Scientists apply Earth’s hydrothermal plume dynamics to Europa
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.
