The auroras of Earth are a massive wonder, but our planet isn''t the only place in the Solar System where these phenomena are discovered.
A metallic glow, although sometimes in unusual wavelengths, has been discovered at every planet except Mercury, and some moons of Jupiter... and even a comet. But Mars is where it becomes interesting. An important component of the red planet is its global magnetic field, which has a major role in the formation of Aurora elsewhere.
Regions of localized magnetic fields have sprouted from some areas of the crust, especially in the southern hemisphere. New evidence has found that these small, local magnetic fields have interacted with the solar wind in interesting ways to produce Mars''sdiscrete (or structured) ultraviolet auroras.
"We have the first extensive study to investigate how solar wind conditions affect auroras on Mars," said a physicist and astronomer Zachary Girazian of the University of Iowa.
"Our main finding is that inside the strong crustal field region, the aurora occurrence rate depends mostly on the orientation of the solar wind magnetic field, while outside the strong crustal field region, the occurrence rate depends mostly on the solar wind dynamic pressure."
Auroras borealis and australis are a fairly good way to depict them when particles from the solar wind collide with Earth''s magnetosphere, and are then accelerated along the lines of the magnetic field to high latitudes, where they plummet into the upper atmosphere.
They also interact with atmospheric particles to produce the shimmering lights that float across the sky.
The occurrences are shaped in similar ways on other organisms, according to evidence. For example, Jupiter''s powerful, permanent auroras are also facilitated by the enormous planet''s magnetic field.
The global magnetic field of Mars was relatively early on in the planet''s history, leaving behind only fragments of magnetism preserved in magnetic minerals in the crust. Ultraviolet images of Mars at night have revealed that auroras tend to form near these crustal magnetic fields, which makes sense if magnetic fields are required for particle acceleration.
The Girazian team''s work also takes into account the solar wind conditions. They studied data from the Mars Atmosphere and Volatile EvolutioN spacecraft, which has collected ultraviolet radiation from the planet since 2014. It''s also equipped with a solar wind Ion Analyzer, which, although unsurprisingly, analyses the solar wind.
They compared information on the dynamic pressure of the solar wind as well as the strength and angle of the interplanetary magnetic field compared to ultraviolet observations on the Martian auroras. It''s been discovered that outside the crustal magnetic field areas, the dynamic pressure of the solar wind plays a crucial role in the detection frequency of auroras.
However, the pressure of the solar wind seems to play little role in the brightness of the auroras. This suggests that space weather events, such as coronal mass ejections, where masses of charged particles are ejected from the Sun and are associated with higher solar wind pressure, may trigger Martian auroras.
The orientation of the magnetic field and the solar wind appear to play a major role in the formation of auroras on Mars. At certain angles, the solar wind appears to be beneficial to magnetic reconnection events or particle acceleration required to produce the ultraviolet glow.
These findings, according to researchers, reveal new information on how interactions with the solar wind can produce auroras on a planet stripped of its global magnetic field. This information can be used to help better understand the formation of discrete auroras on very different planets.
"Now is a very fruitful and exciting time for studying aurora at Mars," Girazian said.
"The MAVEN database of discrete aurora observations is the first of its kind, which allows us to understand the basic features of the aurora for the first time."
The research has been published in the Space Physics Journal of Geophysical Research.