The size of ice domes and movement of ice rafts on the surface of Europa, one of Jupiter's moons, are consistent with what one could expect of melting caused by a hydrothermal vent plume, or plumes, in an ocean beneath the ice, say oceanographers John Delaney of the University of Washington and Richard Thomson of Fisheries and Oceans Canada.

Scientists know that Europa has a layer of water on its surface that is perhaps 100 kilometers (60 miles) deep, making it nearly 10 times deeper than any of Earth's oceans. The thickness of the frozen surface continues to be debated.

If hydrothermal vent plumes are contributing heat to Europa's ocean, Delaney and Thomson estimate that the frozen surface of the ocean actually may be 3 to 5 kilometers (2 to 3 miles) thick on average -- instead of the 20 kilometers (12 miles) some have estimated. And it makes it all the more possible that researchers may find microorganisms living in vent fluids on Europa, as they do here on Earth.

Delaney and Thomson's model, the first to take what's known about plume dynamics on Earth and apply them to Europa, was the subject of a paper last year in the Journal of Geophysical Research and a presentation at December's American Geophysical Union meeting.

The possibility of life on Europa will be part of Delaney's presentation, "Volcanoes, Oceans and Life in the Solar System," a lecture that is free and open to the public Jan. 23, 7 p.m., Room 210, Kane Hall. His talk is the second in the "Oceans to Stars Lecture Series" offered by the UW's College of Ocean and Fishery Sciences and School of Oceanography.

Among scientists interested in Europa, a number think tidal forces generated by the gravitational tug-of-war between Jupiter, Europa and neighboring moons Io and Ganymede cause tidal flexing of Europa's icy crust, friction and then melting. Delaney, Thomson and others hypothesize that tidal flexing is at work on Europa's rocky core generating heat and magma.

Delaney and Thomson's model is the first:

• To estimate Europa's global heat flux through calculations that compare it with the flux from another of Jupiter's moons, Io, where measurements are far more accurate because there is no shroud of ice. They estimate Europa's heat flux is about a third of that from the Earth's seafloor.
  
  
• To describe how Europa's rotation and weak stratification of its ocean might keep a hydrothermal vent plume from dispersing. The scientists describe a plume continuously rising like a cyclone through 100 kilometers of ocean to reach the base of the ice.
  
  
• To determine that a plume, or plumes, only needed to focus 1 percent of Europa's estimated global heat flux for about 1,000 years to melt through 5 kilometers of ice and cause the ice rafts in the Conamara Chaos region on Europa. There are numerous possible examples on Earth of such steady-state hydrothermal venting, Thomson and Delaney say. The main vent site at the Endeavour segment of the Juan de Fuca Ridge off the west coast of Canada and the United States, for instance, may have persisted for thousands of years based on the composition and diversity of the biological community found there.

If the melting at the surface of Europa is caused in part by plumes from magma-heated regions of the seafloor, it is feasible that some of the dark materials observed on the surface of Europa, thought to be salts and hydrated sulfuric acid, are remnants of particle-laden plumes originating from the seafloor.

Delaney says a better understanding of the links between plate-tectonic processes on our own planet and the microbial life that flourishes near faults, fissures, vent structures and beneath the Earth's crust will help us seek life on other planets and moons.

He and Thomson are part of a consortium of researchers from Canada and the United States interested in using 2,000 miles of electro-optical cable -- cable that can carry power, instructions to remote instruments and data sent back from those instruments -- to wire the whole Juan de Fuca Plate off our coast. The Juan de Fuca is one of a dozen or so major tectonic plates that make up the surface of the Earth. Thousands of instruments, including tiny subs and probes that could be maneuvered by scientists back on land, would be stationed at 30 experimental sites along the cable network as part of Project Neptune.