Artist's concept of ICESat.
A NASA satellite that spent seven years studying Earth's polar regions ended its successful mission Monday by plunging back to Earth on purpose to burn up in the atmosphere.
Some debris from the Ice, Cloud, and land Elevation satellite ? known as ICESat ? fell into the Barents Sea north of Norway and Russia at approximately 5 a.m. EDT (0900 GMT) Monday, according to the Orbital Debris Program Office at NASA's Johnson Space Center in Houston.
The agency lowered the orbit of ICESat in July and formally decommissioned the satellite in preparation for its re-entry into Earth's atmosphere. But the craft's lasting legacy will be its impact on the understanding of ice sheet and sea ice dynamics, NASA officials said. [Images: Ice of the Antarctic]
Mapping Earth ice from space
The ICESat mission has led to scientific advances in measuring changes in the mass of the Greenland and Antarctic ice sheets, polar sea ice thickness, vegetation-canopy heights, and the heights of clouds and aerosols.
"ICESat has been a tremendous scientific success," said Jay Zwally, ICESat's project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "It has provided detailed information on how the Earth's polar ice masses are changing with climate warming, as needed for government policy decisions."
ICESat data showed the rapid thinning of Arctic sea ice, which provided critical information for revising predictions of how soon the Arctic Ocean might be free of ice in summer, explained Zwally. It also showed how the rate of ice loss from Greenland, which is contributing to the rise in sea level.
"Thanks to ICESat we now also know that the Antarctic ice sheet is not losing as much ice as some other studies have shown," Zwally said.
Using ICESat data, scientists were able to identify a network of lakes beneath the Antarctic ice sheet.
Mission's fiery finale
The orbiting ice sentinel was launched in Jan. 2003 as a three-year mission with a goal of returning science data for five years. It was the first mission of its kind ? specifically designed to study Earth's polar regions with a space-based laser altimeter called the Geoscience Laser Altimeter System.
After 15 laser-operations campaigns and seven years in orbit, the ICESat science mission ended in Feb. 2010 after the failure of the spacecraft's primary instrument.
Mission flight controllers fired ICESat's propulsion system thrusters from June 23 to July 14, safely reducing the lowest point of the spacecraft's orbit to 125 miles (200 km) above Earth's surface.
That orbit then naturally decayed until all remaining fuel on the spacecraft was depleted. The atmospheric drag then slowly lowered ICESat's orbit until it re-entered the atmosphere.
Before its final descent to Earth, mission flight controllers predicted that the vast majority of ICESat would burn up during re-entry.
Of the spacecraft's total mass ? about 2,000 pounds (907 kg) ? only a small percent was expected to reach the Earth's surface.
Some pieces of the spacecraft, weighing 200 pounds (90.7 kg) altogether, were expected to survive, but the risk of any harm caused by this debris was estimated to be very low.
"The ICESat team has done a marvelous job to ensure that the spacecraft is removed as a hazard to other spacecraft and as a potential source of future orbital debris," said Nicholas Johnson, NASA Chief Scientist for Orbital Debris at NASA's Johnson Space Center in Houston.
And, despite the end of ICESat's mission, NASA's observations of Earth's polar regions will continue, agency officials said. NASA has begun development of ICESat-2, currently planned for launch in 2015 and included more advanced instruments.