Remember Comet Siding Spring? In October 2014, the comet soared past Mars at about 87,000 miles away. Space agencies with orbiters around the planet reoriented them to protect against the flyby.

NASA’s MAVEN spacecraft had just arrived and was shifted to a safe area. While most instruments were turned off during the close encounter with the comet, MAVEN’s magnetometer stayed on. It wasn’t going to miss the show. Scientists couldn’t pass up such a unique opportunity to see how Comet Siding Spring interacted with Mars.

And the encounter didn’t disappoint. “Comet Siding Spring plunged the magnetic field around Mars into chaos,” said Jared Espley, a MAVEN science team member. “We think the encounter blew away part of Mars’ upper atmosphere, much like a strong solar wind would.”

Did you know: Comet Siding Spring also has a magnetic field. It’s created as solar wind interacts with the plasma created in the comet’s coma. That’s the gas flowing from the comet’s nucleus as the sun heats it up. Siding Spring’s nucleus is only about half a kilometer wide, but its coma is much larger. Estimates indicate it stretches for more than 600,000 miles in every direction.

Mars Siding Spring comet

Because the comet passed within around 87,000 miles of Mars, the coma was easily within reach of the red planet. The coma, and the comet’s magnetic field, washed over Mars during the closest approach. For a time, it merged and then overtook the planet’s weaker magnetic field.

“The main action took place during the comet’s closest approach,” explains Espley, “but the planet’s magnetosphere began to feel some effects as soon as it entered the outer edge of the comet’s coma.”

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Here’s what happened. As Comet Siding Spring cruised towards Mars, areas of the planet’s magnetic field began to realign in different directions. This effect continued to build and NASA describes the planet’s magnetic field flapping “like a curtain in the wind.” At closest approach, it was “chaos.”

And the effects of Comet Siding Spring’s approach were measured hours after it zoomed past.

MAVEN’s primary mission is to study the effects the sun and solar wind have on Mars. With Comet Siding Spring, MAVEN’s science team witnessed an event akin to a short-lived solar storm. Scientists believe there was a brief increase of gas escaping from Mars’ upper atmosphere following the encounter.

Over Mars’ history, its weakened magnetic field leaked any potential life-supporting atmosphere away.

MAVEN sees Phobos

A couple of weeks ago, NASA released a new image of Phobos. Back in November and December, MAVEN’s orbit took it close to Mars’ mysterious moon. Here’s a look at Phobos in ultraviolet. The yellows and oranges show sunlight reflecting from the surface of the moon.

MAVEN and Phobos

Scientists will use the images to hopefully understand more about Phobos. Is it an asteroid? Or, did the moon form in orbit around Mars? That’s the question, and the data captured by MAVEN’s close encounter could help answer it.

Image credit: NASA

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