[X] My Assistant

[nprev]

An ambitious astronomer takes advantage of a rare opportunity to photograph the hemisphere of Mercury we almost never get to see via telepresence in Chile. Article here.

[dvandorn]

The most common theory I've heard in re Mercury is that it encountered one or more "big whack"-sized impacts, but that being so close to the Sun and being intrinsically less massive than Earth or Venus, a majority of the ejected material (including most of Mercury's original crust and mantle) never re-accreted onto the planet.

With only a small percentage left of its original silicate mantle, I can imagine that volcanic processes on Mercury would have resulted in landforms that don't look distinctively volcanic -- especially when compared to bodies such as Earth, Luna or Mars.

For example, let's say that only the densest portion of Mercury's mantle was retained. This, and the crystallization of the outer layers of the remnant mantle to form a new crust, could leave only highly viscous, iron-rich lavas available for subsequent extrusion. And since the new crust formed late in the accretion process, you don't see big pile-ups of lava -- as it extruded onto the already thin crust, the whole thing flattened out and the flow features were made very subtle. Thus the distinctive, low-and-rolling landforms of the intercrater plains.

-the other Doug