Monday is Mercury day at LPSC. It’s only been a month and a half since Messenger flew past Mercury, and the images and analyses keep on coming. I’m always surprised by the speed and volume of the work that occurs after these planetary missions. Messenger principal investigator Sean Solomon, of Carnegie, began the day’s sessions, and said the team got 500 megabytes of data from its instruments, and 1,213 images.

Most of this stuff has already been reported in the press, in press conferences just after the flyby. And much of the really juicy stuff – understanding the origin and history of Mercury’s magnetic field and tectonics – will have to wait until Messenger settles into orbit around the planet a few years from now.

But I learned a few interesting things. Dave Smith of NASA Goddard noticed an interesting gravity anomaly that was measured as Messenger flew past. The anomaly can’t be explained by twiddling with Mercury’s mass or its equatorial bulge. Smith says it doesn’t necessarily mean that there’s something physical there (such as a high or low density mass that causes the force of gravity to vary slightly). But he says scientists will probably find that Mercury has strange mass concentrations like the moon. MIT’s Maria Zuber later said how Smith’s gravity anomaly happened to coincide with a deep basin that was recorded with the laser altimetry instrument she’s using.

Of all the Mercury pics incorporated into the presenters’ slideshows, the showstopper is still ‘The Spider’ (above). This is a starburst of radial cracks exploding outward from the center of Caloris Basin, one of the largest impact structures in the solar system. Louise Prockter of APL says this find has proved very popular – she’s getting all sorts of ‘imaginative’ suggestions from the public for what could have caused this swarm of cracks. Jim Head of Brown University thinks that they come from dikes below the surface, which at one time were filled with magma that strained and split the crust into the dikes. As the deep interior split a little bit, the crust overhead dropped, creating the radial cracks that are also known as graben (geologists never run out of names for things). “But why would you have this thing in the middle of Caloris Basin, for crying out loud?” Head asks. The original impact that caused Caloris, he says, could have triggered an upwelling of magma.

But the Spider might not last for long. Prockter says they’re already considering changing the name to something more formal. Why do they always have to end up with stuffy, Latin-ized names? One of the potential new names for it is the ‘Parthenon Fossae’.