Opportunity, Curiosity, but No View of Mars Sky Show By KENNETH CHANG

A series of images taken by the Mars Reconnaissance Orbiter of Comet Siding Spring as it passed near Mars on Oct. 19. Credit NASA, via Agence France-Presse

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,” Dr. Schneider said during a NASA news conference.

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,” Dr. 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. “Curiosity and Opportunity don’t take movies,” said James L. Green, director of NASA’s planetary sciences division. “They just weren’t designed to be able to do that.”

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 Dr. 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.

Dr. Schneider said that 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.

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 who is the lead investigator for the instrument.

Most of the changes in the Martian atmosphere dissipated within hours.

The NASA and E.S.A. orbiters were positioned on the opposite side of Mars when the peak of comet dust arrived. Traveling at 126,000 miles per hour, even a small particle could have damaged or destroyed a spacecraft.

Comet Siding Spring, named after the observatory in Australia where it was first identified, in January 2013, originated from the Oort Cloud, a ball of icy debris about a light-year away. Although several Oort Cloud comets fly through the inner solar system each year, by the time they are seen, there is not enough time to send a spacecraft to study them.

The comets that have been studied up close, like Halley’s Comet, are closer in and return to the inner solar system every few years or decades.

With Siding Spring and its close encounter with Mars — less than half the distance between Earth and the moon — the spacecraft were already there to conduct the first close-up observations of an Oort Cloud comet. Images taken by NASA’s Mars Reconnaissance Orbiter showed the comet’s nucleus was smaller than the expected 1.2 miles, and it was rotating once every eight hours.

Meanwhile, the European Space Agency is finishing preparations for a high-risk, high-reward attempt to place a small lander on a comet next week.

Its Rosetta spacecraft arrived at Comet 67P/Churyumov-Gerasimenko in August. On Wednesday, a 220-pound lander named Philae is to detach from Rosetta for a seven-hour descent to the surface of the 2.5-mile-wide comet, tugged down by its gravitational pull.

Once Philae is on its way, it has no way to adjust its trajectory, and the mission managers admit the attempt could go awry if the lander ends up on a boulder or in a hole. “We have to be a bit lucky,” said Andrea Accomazzo, the flight director.