WASHINGTON - To help figure out what's happening inside the fastest-moving Greenland glacier, a US rocket scientist sent 90 rubber ducks into the ice, hoping someone finds them if they emerge in Baffin Bay.

The common yellow plastic bath toys are one part of a sophisticated experiment to determine why glaciers speed up in the summer in their march to the sea, said Alberto Behar of NASA's Jet Propulsion Laboratory in California.

The Jakobshavn Glacier is very likely the source of the iceberg that sank the Titanic in 1912 and researchers focus on it because it discharges nearly 7 percent of all the ice coming off Greenland. As the planet warms, its melting ice sheet could make oceans rise this century.

"It's a beautiful place to visit. You can watch these icebergs continuously march across and fall into the ocean," Behar said.

What you can't see is how melting water moves through the ice.

"Right now it's not understood what causes the glaciers themselves to surge in the summer," Behar said. One theory is that the summer sun melts ice on the top glacial surface, creating pools that flow into tubular holes in the glacier called moulins.

The moulins can carry some water all the way to the underside of the glacier, where it acts as a lubricant to speed the movement of ice toward the coast. But because it cannot be seen, no one really knows what occurs.

That's where the rubber ducks come in, along with a probe about the size of a football loaded with a GPS transmitter and instruments that can tell much about the glacier's innards.

In August, Behar flew by helicopter to a place on the glacier where rivers of melted ice flow into moulins.

Researchers lowered the probe into one moulin by rope and released it into the water flowing beneath the ice.

They also released the flotilla of rubber ducks, each labeled with the words "science experiment" and "reward" in three languages, along with an e-mail address.

The ducks - if they are found and if somebody e-mails the discovery - would tell scientists where the water ends up.

The probe could tell much more.

First, it would signal its position via GPS. Its pressure and temperature sensors would supply information. And an accelerometer - which records how much things speed up or slow down - could point to waterfalls or cascades, features that would make the probe, and the water, go faster.

Behar said he hoped a fisherman or hunter might find a duck or the probe but so far nothing has turned up.

"We haven't heard back but it may take some time until somebody actually finds it and decides to send us an e-mail that they have found it," he said. "These are places that are quite remote so there aren't people walking around."

As a creator of robotic rovers for NASA, Behar often tests vehicles meant for space in hostile places on Earth. He worked with Konrad Steffen of the University of Colorado, a specialist on Arctic ice and the Greenland ice sheet.

© Copyright 2008 Globe Newspaper Company.