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.

This week a comet sailed past Mars closer than any known comet flyby of Earth or Mars.

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.

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

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

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 .

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

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

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.

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

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).

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.

NASA / Via mars.nasa.gov

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