Galileo came within 351 kilometers (218 miles) of Europa, and briefly passed behind the frozen moon, the Pasadena, California-based laboratory said in a statement.

When Galileo moved behind Europa, the laboratory said the probe's radio signal to Earth was blocked for a while, allowing scientists to study how signal changed as the craft entered the "silent zone."

Galileo's instruments carried out observations of magnetic fields and charged particles around the moon during Monday's flyby.

"These observations were designed to detect any magnetic disturbances that may occur because of the electrical currents set up in an ocean that may lie beneath Europa's icy crust," the lab said in a statement.

Europa is believed to have a subterranean ocean lying beneath its icy crust, and scientists are keen to find evidence of water on the moon.

"The prospect of a liquid ocean on Europa is intriguing, since water is one of the ingredients essential for life," the lab added.

After the flight over Europa, Galileo was able to observe another three of Jupiter's moons: Amalthea, Thebe, Metis.

Galileo was scheduled early Tuesday to carry out observations of the the moon Io, the most volcanic body in the solar system. It has moved close to Io several times since it began orbiting Jupiter and its satellites in December 1995. The Future of the Galileo Mission January 3, 2000

Meanwhilem NASA Headquarters has agreed in principle to extend the Galileo mission past its planned January 31 finale. Details of funding and itinerary for the new extended mission, to be called the Galileo Millennium Mission, must still be resolved.

The most recent Europa encounter that took place January 3, 2000, is technically still part of the current, extended Galileo Europa Mission. Another Io flyby is planned for February 22, with flybys of Ganymede on May 30 and December 28, and joint observations of Jupiter with the Cassini spacecraft in December 2000.

Galileo engineers like to say that the spacecraft has already lived "well past its warranty", surviving radiation exposure more than twice the level it was designed to withstand.

Although the radiation has created some problems with spacecraft instruments, Galileo is still functioning well. There's no way to predict how long the spacecraft will remain healthy, but as long as it does, it provides valuable opportunities for exploration. In addition, it will serve as a flying testbed of how electronic parts really survive through high radiation exposure over long periods.