Posted by Kyle Brookings on Thursday, November 1, 2018
On July 14, 2017, the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured this night image of the South Atlantic. The red dot several hundred kilometers off the coast of Brazil is a thermal anomaly—an area of Earth’s surface flagged by the satellite as being unusually warm.
Of the thousands of thermal anomalies that VIIRS detects each night, the vast majority are caused by fires. “But obviously a fire isn’t burning in the middle of the ocean,” said Patricia Oliva, a scientist at Universidad Mayor who helped develop a fire detection algorithm for VIIRS when she was at the University of Maryland. Natural gas flares also trigger thermal anomalies, but they are only found in shallow waters near the coast. Volcanic activity can light up the satellite as well, but there are no volcanoes anywhere near this area.
“It is almost certainly SAMA,” Oliva said, using an acronym for the South Atlantic Magnetic Anomaly. This weakness in Earth’s magnetic field, centered over South America and the South Atlantic, allows one of Earth’s Van Allen radiation belts—zones of energetic particles trapped by the magnetic field—to dip closer to the atmosphere. As a result, much of South America and part of the South Atlantic Ocean get an extra dose of radiation.
While the atmosphere blocks most high-energy particles, and they do not cause problems at the surface, there are enough of them in the space close to Earth to cause issues for the electronics systems of spacecraft. The International Space Station has extra shielding because of SAMA, and the Hubble Space Telescope powers down its science instruments when it passes through the region.