Europa's freckles. (Astronomy).

Reddish spots and shallow pits that pepper the surface of Jupiter's moon Europa may mark regions where warmer and less dense ice, possibly from an ocean buffed deep beneath the moon's frigid surface, percolates to the surface.

The spots and pits, each about 10 kilometers in diameter, run across the northern hemisphere of Europa, according to a new analysis of images taken in 1996 and 1998 by the Galileo spacecraft. Dubbed lenticulac, the Latin word for freckles, the uniformly spaced and sized spots suggest that Europa's surface is a thick ice shell floating atop an ocean.

The shell "acts like a planetary lava lamp, carrying material from near the surface down to the [proposed] ocean" and causing material from the ocean to rise to the surface, suggests Robert T. Pappalardo of the University of Colorado at Boulder.

The warm ice that rises to the surface and forms the freckles may reveal the composition of the proposed subsurface ocean and whether it has the ingredients to support life. Even marine organisms that rise to within a few kilometers of the surface could survive, Pappalardo says. If this so-called thick-shell model of Europa is correct, then future spacecraft won't have to drill all the way through the estimated 20km-deep ice shell to search for life in an underlying ocean.

Pappalardo presented the findings Oct. 27 at a meeting of the Geological Society of America in Denver.--R.C.