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Spacecraft emerge unscathed as Comet Siding Spring grazes Mars

Jenny Winder, News Writer
Oct 20, 2014, 14:55 UTC, Updated Oct 20, 2014, 16:48 UTC

Sen—A first-time visiting comet from beyond the Solar System made its long-awaited close encounter with Mars yesterday as space scientists watched with fascination and trepidation.

There had been some fears for their international fleet of orbiting spacecraft from any dust in the atmospheric shroud surrounding the comet, labelled C/2013 A1 (Siding Spring).

But NASA and ESA reported that the probes around the Red Planet emerged unscathed from the flyby, which brought Comet Siding Spring to a distance of less than 139,500 km (86,500 miles) from the centre of Mars.

Instead, the orbiters, plus rovers Opportunity and Curiosity on the ground, made observations of the comet and its surrounding coma or watched for any meteors in the martian atmosphere. Opportunity sent back a photo of the comet shining brightly at magnitude -6 in its sky.

Meanwhile, Earthbound astronomers with powerful equipment enjoyed front row seats of the rare encounter, including SEN's Damian Peach, whose image of the comet approaching brilliant Mars was picked as NASA Astronomy Picture of the Day (APOD).


The comet is the fuzzy object at the centre of this picture, a raw image taken by Mars rover Opportunity. Image credit: NASA

Comet Siding Spring, discovered in January 2013, is about 700 metres in diameter and passed Mars at 56 km/s, closing to within 139 500 km at 18:27 UT on Sunday 19 October. The comet skimmed past at a little more than a third of the Moon’s distance from Earth and less than one-tenth the distance of any known comet flyby of Earth. 

Space agencies had manoeuvred their orbiters to the far side of the planet to shield them from the impact of gas and dust as Mars passed through the "fluence", the densest part of the tail and coma, about 90 minutes after closest approach, while preserving opportunities to gather valuable scientific data. 

There are currently five orbiters around the Red Planet: ESA's Mars Express; NASA's Mars Reconnaissance Orbiter (MRO) Mars Odyssey and MAVEN and India's Mars Orbiter Mission (MOM) named Mangalyaan. The close flyby presented an invaluable opportunity for science, including close-up observations of this enigmatic comet, the Mars atmosphere under the direct influence of the comet’s gas and dust, and the complex three-way interaction between Mars, the comet and the solar wind. 

“Most interestingly, we may also obtain images of cometary particles—meteors—burning up in the martian atmosphere, allowing an in-depth comparison of meteor science between Earth and Mars,” notes Håkan Svedhem, project scientist for ESA's Mars Express, before the encounter.

Mars Odyssey, the longest-lived robot ever sent to Mars came through its latest challenge in good health, reporting home on schedule. “The telemetry received from Odyssey this afternoon confirms not only that the spacecraft is in fine health but also that it conducted the planned observations of comet Siding Spring within hours of the comet’s closest approach to Mars,” said Odyssey Mission Manager Chris Potts of NASA’s Jet Propulsion Laboratory (JPL).


Comet Siding Spring planned science observations. Image credit: NASA

MRO, which has sent home more data about Mars than all other missions combined, continues operating in good health. "The spacecraft performed flawlessly throughout the comet flyby," said Mars Reconnaissance Orbiter Project Manager Dan Johnston, also of JPL. "It manoeuvered for the planned observations of the comet and emerged unscathed." 

NASA's newest orbiter at Mars, MAVEN, has also reported back "We're glad the spacecraft came through, we're excited to complete our observations of how the comet affects Mars, and we're eager to get to our primary science phase," said MAVEN Principal Investigator Bruce Jakosky of the University of Colorado.

NASA's MAVEN has already captured data from Mars' atmosphere over the last few days and will do more observations from now on to provide data before and after the brush with Siding Spring.

Downlink of data from the orbiters has begun but may take some days to complete.

Siding Spring spent most of its life in the Oort Cloud that surrounds the Solar System, lying some 5000–100 000 times the Earth–Sun distance and containing billions of comets. It is the first Oort Cloud comet to be studied up close by spacecraft, giving scientists an invaluable opportunity to learn more about the materials, including water and carbon compounds, that existed during the formation of the Solar System 4.6 billion years ago.

NASA's Mars rovers Opportunity and Curiosity were also watching the comet from the surface of Mars. Space observatories, Hubble, Kepler, Swift, Spitzer and Chandra, the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) and two Sun-watching spacecraft, Solar TErrestrial RElations Observatory (STEREO) and Solar and Heliophysics Observatory (SOHO) tracked the event as did the ground-based Infrared Telescope Facility on Mauna Kea, Hawaii.

NASA hosted a news briefing to outline the space and Earth-based assets that will study the comet at Mars. Credit: NASA Jet Propulsion Laboratory