“Temporary but profound.”
That’s the language NASA used to describe the effect comet C/2013 A1 had on Mars during its close encounter with the planet in 2014. And thanks to NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, the space agency discovered the comet’s flyby vastly affected the planet’s magnetic field.
Launched on Nov. 18, 2013 from Cape Canaveral, Fla., the MAVEN spacecraft arrived at Mars on Sept. 21, 2014. Its mission: to collect data about Mars’ upper atmosphere, ionosphere, and determine the effects the sun and solar wind have on those planetary layers.
C/2013 A1’s encounter wasn’t unexpected. In fact, NASA had shut off some instruments aboard the MAVEN spacecraft, and other orbiters, to protect some equipment. But MAVEN’s magnetometer remained active. The magnetometer has been compared to an electric compass. Essentially, it measures the strength and direction of the planet’s magnetic field.
“The importance of studying the planet’s magnetic field is rooted in the theory that Mars lost its global magnetic field billions of years ago, allowing the solar wind to strip the atmosphere and dry out the planet,” according to NASA. “Unlike Earth’s global magnetic field, which surrounds the entire planet, Mars only has patches of magnetic field left in its crust. This can create pockets of atmosphere that are protected against solar wind and others that are left vulnerable.”
At its closest proximity to the planet, C/2013 A1, also known as Siding Spring, was separated by roughly 87,000 miles of space. Siding Spring is surrounded by its own magnetic field, which is caused by solar wind interacting with plasma from the comet’s coma. While the comet’s nucleus is about one-third of a mile, the coma—a cloud of dust particles around the comet—stretches 600,000 miles in every direction.
When the comet flew by Mars, the planet was doused with charged particles from the coma. Thus, the two magnetic fields merged, causing Mars’ magnetosphere to realign.
“With the comet’s advance, these effects built in intensity, almost making the planet’s magnetic field flap like a curtain in the wind,” according to NASA. “By the time of closest approach—when the plasma from the comet was densest—Mars’ magnetic field was in complete chaos.”
The disturbances were measurable for hours after the flyby.
NASA believes the effects of the comet’s flyby were akin to a solar storm, allowing gas to escape form the planet’s upper atmosphere.
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