This Sunday Earthians will witness something truly unique, estimated to happen maybe once every million years: a comet the size of a small mountain will fly by Mars, becoming the first comet to have ever come so close to Earth in recorded history.
The name of this visitor from the Oort Cloud (the Outer Solar System’s icy swarm) is Siding Spring, and it will zoom within 87,000 miles (139,500 kilometers) of Mars tomorrow (October 19) at 18:27 (GMT).
This is the comet’s first-ever pass into the inner solar system: scientists believe that, since its formation at the time the Solar System itself was born (4.6 bn years ago), it was booted out to the Oort Cloud and came no closer than the Solar System’s gas giants since then. So why has it changed its usual orbital pattern?
The most likely theory is that another large celestial body, like a passing star, changed its orbit diverting it toward the Inner Solar System. Now, this means that, never been so near to the Sun before, it’s sort of untouched – i.e, looking the same today as it did 4.6 billion years ago. Wow!
This is the first time we have the opportunity to have such a close look at a pristine Oort Cloud comet (in case you wonder, Rosetta’s target, Comet 67P/Churyumov-Gerasimenko, is instead a Kuiper Belt’s object, nearer to the Solar System. Not less interesting for this, but a different kind of animal).
Unsurprisingly, NASA is well prepared for the encounter – with a plethora of devices ready to capture all possible data, together with some beautiful images.
There are other interesting aspects to observe in this spectacular event, not simply studying the comet but also observe any notable effects its particles have on the planet’s thin atmosphere.
As it is often the case, good opportunities come with a price, and in the case of this event is the risk of having Mars’ orbiting spacecrafts (from NASA, Europe and India) damaged by the high-velocity dust particles coming off the comet.
NASA Mars rovers Opportunity and Curiosity, being on the ground, are relatively safe, since the atmosphere of Mars, though thinner that Earth’s, will shield them from the dust. Both rovers will point to the comet and make observations.
A curiosity: the comet C/2013 A1 has been given the moniker “Siding Spring” after the observatory where it was discovered in 2013, the Siding Spring Observatory in New South Wales, Australia.