updated 5/9/2005 3:42:22 PM ET 2005-05-09T19:42:22

A European probe circling Mars has hit a snag in the deployment of a water-seeking radar instrument, prompting mission controllers to delay the experiment while engineers investigate the problem.

Flight controllers for the European Space Agency’s (ESA) Mars Express probe halted plans to deploy the second boom in a series of antennas that comprise the spacecraft’s subsurface radar instrument after detecting an anomaly on May 7.

The anomaly occurred as Mars Express completed the deployment of its first radar antenna boom. Of the 13 segments that make up the boom, flight engineers confirmed that only 12 had swung into the proper position. The remaining segment had deployed, but was not positively locked into position and an investigation is underway, ESA officials said.

While flight controllers at ESA’s European Space Operations in Darmstadt, Germany had hoped to deploy all three booms by May 12, the unfurling of the remaining antennas will not resume until engineers fully understand the current anomaly, as well as its implications to future boom deployment.

ESA officials said that the possibility of a deployment delay was not unexpected, and that plans were already in place to reschedule unfurling the second radar antenna in the event of any anomalous events with the first boom.

Mars Express’ antenna booms form the probe’s Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument, a ground-penetrating radar designed to peer beneath the red planet’s surface and scan for deposits of water or ice. The first two booms to be unfurled are dipole antennas each 131 feet (40 meters) long. A third, monopole antenna is 23 feet (seven meters) in length, according to NASA officials at the Jet Propulsion Laboratory (JPL) in Pasadena, California, which is collaborating with ESA on the Mars Express mission.

MARSIS scientists hope their instrument will be able to penetrate up to three miles (five kilometers) beneath Mars’ surface and return distinguishable radar echoes for sand dunes, rock and potential water deposits. The low radio frequencies used by MARSIS will also be tapped to study Mars’ ionosphere and the local effects of solar wind, researchers said.

“The radar gives us two ways to explore the fate of water that once flowed on the surface of Mars,” said Jeffrey Plaut, a MARSIS co-investigator at JPL, in a statement earlier this month. “We will probe beneath the surface for evidence of frozen or liquid reservoirs, and we will study the outer fringes of Mars' atmosphere, where the planet may have lost its water to space."

The MARSIS instrument is one of seven science experiments riding aboard Mars Express, which launched from Earth on June 2, 2003 and reached the red planet in December of that year.

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