A type of aurora in Mars -- first identified by NASA's MAVEN spacecraft in 2016 -- is the most common form of the lights occurring on the Red Planet, according to a study which can help track water loss from the Red Planet's atmosphere.
The study, published in the Journal of Geophysical Research - Space Physics, noted that aurora on the Earth are commonly seen as colourful displays of light in the night sky near the polar regions.
However, the researchers from NASA's Goddard Space Flight Center (GSFC) in the US, said the phenomenon on Mars, called a proton aurora, happens during the day and gives off ultraviolet light.
They said it is invisible to the human eye but detectable to the Imaging UltraViolet Spectrograph (IUVS) instrument on the MAVEN -- Mars Atmosphere and Volatile EvolutioN -- spacecraft.
The spacecraft's mission is to investigate how Mars lost much of its atmosphere and water, transforming its climate from one that might have supported life to one that is cold, dry, and inhospitable.
According to the researchers, the proton aurora is generated indirectly by hydrogen derived from Martian water which is in the process of being lost to space.
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So they said this aurora could be used to help track ongoing Martian water loss.
"In this new study using MAVEN/IUVS data from multiple Mars years, the team has found that periods of increased atmospheric escape correspond with increases in proton aurora occurrence and intensity," said Andrea Hughes of Embry-Riddle Aeronautical University in the US.
The study noted that the proton aurora form when the sub atomic particles, protons, from solar winds interact with the upper atmosphere on the dayside of Mars.
Approaching Mars, the researchers explained that these protons transform into neutral atoms by stealing electrons from hydrogen atoms in a huge gas cloud surrounding the Red Planet.
When the high-speed incoming atoms hit the Martian atmosphere, some of their energy is emitted as ultraviolet light, the NASA scientists said.
During southern summer on Mars, the planet is near its closest distance to the Sun in its orbit and huge dust storms can occur, they added.
The summer warming and dust activity seem to cause proton auroras by forcing water vapour high in the atmosphere, according to the researchers.
These water molecules are broken by the solar extreme ultraviolet light into its components -- hydrogen and oxygen.
The researchers explained that the light hydrogen is weakly bound by Mars' gravity and enhances the hydrogen gas cloud surrounding Mars, increasing the element's loss to space.
"Also, the connection between MAVEN's observations of increased atmospheric escape and increases in proton aurora frequency and intensity means that proton aurora can actually be used as a proxy for what's happening in the hydrogen corona surrounding Mars, and therefore, a proxy for times of increased atmospheric escape and water loss," Hughes added.
The study noted that as the hydrogen interactions with solar-wind protons become more common, the Martian aurora becomes more frequent and brighter.
"Perhaps one day, when interplanetary travel becomes commonplace, travellers arriving at Mars during southern summer will have front-row seats to observe Martian proton aurora majestically dancing across the dayside of the planet (while wearing ultraviolet-sensitive goggles, of course). These travelers will witness firsthand the final stages of Mars losing the remainder of its water to space," Hughes said.