Mysterious lights appeared in the Mexican sky during Friday's massive earthquake.
The quake, which registered a level of 8.4, killed dozens and was the strongest in a century, was accompanied by flashes of green and blue lights shooting throughout the night sky. According to a Google Translate version of an El Universal story, the lights are a naturally occurring electro-magnetic charge, caused by the collapse of the rocks in the ground during the earthquake.
In 2001, NASA scientist Friedmann Freud discovered that "if the stress level (between the rocks) is high, there are electronic loads that momentarily transform insulation rock into a semiconductor." Freud added that the electrical loads are not easy to measure, as they "move with impressive speed, as high as 300 meters per second."
Others aren't so sure, however.
According to a report in The Independent, other experts believe the lights are caused by explosions from power plants or electrical cables.
In the past, the lights have often been confused with UFOs, but Freud discounted that fact.
"In the past, people often interpreted [earthquake lights] in religious terms, and in modern times they thought of UFOs, although there is a completely rational physical explanation that we are working on," he told National Geographic.