somewhat flawed. It was not because they were badly designed, but because of the location, time available, and techniques used. The assumption of water next to the surface is probably erroneous, but no deep drill core experiments were performed. If performed, these deep drill experiments would have penetrated the impermiable breccia layer and possibly found an aquifer layer. There are indications of multiple lava flows. If regolith was formed between the lava layers then a series of natural aquifers would be formed waiting for the next water influx.