Passing probe to study 'crop circles' on Europa

When NASA's New Horizons space probe makes its closest approach of Jupiter at 0543 GMT (0043 EST) on Wednesday, it will get the best ever glimpse at the composition of several of the planet's large moons.

The Pluto-bound probe will be the only spacecraft to visit the giant planet between 2003 and 2016. Watch an animation of the Jupiter flyby.

New Horizons is already making between 15 and 20 observations per day. But to allow the spacecraft to keep gathering data and not turning its antenna back to Earth, NASA plans to send back only five images of Jupiter and its moons shortly after the flyby.

One of those five will be of Jupiter's moon, Europa, which scientists think harbours a watery ocean beneath an icy crust. Some scientists say this is a prime place to look for life in the solar system. ...

With a resolution of 15 kilometres per pixel, New Horizons will try to spy large circular grooves on the surface of Europa's ice shell - "one of the oddest features we don't know much about", says John Spencer, deputy lead for the spacecraft's scientific observations of the flyby.

The Galileo spacecraft, which launched in 1989 and studied Jupiter until 2003, spotted these symmetrical features, jokingly referred to by the science team as "crop circles". It seems the shell has been warped by some activity beneath the ice, but scientists have not been able to pinpoint what that is. "It's not obviously related to any tidal deformation," says Bill McKinnon, a planetary scientist at Washington University in St Louis, Missouri, US.

The circles and arcs can be hundreds of kilometres across, but they are faint. So for observational purposes, it helps to look at them near sunset and sunrise, when the shadows they cast on the surface are long.

•	Passing probe to study 'crop circles' on Europa NewScientist.com (UK), Tuesday, Feb. 27, 2007 Byline: Kelly Young, NewScientist.com news service