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A Giant Comet Passed By Mars Closer Than The Moon Is To Earth

Are we out of the woods yet? Here's why the once-in-a-lifetime event is a big deal.

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On Oct. 19 a comet sailed past Mars closer than any known comet flyby of Earth or Mars.

NASA/JPL-Caltech / Via mars.nasa.gov

It sailed by at a distance of approximately 87,000 miles, according to NASA, and won't be back for more than a million years.

Named Siding Spring, the comet is shown here in a composite that NASA released, taken using the Hubble Space Telescope.

NASA, ESA, PSI, JHU / APL, STScI/AURA

Comets are sometimes called “dirty snowballs” because they are a collection of debris and ices. Since it's not the only comet named Siding Spring, it uses the official tag, C/2013 A1.

Scottish-Australian scientist Robert H. McNaught found the comet, which is named after the observatory where it was spotted. The Siding Spring Survey, the early-warning program that discovered it, was shuttered last year after it lost its funding, according to The Guardian.

The comet skirted by at about one-third of the distance between Earth and the moon.

NASA/JPL-Caltech / Via mars.nasa.gov

Just to give you a sense of how much of a near-miss the near-miss was. Earth's closest encounter in recorded history, a comet named Lexell, was about six times the distance of the moon. It was discovered in 1770 but hasn’t been seen since.

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The flyby spurred NASA to have its Mars orbiters duck behind the planet to save them from dust particles estimated to be traveling 125,000 mph (56 km/sec).

NASA / Via mars.nasa.gov

They are happy to report that the satellites are in good health.

Siding Spring's close encounter with the sun, which occurs six days after passing Mars, could still make it risky for Mars spacecraft. The closer it gets to the star, the more the comet's tail grows as the water vapor comes off of the nucleus — and potentially chucking high-velocity particles at the spacecraft.

OK, but where did it come from?

designsstock/designsstock

Siding Spring took a million-year jaunt over to our neck of the woods. The comet spent its time canoodling with other comets in what is called the Oort Cloud.

In simplest terms: The Oort Cloud surrounds our solar system with a whole lotta icy leftover junk from when the solar system formed about 4.6 billion years ago.

The sun doesn’t have any physical or gravitational effect on the Oort Cloud, which is considered to be the “edge” of our solar system. But occasionally something disrupts one of the billions of comets’ orbit, and that’s when it makes its lonely journey into our neighborhood.

Why should I care?

NASA/JPL-Caltech / Via mars.nasa.gov

Long-period comets like Siding Spring are unpredictable, so being able to track their composition and trajectories lets us monitor future near-Earth objects even better.

On a bigger scale: As the closest flyby ever, the big guy gives scientists a closer look at our universe's origins. Cometary collisions are suspected to have brought some of Earth's earliest building blocks, like water and carbon-based molecules, according to NASA's Near Earth Object Program.

And you can rest easy: The program assures that "a catastrophic cometary collision with the Earth is only likely to happen at several million year intervals on average."

Also, it's just really fucking cool.

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