The comet's projected orbit, calculated about a month after its discovery, indicated that it would make an exceptionally close approach to Mars – within a hundred thousand kilometers. This occurrence was truly extraordinary and unparalleled, as no comet in recent history has ever come so close to Earth.
On October 19, 2014, Siding Spring made its historic pass by Mars, coming as near as 146,000 kilometers from the planet. During this time, it's estimated that the comet appeared as a -6 apparent magnitude from the Martian surface, making it the second-brightest object in the sky after the Sun.
Scientists eagerly directed all orbiting and surface probes towards the comet to study this once-in-a-lifetime event. As the comet neared Mars, the probes detected a high-intensity shower of cometary dust, comprised of elements such as magnesium, iron, potassium, and more.
Further observations allowed for estimations of the comet's size and rotation period. The Siding Spring Comet's diameter was measured to be between 400 and 700 meters – smaller than initially thought – and its rotation period was determined to be eight hours.
Moreover, during the closest approach, some probes were able to examine the intricate interaction between Mars' weak magnetic field and the comet's own magnetic field, generated through its interaction with solar wind.
Credit: SEN/Damian Peach.
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