Much to NASA’s delight, the NEAR Shoemaker spacecraft continued to transmit data back to Earth for two weeks after it crash-landed on the surface of Eros. Powered by solar cells, NEAR collected gamma-ray data that, once decoded, will help NASA understand the chemical composition of Eros, which they have already begun to believe is a remnant of the early solar system.
The $200 million mission was slated to end on Feb.12. After travelling 2 billion miles since its launch in 1996, NEAR was never expected to last so long. During what would have been the final days of the NEAR mission, NASA had on its hands a functional spacecraft that would soon be space junk. So engineers decided to set NEAR on a collision course with Eros, hoping that the right path would allow NEAR to "softly crash" on the asteriod. After the spacecraft snapped its last image (see Fieldnotes), it hit Eros relatively unharmed.
NASA granted an extension to allow investigators to collect as much information as they could from the mission. Another four day extension was tacked on to that, and shut-down was scheduled for Feb. 28.
The gamma-ray spectrometer (GRS) that survived the crash is able to collect information from as much as 10 centimeters below Eros’ surface. It detects gamma rays from atoms excited by nearby atomic nuclei that are shattered by cosmic rays in space. NEAR scientists can use the GRS data to detect cosmic-ray excited iron, silicon and oxygen; and radioactive potassium, thorium and uranium.
So far, the researchers believe that Eros is undifferentiated and has a composition similar to chondritic meteorites on Earth. The GRS cannot detect sulfur, one of the key volatile elements that, if present, indicates an extraterrestrial body is primitive and has not undergone melting. The presence of potassium supports their initial conclusions, because like sulfur, potassium evaporates when a rock is heated.
NEAR's GRS instrument will be operational for a few more weeks, or until Eros enters the winter phase of its orbit and NEARs solar cells fall into shadow. At that point, scientists will have to wait until November to find out if the spring sun will bring NEAR Shoemaker back to life.