"The original picture of the plumes as violently erupting Yellowstone-like geysers is changing. They seem more like steady jets of vapor and ice fed by a large water reservoir,"
So they're essentially suggesting a continuous evaporation process, due to the lack of sodium in the vapor cloud. The lack of gravity from such a small object would demand that the continuously growing cloud of vapor could not remain captured by the moonlet, else it would have a thick atmosphere.
Perhaps this moon was the size of Jupiter (or larger) in it's past, given that our solar sytem is "Billions" of years old, right?
Either that, or the rate of vaporization has changed (i.e. dramatically sped-up recently)
Or perhaps this moon is a new arrival, trekking across the galaxy with a big load of water until it was captured in our solar system.
Or, heretically, our solar system is considerably newer than speculated upon by many.
I would bet that something has changed, but what. I know that they have been theorizing that this is being caused by a pocket of radioactive material; it's possible that this was shifted closer to the surface do to seismic activity.
A water ice comet, captured long ago might end up that way.
Er, you really don’t have any concept of the size of astronomical masses, do you? Billions of years of leakage isn’t all that much for an ice ball the size of Arizona.