Nasa has uncovered that Mars' atmosphere contains metal ions. Nasa's Maven spacecraft, which has been exploring the Martian upper atmosphere to figure out how the planet lost most of its air, made the discovery. The metal atoms could help unearth "previously invisible activity" in the Red Planet's upper atmosphere (ionosphere).

According to Nasa, the metal particles in Mars' atmosphere come from a "constant" and "high-speed" rain of tiny meteoroids that vaporise when they hit the Martian atmosphere. The metal atoms are then transformed into electrically charged atoms after some of their electrons are torn away by other charged particles in the ionosphere.

"Maven has made the first direct detection of the permanent presence of metal ions in the ionosphere of a planet other than Earth," said Joseph Grebowsky of Nasa's Goddard Space Flight Center in Greenbelt, Maryland. Grebowsky is lead author of a research paper on Mars' unique ionosphere, which has been published in Geophysical Research Letters.

"Because metallic ions have long lifetimes and are transported far from their region of origin by neutral winds and electric fields, they can be used to infer motion in the ionosphere, similar to the way we use a lofted leaf to reveal which way the wind is blowing," Grebowsky added.

However, Mars is not alone in playing host to metal ions. They have also been detected high above the Earth's atmosphere. According to Nasa, there is "indirect evidence" that suggests that metal ions exist above other planets in our very own solar system.

"However, long-term direct detection of the metal ions by Maven is the first conclusive evidence that these ions exist on another planet and that they are a permanent feature there," Nasa said in a statement.

Nasa scientists also discovered that the metal ions on Mars behave differently than those on Earth. Metal ions on Earth are divided into layers thanks to the Earth's global magnetic field and ionospheric winds. However, Mars only has local magnetic fields that are fossilised in particular regions. It is only in these areas that the metal ions were found in layers. "Elsewhere, the metal ion distributions are totally unlike those observed at Earth," said Grebowsky.

The discovery can also help shed light on whether metal ions could contribute in any way to the "formation or behaviour" of high-altitude clouds. Further understanding of meteoric ions and their varying behaviour on Earth and Mars may also help predict the consequences of the impact of interplanetary dust in the atmospheres of other, so far unexplored solar systems.

"Observing metal ions on another planet gives us something to compare and contrast with Earth to understand the ionosphere and atmospheric chemistry better," said Grebowsky.