Invisible auroras may light up 'the whole night sky' on Mars
Scientists have observed a completely unique type of aurora on the red planet using the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, according to new research published on November 5 in the journal Science.
"It's possible the new type of aurora lights up the whole night sky over the planet," Dave Brain, a MAVEN researcher, said during a NASA press conference on Thursday.
Auroras happen when high-speed, electrically charged particles from the sun slam into a planet's atmosphere. The air molecules absorb that energy and quickly release it as photos of light.
Oxygen molecules emit greenish-yellow light or red light, and sometimes ultraviolet (UV) light - which is invisible to the naked eye. Nitrogen, the most common gas in Earth's atmosphere, can emit blueish light. These dazzling light shows happen only around the northern and southern poles on Earth, since the shape of its magnetic field pulls the charged particles into those regions.
Auroras on Mars are unique because the planet doesn't have a concentrated, polar magnetic field like Earth's. Instead, the Martian magnetic field is weak and diffuse, likely because a strong, ancient, and Earth-like magnetic field imprinted itself in metallic Martian rocks before it faded away eons ago.
"Given minimal magnetic fields over most of the planet, Mars is likely to exhibit auroras more globally than Earth," the researchers write in the paper.
The illustration below shows how auroras (purple) concentrate around Earth's poles compared to auroras on Mars, which are spread out:
So why haven't we detected Martian auroras until now?
The study suggests most of the light is UV and invisible to our eyes. Instruments on Earth that can detect UV probably haven't seen it, either, because the ozone layer absorbs most UV light. Mars also has 1% the atmospheric pressure of Earth, so there is less air for solar particles to slam into - the diffuse aurora appeared fairly dim to MAVEN, which can detect UV light.
Auroras on Mars probably emit some visible light but likely too little to see from Earth. Perhaps the first person on Mars could look up at the night sky there and tell us for certain.