The close encounter between a comet and Mars has given new insight into how the planet’s environment is affected by the comets strong magnetic field.
The comet, called C/2013 A1 (Comet Siding Spring), had passed Mars in October 2014, flooding it with an invisible tide of charged particles. The comets magnetic field had temporarily merged with, and then completely overwhelmed, Mars’ weaker magnetic field.
It was only weeks before the encounter that NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft had entered into an orbit around the Red Planet. In order to protect the sensitive equipment aboard MAVEN, some instruments had been turned off during the comets flyby.
However, there were a few instruments scientists left on, one of which was MAVEN’s magnetometer. This gave researchers a front-row seat during the comet’s extraordinarily close flyby. In this first-of-a-kind observation, scientists were able view just how much mayhem the comet inflicted on the magnetic environment, or magnetosphere, around Mars as it passed.
Although the effect may have been only temporary, it was still quite profound. Jared Espley, a MAVEN science team member at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said:
“Comet Siding Spring plunged the magnetic field around Mars into chaos. We think the encounter blew away part of Mars’ upper atmosphere, much like a strong solar storm would.”
Mars does not have a strong magnetosphere generated within the planet, therefore, it is not shielded like Earth is. However, the atmosphere does offer some protection, by redirecting the solar wind around the planet, similar to how a rock diverts the flow of water in a creek.
According to NASA:
“This happens because at very high altitudes Mars’ atmosphere is made up of plasma — a layer of electrically charged particles and gas molecules.
“Charged particles in the solar wind interact with this plasma, and the mingling and moving around of all these charges produces currents.
“Just like currents in simple electrical circuits, these moving charges induce a magnetic field, which, in Mars’ case, is quite weak.”
Watch this video from NASA Goddard to find out why a magnetosphere is so important:
Comet Siding Spring
Because solar winds interact with the plasma generated in the coma (the envelope of gas flowing from a comet’s nucleus as it is heated by the sun) the comet is also surrounded by a magnetic field.
The nucleus of comet Siding Spring, the piece of ice and rock which is no more than about one-third of a mile (half a kilometer) is small. However, the coma is extensive, extending out to more than 600,000 miles (a million kilometers) in all directions.
The densest part of the coma (the inner region near the nucleus) is what’s visible to telescopes and cameras seen as a big fuzzy ball.
When the comet passed Mars, the two bodies were within about 87,000 miles (roughly 140,000 kilometers) of each other. With the comet’s coma washing over the planet for several hours, the dense inner coma may have even reached the surface of Mars.
It was during this time Mars was flooded with charged particles from the coma. The comets own powerful magnetic field then temporarily overwhelmed the planet’s own weaker one. Espley explained in a statement:
“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.”
To begin with, the changes were subtle; however when Mars’ magnetosphere (normally draped neatly over the planet) started to respond to the comet’s approach, some of its regions began to rearrange, pointing in different directions.
As the comet advanced, the effects built in strength, “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. Even hours after the comet’s departure, some disruption continued to be measured.”
Espley and colleagues believe that the effects of the plasma tide would be comparable to that of a strong, but short-lived, solar storm. Therefore like a solar storm, the comet most likely would have driven a short-term surge in the amount of gas escaping from Mars’ upper atmosphere.
Bruce Jakosky, MAVEN’s principal investigator from the University of Colorado’s Laboratory for Atmospheric and Space Physics in Boulder, said:
“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.”
Watch this briefing from NASA about Solar Wind Striping the Martian Atmosphere: