Comet Flyby Sends Mars’ Magnetic Field Into Chaos

A close comet flyby sent the magnetic field of Mars into chaos, according to researchers, even blowing some of the thin atmosphere into space. The natural experiment was a rare chance to understand the Martian atmosphere, but a more immediate question might be what would happen if there was a similar flyby near Earth?

The answer, one researcher told the Denver Post, is the “the most spectacular meteor shower the Earth has ever seen.”

But Earth has an active core that generates a strong magnetic field, one that defends the planet’s atmosphere from the occasional comet flyby, among other things. Mars, on the other hand, lost its strong field about 4.2 billion years ago. It still has a weak magnetic field, but only because of a thin layer of plasma, charged particles, on the periphery of the atmosphere. That field isn’t much.

That makes a comet like Sliding Spring particularly dangerous, and NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) space probe was there to see the show.

Bruce Jakosky, MAVEN’s principal investigator from the University of Colorado’s Laboratory for Atmospheric and Space Physics, explained more in a NASA release.

“We saw a significant impact at Mars. It completely disrupted the Mars magnetosphere.”

The researchers didn’t set out to study the incident, and according to Jakosky, “had no clue” what to expect.

“This was something that had never happened before. This isn’t something we set out to study, but we took advantage of this natural experiment.”

Comet Sliding Spring has its own magnetic field. That field is generated by an interaction between solar wind and an aura of gas emanating from the comet’s center. Although the center of Sliding Spring is the size of a nugget, it manages to generate a field that stretches about 600,000 miles in all directions.

So when the comet came within 87,000 miles of Mars, that field of gas, known as a coma, swamped the Martian atmosphere for several hours, even reaching the surface.

At first the effects were barely noticeable.

MAVEN science team member Jared Espley, explained,”the main action took place during the comet’s closest approach, but the planet’s magnetosphere began to feel some effects as soon as it entered the outer edge of the comet’s coma.”

Then some parts of the magnetosphere, the magnetic environment, started to realign and point in different directions. The effects intensified, causing Mars’ magnetic field to “flap like a curtain in the wind” according to NASA. Finally, the magnetosphere fell into complete chaos.

The effects of the comet were observable for several hours after the flyby.

The scientists believe the event was similar to what happens to the Martian atmosphere in a strong solar storm. Like with solar storms, a small amount of Mars’ atmosphere was lost to space as a result. In the end, understanding those interactions is a top priority for the MAVEN mission, according to Jakosky.

“With MAVEN, we’re trying to understand how the sun and solar wind interact with Mars. By looking at how the magnetospheres of the comet and of Mars interact with each other, we’re getting a better understanding of the detailed processes that control each one.”

Observing a comet flyby putting that magnetosphere into chaos might not have been expected, but it was a welcome treat for the Mars researchers.

[Image via NASA/GSFC]