A DC-8 rumbles down the runway in Punta Arenas, Chile, bound once again for the fickle weather of Antarctica. Chock full of scientific equipment, the nearly 48-meter-long plane—the core of NASA's Operation ICE Bridge—will fly as low as 300 meters above the glaciers and valleys of West Antarctica as well as the ice just off shore. Employing gravimeters, laser altimeters, even radar, the plane will attempt to get a handle on the rapid thinning of the Antarctic ice sheet—as well as fill in for the aging ICESat 1 satellite that is soon to be defunct.

"We want to monitor the change along the edge of the ice sheet, particularly the outlet glaciers that are critical for stability," says geophysicist Michael Studinger of Columbia University's Lamont–Doherty Earth Observatory, and a member of the ICE Bridge team. "This is, of course, an important process, because the ice that melts there ends up in the ocean and raises sea level."

He adds: "the closer we look, it seems like not only is the melting taking place faster than we thought, it's also penetrating inland farther than we thought. … It's not so much air temperatures but warmer water underneath that is melting these ice sheets."

The campaign of 17 flights this season—wrapping up by the end of November—will cost $7 million but will offer one advantage over space-based observations: detailed measurements of ice thickness via radar.

And until a successor to ICESat 1 is launched, probably in 2014, according to NASA, the flights will continue—for instance, to Greenland in spring 2010 and back to Antarctica next fall. In the meantime, Studinger says, the meltdown "seems to be accelerating."