A comet that zipped past Mars last month dumped tons of dust into the planet's atmosphere, providing a spectacular light show, scientists said Friday in presenting initial scientific findings from the flyby.
Nick Schneider, a University of Colorado planetary scientist working on NASA's Maven orbiter mission, estimated that thousands of shooting stars — specks of cometary dust burning up in the atmosphere — streaked across the Martian sky that night.
"It's extremely rare in human history, and it would have been truly stunning to the human eye," Schneider said.
Highlighting the limitations of robotic explorers, neither of NASA's Martian rovers, Opportunity and Curiosity, were able to observe the shooting stars. "We've got all these high-tech robots around," Schneider said, "but I have to say, it might be the most sensitive scientific instrument of all to have a human lying outside with dark-adapted vision looking up at that sky."
Opportunity was able to snap photographs of the comet, Siding Spring, as it passed within 87,000 miles of Mars on Oct. 19. It was the first close-up observations of a comet from the Oort Cloud, a ball of icy debris about a light-year away. Orbiting spacecraft, however, vividly observed the effects of the dust. Instruments on the Maven orbiter, which fortuitously arrived weeks before the comet, looked at the upper Martian atmosphere, and afterward, a bright color of ultraviolet light associated with magnesium appeared. Other colors showed the presence of iron.
"These are not what you expect for atmospheric ingredients," said Schneider, the lead scientist for the Maven instrument that made those observations, "but they are what you expect from comet dust."
Another Maven instrument detected sodium, potassium, manganese, nickel, chromium and zinc. Schneider said magnesium is typically 10 percent by weight of comet dust, leading to an estimate of thousands of kilograms of dust showering on Mars in about an hour. If that material arrived in pieces the size of sand grains, "you can make quite a meteor shower," he said.
Most of the changes in the Martian atmosphere dissipated within hours.
A radar instrument on the European Space Agency's Mars Express orbiter observed in the atmosphere an additional layer of electrons, the result of falling dust particles burning up. "This is extremely unusual," said Donald A. Gurnett, a physics professor at the University of Iowa.
New York Times
