NASA’s armada of Mars spacecraft all avoided damage from the comet that flew by the planet Sunday, including the Mars Reconnaissance Orbiter with its HiRISE camera managed by the University of Arizona.
Alfred McEwen, of the UA’s Lunar and Planetary Lab, said HiRISE took pictures of Comet Siding Spring before, during and after its close approach to Mars on Sunday.
He had previously described that effort as an attempt to photograph a speeding bullet from a roller coaster.
The comet is the bullet, whizzing by at 125,000 mph. The spacecraft is the roller coaster, orbiting Mars at 7,000 mph.
The mathematical calculations done to make sure the camera is pointed in the right place at the right time are all done in advance, he said.
“The hard part was predicting where the comet would be,” he said.
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The nucleus of the comet was smaller than predicted — about 500 meters in diameter — and images of it contain no more than three pixels, McEwen said.
Still, he expects his team will learn a lot from the “small and fuzzy” image of the comet and be able to define its geometry. “It’s really tough but we have multiple images,” he said Monday, as the team worked to put together an initial image for release by NASA.
“We also observed it as it approached. Its brightness showed a strong periodicity.”
The multiple images will allow the team to “make little movies and see how it changes as it rotates,” he said.
That apparent regular change in its brightness could indicate an irregular shape or reflect activity from erupting jets of gas, he said.
Comet Siding Spring is a long-period comet that originated in the Oort cloud at the distant edge of the solar system.
It was discovered in January 2013 by Robert McNaught at Siding Spring Observatory in Australia, using one of three telescopes managed by the UA’s Catalina Sky Survey.
On Sunday at 11:27 a.m. Tucson time, it passed within 86,000 miles of Mars’ surface. That’s about a third of the distance between Earth and the moon.
McEwen said he and a few other researchers came to the office Sunday morning to watch the drama unfold, even though their work had been completed long before.
“This was fun for me. A lot of fun.”
Contact reporter Tom Beal at tbeal@tucson.com or 573-4158.