A NASA spacecraft in orbit around Mars has detected two mysterious phenomena above the Red Planet: a dust cloud scientists say shouldn't be there and an aurora reaching deep into the planet's atmosphere.

A cloud of dust at an altitude of 90 miles up to almost 200 miles is something scientists say they had not predicted.

"We saw something that we were not expecting," reported Laila Andersson of the Laboratory for Atmospherics and Space Physics at the University of Colorado in Boulder.

She presented the finding at a meeting of the Lunar and Planetary Science Conference in Houston.

"If the dust originates from the atmosphere, this suggests we are missing some fundamental process in the Martian atmosphere," she says.

Other possibilities include dust originating from Phobos and Deimos — the two moons of Mars — or carried by the solar wind away from the sun, or debris from comets, although the scientists acknowledge there's no known processes on the Red Planet that can explain the existence of dust from any of those sources in the observed locations.

NASA's Mars Atmosphere and Volatile Evolution spacecraft (MAVEN) detected the dust cloud, which has been present since the spacecraft orbited Mars in September 2014 and began operations, scientists said.

Scientists said they also discovered another Mars puzzle to consider, as a spectrographic instrument on MAVEN detected a bright ultraviolet aural glow spanning the northern hemisphere of the planet.

Auroras on Earth, known as the Southern or Northern Lights, are the result of energetic particles like electrons carried by the solar wind raining down and causing atmospheric gases to glow.

The Martian aurora, which scientists have dubbed "Christmas lights," are behaving in a manner not seen on Earth.

"What's especially surprising about the aurora we saw is how deep in the atmosphere it occurs — much deeper than at Earth or elsewhere on Mars," says Arnaud Stiepen, a member of the ultraviolet instrument team at the University of Colorado. "The electrons producing it must be really energetic."

Both observations, although mysterious, are evidence MAVEN's scientific instruments are working as intended, researchers say.

"The MAVEN science instruments all are performing nominally, and the data coming out of the mission are excellent," says Bruce Jakosky, who is the mission's principal investigator at the University of Colorado.

In terms of the dust cloud, although its source and composition are presently unknown, it does not represent a hazard to MAVEN or any of the other spacecraft orbiting Mars, NASA says.