It was a close encounter of the comet kind. A, coming into relatively close proximity with NASA's three orbiters there: Mars Odyssey, Mars Reconnaissance Orbiter and Mars Atmosphere and Volatile Evolution (MAVEN) orbiter. NASA was concerned about the release of dust from the comet, which could potentially gum up the parts on the orbiters.
In a preemptive move, NASA ordered the orbiters to hide behind Mars for a cosmic game of hide and seek to minimize exposure to particles. "The comet sped past Mars today much closer than any other know comet flyby of a planet," NASA reported Sunday. It came within 88,000 miles of Mars. All three orbiters checked back in with headquarters after the flyby to report themselves as healthy.
The comet, known as C/2013 A1 Siding Spring, gave NASA a rare opportunity to study a comet in fairly close quarters using the orbiters. Odyssey, for example, took images of the comet using its Thermal Emission Imaging System. Those images are being downlinked to Earth for processing and study. Odyssey was also tasked with studying how the comet's dust and gas emissions might impact Mars' atmosphere.
The Mars Reconnaissance Orbiter spent half an hour hiding behind the Red Planet to avoid the comet's high-velocity dust particles, but that didn't stop it from making some planned observations. Like Odyssey, it is also looking at whether the comet's tail interacted with Mars' atmosphere as it swooped by.
MAVEN, the newest orbiter to arrive at Mars, is in the earliest phases of its mission, but NASA still took the opportunity to collect data on the comet. Scientists are hoping to learn more about the composition of the gases and dust released by the comet thanks to information gathered by MAVEN's onboard instruments.
The duck-and-cover maneuvers ended up being effective for protecting the orbiters. It could take days to download all the data. After that, researchers will have a lot of information to process. "This comet is making its first visit this close to the sun from the outer solar system's Oort Cloud, so the concerted campaign of observations may yield fresh clues to our solar system's earliest days more than 4 billion years ago," NASA said.