| Kerry Sheridan |
WASHINGTON (AFP) – Last month, an exotic deep space comet flew by Mars and unleashed an unexpectedly strong meteor shower that briefly changed the chemistry of the Red Planet’s upper atmosphere, NASA said Friday.
The comet, Siding Spring, came from a distant region of the solar system known as the Oort Cloud.
Its rare shave past Earth’s neighbouring planet on October 19 at a speed of 35 miles (56 kilometres) per second was closely monitored by a host of human-made spacecraft.
“We believe this type of event occurs once every eight million years,” said Jim Green, director of NASA’s Planetary Science Division.
The comet released far more dust than NASA anticipated – thousands of kilogrammes by preliminary estimates – as it passed 87,000 miles from Mars.
“The comet’s dust slammed into the upper atmosphere, creating a massive and dense ionospheric layer, and literally changed the chemistry of the upper atmosphere,” Green told reporters. This additional layer of ions, in an electrically charged layer high above the planet, was temporary.
NASA said it was the first time scientists have ever connected debris from a meteor shower to such a significant change in the atmosphere.
The US space agency hopes further study will reveal if there are any long-term effects.
The resulting meteor shower likely lasted an hour or more, according to data from an orbiting NASA spacecraft called the Mars Atmosphere and Volatile Evolution Mission (MAVEN).
Its scientific instruments also detected eight different types of metal ions, including sodium, magnesium and iron, marking the first such measurements of an Oort Cloud comet, which some experts likened to a snowball in space.
MAVEN “observed intense ultraviolet emission from magnesium and iron ions high in the atmosphere in the aftermath of the meteor shower,” said the US space agency.
“Not even the most intense meteor storms on Earth have produced as strong a response as this one.” Had humans been on Mars, they might have seen a yellow glow in the sky, said Nick Schneider, instrument lead for MAVEN’s Imaging Ultraviolet Spectrograph at the University of Colorado, Boulder.
“It would have been truly stunning to the human eye.” There were “probably thousands of shooting stars per hour,” Schneider told reporters.
A layer of sodium was likely left behind, high in the Martian atmosphere, leading to a yellow afterglow, he added.
Orbiters including MAVEN, NASA’s Mars Reconnaissance Orbiter (MRO) and the European Space Agency’s Mars Express were manoeuvered to the other side of Mars to avoid the debris from the comet.