If humans ever make it to Mars, they might observe incredible green auroras in the sky.
In late Dec. 2014, NASA's MAVEN spacecraft spotted breathtaking auroras in the Red Planet's northern hemisphere. The mission researchers nicknamed them "Christmas lights," and determined they circled the planet near the equator.
"It really is amazing," said Nick Schneider who leads MAVEN's Imaging Ultraviolet Spectrograph (IUVS) instrument team at the University of Colorado. "Auroras on Mars appear to be more wide ranging than we ever imagined."
Unlike Earth, Mars does not have a magnetic field that surrounds the entire planet, but rather boasts "umbrella-shaped" fields that grow from the ground like mushrooms in sporadic patterns. These "magnetic mushrooms" are the remnants of the global field that is believed to have decayed billions of years ago.
"The canopies of the patchwork umbrellas are where we expect to find Martian auroras," Schneider said. "But MAVEN is seeing them outside these umbrellas, so this is something new."
Auroras are formed when energetic particles from space come into contact with a planet's upper atmosphere. On Earth, these auroras guided towards the poles by our global magnetic field, but Mars does not have a stable field; this disorganization means the auroras can form wherever they please.
"The particles seem to precipitate into the atmosphere anywhere they want," Schneider said. "Magnetic fields in the solar wind drape across Mars, even into the atmosphere, and the charged particles just follow those field lines down into the atmosphere."
MAVEN has detected the presence of these auroras, but cannot see them the way a human eye would. This means scientists must find other ways to determine what they would look like to future Martian pioneers. The Martian atmosphere is composed of primarily carbon dioxide, but does contain some oxygen. This suggests excited oxygen particles in Mars' atmosphere would most likely produce green light.
"A diffuse green glow seems quite possible in the Mars sky, at least when the Sun is throwing off energetic particles," Schneider said.
