Mars is all set to protect its beloved robots as comet Siding Spring charges past today spewing dust and gas during its close approach to the Red Planet. Meanwhile, everyone from the rovers to Earth-based telescopes will be tracking the comet, learning as much as possible.

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Top image: Mars protecting its robotic inhabitants. Image credit: Alex Parker

Comet Set To Graze Mars This Sunday

The comet's closest approach will be at 11:28 am Pacific Time (2:28 pm Eastern Time) on Sunday, with the planet passing through the densest particle cloud approximately 100 minutes later. The comet nucleus is just 700 meters diameter, a tiny fraction of the 4-kilometer behemoth Philae will land on next month.

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The closest approach really will be close: scientists are pinning the anticipated distance at just 139,500 kilometers from Mars, or less than a third of the Earth-Moon distance!

Comet Siding Spring will be grazing Mars at one-third the Earth-Moon distance. Image credit: NASA

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The passing distance for Comet Siding Spring is so close to Mars, it's less than proposed orbital distance for the James Webb Space Telescope around the Earth. In all of recorded history, the Earth has never been grazed that closely. Our nearest encounter was with Lexell in 1770, a comet that skipped past at six times farther away than the moon.

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Comet Siding Springs anticipated trajectory. Image credit: NASA

Just six days after Siding Spring's closest approach with Mars, the comet will reach its closest approach to the sun and begin its million-year journey back into the outer reaches of the solar system.

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Observing The Moment of Closest Approach

While you can follow along at home with a variety of science feeds, the close approach is mostly going to involve a whole lot of rather dull-looking data collection and maybe a few pixelated images, with the real excitement showing up months later after data-crunching analysis tells us more about the comet.

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NASA's planned observing activities during the close approach. Other space agencies have additional observing plans. Image credit: NASA

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In the past few months, the Mars Reconnaissance Orbiter, Mars Odyssey, Mars Express, and even the newly-arrived MAVEN and Mangalyaa satellites have been adjusting their trajectories to ensure they'll be protected by Mars during the comet's closest approach. While the comet is not expected to impact the planet, its coma and tails of dust, gas, and stray particles could sandblast delicate equipment.

The satellites will be entering "minimum risk" modes as the comet reaches closest approach, balancing between collecting data and minimizing the risk of damage to these scientifically-productive spacecraft. After the closest approach, the satellites will be checked out for any damage, and get back to imaging the planet for post-comet observations.

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Comet Siding Spring in far-infrared light as imaged by the European Space Agency's Herschel space observatory on October 17, 2014. Image credit & read more: ESA/Herschel/PACS/Cs. Kiss et al.

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Ground-based preparations for the rovers are less intense. In the past few weeks, the Opportunity and Curiosity rovers have taken test-images of the twilight sky, practicing appropriate camera settings. Now both have been photographing the comet for real this last week, and will continue to take images throughout the closest approach. Although it isn't likely since the comet warmed up early and started shedding dust a while ago, with a bit of luck, the rovers may experience a Martian meteor shower as the comet's dust burns up in the planet's thin atmosphere.

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Artist's concept of comet Siding Springs grazing past Mars in October 2014. Image credit: NASA

Scientists will be monitoring the robots during the encounter using the Deep Space Network. The Madrid complex in Spain will handle communications for the closest approach, handing off to the Goldstone complex in California during the period of maximum particle flux. Every station antenna will be pointed at Mars during the encounter for maximum redundancy.

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A Comet Discovered In Imperilled Skies

Siding Spring comet was discovered by observers at the Siding Spring Observatory in Australia in January 2013. The comet was more difficult to spot than usual because of its unusual orbit: it crosses through the ecliptic, sneaking up on us from below. This is the comet's first journey into the inner solar system since it was booted out of the Oort cloud.

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This isn't the first comet discovery from Siding Springs Observatory — they're one of most prolific comet-spotting group on the planet, second only to the LINEAR project in New Mexico. They've found so many comets that several actually bare the same name: this comet's technical designation is Siding Spring (C/2013 A1). But Siding Springs Observatory may soon be losing its dark skies if a coal mine development starts up next door, greatly hindering their observing efforts.

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Discoverers of comet Siding Springs protesting a potential coal mine development threatening their dark skies. Image courtesy of Malcolm Hartley

Mars and the comet will not be visible from Australia during closest approach, although astronomers have been using the observatory to track the lead-up to today's event.

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Comet Siding Spring and Mars the day before closest approach as seen from Siding Spring, Australia. Image credit: James Willinghan

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Satellites Heathy In Post-Approach Check-Ins

The European Space Agency's Mars Express and all three of NASA's satellites have called home with no damage reports from their close encounter with the comet.

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