NASA has released a satellite image which reveals a strange "thermal anomaly" in the middle of the Atlantic Ocean.
On July 14, 2017, the Suomi NPP satellite snapped a photo (below) showing a portion of South America and the neighboring ocean. Several hundred miles east of the Brazilian coast, you can see an isolated red dot indicating an area flagged by the satellite as being unusually warm, otherwise known as a thermal anomaly.
The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument on Suomi NPP—which is jointly operated by NASA and the National Oceanic and Atmospheric Administration—detects thousands of these anomalies every night, the vast majority of which are caused by fires.
"But obviously a fire isn't burning in the middle of the ocean," Patricia Oliva, a scientist at Universidad Mayor who was previously involved in developing a fire detection algorithm for VIIRS, said in a statement.
So, what then could be responsible for the anomaly?
Natural gas flares sometimes get flagged by VIIRS, however, these only occur in shallow waters near the coast. Similarly, volcanic activity can be marked as an anomaly, but there are no volcanoes anywhere near the red dot on the map.
"It is almost certainly SAMA," Oliva said, in reference to the South Atlantic Magnetic Anomaly.
SAMA is an area where one of Earth's Van Allen radiation belts comes closest to the surface, dipping to an altitude of around 200 kilometers. These belts are zones of energetic charged particles—most of which originate from the Sun—that are captured and held around the planet by its magnetic field.
The magnetic anomaly means that this region of the South Atlantic and any satellites passing above it are exposed to higher than normal levels of radiation. In fact, there are enough high energy particles in the atmosphere here that the developers of the fire-detecting algorithm on VIIRS were surprised by how many thermal anomalies the instrument flagged when they first began using the software.
"Each night, the sensor was detecting several dozen thermal anomalies over the Atlantic Ocean in places that didn't make sense," said Wilfrid Schroeder, the principal investigator for the VIIRS active fire product, said in the statement.
In response, they built a series of filters into the algorithm to remove false signals in this region. Despite this, some still manage to slip through.
"We see probably one or two of these spurious fire detections a night, but remember that is in comparison to the thousands of real thermal anomalies [the] satellite detects each night," Schroeder said. "False fires detections are quite rare."
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