When comet C / 2013 A1 (Siding Spring) missed the Red Planet in October 2014, it was an unprecedented opportunity for an armadis of Martian robots to get a platform for an interplanetary spectacle. But, no matter how dazzling the spectacle may seem this demonstration flight, the real drama was not noticed by the cameras of the orbiters of Mars and the rovers. She was able to detect using a magnetometer. And this magnetometer, located 100 miles above the surface of Mars, revealed chaos.
“Comet Siding Spring has plunged the magnetic field around Mars into chaos,” said Jared Esplay of NASA's Goddart Space Flight Center in Greenbelt, Maryland and a member of NASA’s Mars atmospheric science team and Maven spacecraft in a NASA press release. “We believe that this clash blew away part of the upper layers of the atmosphere of Mars, just as if there had been a strong solar storm.”
Although the magnetic field of Mars is weak and spotty (unlike the strong and global Earth's magnetosphere), the sensitive Maven magnetometer detected a huge shock in orbit after Siding Spring invaded the magnetic field of the planet. The comet's core can only be a third of a mile wide, but the atmosphere surrounding the core (known as coma) was 600,000 miles wide when it collided with Mars. (A coma is formed by solar heating - the ice contained in the comet's core sublimates into space, pumping gas into the coma). As a result of interaction with the solar wind, comets also create their own magnetic fields, paving their way through the coma. Therefore, when Siding Spring boomed near Mars, having traveled close to a distance of 87,000 miles, the magnetism of the comet struck the weak magnetic field of Mars, leaving it in violent instability for several hours.
“The main action took place during the comet's closest approach,” said Esplay, “But the planet’s magnetosphere began to sense some effects as soon as it entered the cometary coma's outer boundary.”
These magnetic observations were very successful, since Maven had arrived in the orbit of Mars a few weeks before this close encounter. Although most of the instruments of the spacecraft were turned off at that time (in order to protect them from possible damage from comet dust), the magnetometer remained on at the time, making unique observations of how the two magnetic fields cut into each other. “Thanks to Maven, we are trying to understand how the sun and the solar wind interact with Mars,” added Bruce Jacoski, principal investigator for Maven from the University of Colorado at Boulder. “Looking at how the magnetospheres of comet and Mars interact, we get a deeper understanding of the detailed processes that control each of the objects.”
Now we know that the atmosphere of Mars is slowly seeping into space, because its magnetic field is not strong enough to fully protect it from solar wind erosion. And thanks to these observations, Maven formed the picture that this magnetic trick with “hit and run” from Siding Spring led to the fact that a piece of the atmosphere was torn off from the Red Planet. This gives a chance to understand what happens when comets and planets almost collide.
