2001 Feb 23
NEAR Mission Extended Through February 28
NASA has given the go-ahead for the NEAR mission to collect data from the surface of Eros through Feb. 28, tacking four days onto an extension granted after the NEAR Shoemaker spacecraft's historic landing on the asteroid last week.The extension gives NEAR Shoemaker's gamma-ray spectrometer additional time to observe the elemental composition on and below Eros' surface, and the NEAR team at least two more opportunities to download this information through NASA's heavily used Deep Space Network of antennas.
"This allows us to build a much better sample," says Jacob Trombka, of NASA's Goddard Space Flight Center, team leader for NEAR Shoemaker's X-ray/Gamma-ray Spectrometer. "The longer you accumulate data the more you can reduce the uncertainty of your results. When you look at a little bit of data you see clues, but when you get more data down you can be a bit more definitive."
Touching down on Eros certainly hasn't kept NEAR Shoemaker from touching base with NEAR scientists. The spacecraft has returned readings from its magnetometer, and mission team members are processing the latest information from the gamma-ray spectrometer.
The gamma-ray instrument can measure elemental composition to a depth of about 4 inches, and is much more sensitive on the surface than it was in orbit. Mission engineers fine-tuned the device last week to account for things it hadn't encountered in orbit; it operates at a higher temperature near the surface, for example, because it can no longer radiate heat into space.
"We optimized the instrument for collecting science in its new environment," says John Goldsten, of the Johns Hopkins Applied Physics Laboratory (APL), lead engineer for the gamma-ray spectrometer. We've received the first of three prime data sets and the data is outstanding. This tells us the new commands are working perfectly." The second and third data sets will be transmitted to Earth on Feb. 26 and Feb. 28.
While Trombka says they'll need months to interpret that data, it won't take nearly as long for mission scientists to get a clearer picture of the asteroid's magnetic properties - or lack thereof. NEAR Shoemaker's magnetometer found no evidence of magnetism at its landing site. Having returned data from the surface, the instrument's work is done and it has been turned off.
"We already knew there was no global magnetic field, but measuring this close dramatically increased our ability to see if there was evidence for localized 'hot spots' on the surface," says Brian Anderson, magnetometer instrument scientist at APL. "The landing site shows no evidence for an intrinsic magnetic field. Since the sensor is only two meters above the surface this is a pretty definitive measurement."
