Named for the Siding Spring observatory in Australia, although officially known as C/2013 A1, Siding Spring is due to come extremely close to Mars giving our spacecraft a front row seat to viewing the spectacular. What is so different about this particular comet? Hurtling through space at speeds in the neighborhood of 126,000 miles per hour, Siding Springs comes straight from the Oort Cloud. As it is heading toward the Sun and having never before entered the inner solar system, it will be releasing gases & objects that are primordial in nature and have been frozen for billions of years. Think of it – the journey has been a long one for Siding Springs and when it passes Mars it will be far from over.
Siding Springs will pass Mars on Octobe19th at 18:28 UTC. But Rosetta will be sending Philae to land on a comet, no? Well yes, but Comet 67P/Churyumov–Gerasimenko is a comet with a current orbital period of 6.45 years making it a short-period comet AND it is believed to have originated in the Kuiper belt (as opposed to the Oort cloud). Rosetta’s comet will come closest to the Sun on August 13th, 2015.
A program scientist at NASA, Kelly Fast, had this to say of the event: "Normally you send spacecraft to comets. Here, the comet is coming to our spacecraft." NASA will be utilizing a grand armada. 3 Mars orbiters, 2 Mars rovers plus telescopes both in space and on earth will be tasked with checking the comet out. Here on Earth October 20thshould see the release of the first images taken – per NASA.
Granted odds of an impact with Mars although once upon a time anticipated now are slim; 1 in 1250 in March 2013, later 1 in 2000 and finally 1 in 120,000 – but based on preliminary size estimates the energy of such a hit would be ~20 billion megatons. Still, just the fly-by should be a thing of wonder.
A cool fact – the tail or coma of Siding Springs extends for a distance equal to that between the Earth and the Sun. That should be an amazing thing to watch and the scientific fodder gleaned during the event should be tremendous.