With the let-down of the much anticipated Comet ISON you could be feeling that you have had your quota of comets for a while, but within one year of comet ISON’s sad demise, we are to be visited by another comet, Comet Siding Spring. Unlike ISON it has not been potentially be the “comet of the century! Instead speculation over how bright Siding Spring will become has been left in the air with no one able to guess whether or not it will light up the sky or not. But Comet Siding Spring has caused much excitement but also a lot of worry amongst astronomers all over the world, from NASA to the Indian Space Research Organisation! So here are the facts about Comet Siding Spring to hopefully get you excited and ease any fears you may have about this curious comet.
1 – Comets have the strangest names!
The name alone is quite strange but in sticking with many naming traditions with comets it shares its name with the place or person who discovered it. In this case Comet Siding Spring is nick-named after the Siding Spring Observatory, in New South Wales, Australia; it’s officially called C/2013A1. They discovered it on 3 January 2013, making it the first long period comet discovered in 2013 by Robert H. McNaught who has so far discovered 74 comets so this isn’t new to him. He discovered it in the lesser known constellation of Lepus (the Hare), as it was flying inwards just beyond the orbit of Jupiter.
2 – The comet will NOT hit Mars!
No, it’s not going to be a case of Russian roulette with every planet standing a chance of being hit. Originally it was believed there was a small chance it would hit the planet Mars and but with more research and observation we know the comet will fly by Mars without hitting the planet. Odds of 1 in 120,000 is very low risk, but people do read odds differently! There is NO CHANCE AT ALL that this comet will hit Earth. If the comet was gong to hit Mars there is NO CHANCE AT ALL that debris from the collision could fall on Earth. There is NO CHANCE AT ALL that this comet will cause a disaster on our planet. Anyone who tells you that it will (even if they claim it is predicted in the Bible) is telling, deliberately or not, an untruth.
3 – Mars will be left eating Siding Springs dust!
It is certain that comet Siding Spring will get very close to Mars, in fact ten times closer than any comet has come in recorded history when passing the Earth. At its closest approach to Mars it will be roughly 86 000 miles from the rusty Red Planet’s surface. To put that in perspective, the Earth’s Moon is roughly 238 857 miles away from us. That’s like having the Moon nearly three times closer to us! This provides a problem depending on how active Comet Siding Spring will become, especially during its closest approach to Mars on 19 October 2014. Comet nuclei shed dust and ice as they get closer to the Sun forming a temporary and vanishingly thin atmosphere. They call this the coma of the comet, and the more dust and ice shed, the more problems there could be for the rovers and orbiters on Mars because it is believed the coma may envelop the whole planet. Orbiters especially are at risk as they are outside the atmosphere of Mars. Even though the atmosphere of Mars is thin, it will provide some protection for the rovers on the surface.
The speed of Siding Spring varies but it is estimated to be travelling at 126,000mph when it is at its closest approach to Mars, so that is a lot of fast moving particles that could hit the orbiters and damage or even destroy them (spacecraft have indeed been damaged by materials shed by comets; ESA;s Giotto came a cropper near Comet Halley in 1986). The official risk level will not be known for months with more observation needed, in particular the months of April and May will be a key time to view how active it will become as this a period when the comet will be crossing a range of distances that can see water ice on a comet becoming active. But precautions are in place as space agencies are forming back up plans to have orbiters to relocate around the planet to less active and safer areas due the peak of activity as well as repositioning them so the less important side of the satellite faces the more active area, therefore mitigating damage.
4 – Martian Rovers and Orbiters are also excited about this long distance visitor.
As we have noted, this extremely close approach of Comet Siding Spring to Mars is causing a lot of worry and panic, it has also got many astronomers excited! These camera-shy objects are masters of eluding the close up picture. When scientists and astronomers try to get spacecraft close to get a picture of an active comet’s nucleus the probe could be destroyed by the stream of material ejecting from the comet. They truly are ‘shrouded’ in mystery. So this close approach is very exciting because we may be able to get some of the closest pictures of a comet’s nucleus than ever before. But this means pushing the luck of the rovers and orbiters by keeping them as close as possible for as long as possible to get the shots, which could result in damaged or destroyed Martian rovers and orbiters. So fingers crossed we can get some never before seen pictures of the nucleus of comet Siding Spring.
5 – It has taken its time getting here!
Astronomers have estimated that has taken millions of years for it to travel in from the Oort Cloud which extends nearly one light year away from the Sun. It has been on a one million year journey to the centre of the Solar System and it will be another one million years before it comes back. So I would definitely get out the binoculars!
6 – Blink and you will miss it!
For taking such a long time to get to the centre of the solar system it isn’t going to take it’s time to look around when it gets here. As stated before, it will be travelling at approximately 126,000mph and unlike comet ISON it doesn’t plan on sticking around. After its closest approach to Mars on 19 October, it will take it just six days to reach its closest approach to Mars so it will not provide the Earth a beautiful night sky object to view. There may be a chance for those in the southern hemisphere to see it through a telescope or even a pair of binoculars from the middle of September onwards, but how active it will be and how visible it will become relies on how it reacts getting closer to the Sun in the next few months.
7 – It is very tiny!
There have been estimates put forward about how big the nucleus of Siding Spring is and their range was originally very big. Astronomers believed it could be anywhere between 8 km to 50 km wide! If it is the latter and it collided with Mars the impact could yield 20 billion megatons (that means it would explode releasing as much energy as 20 milion million million tonnes of TNT)! That is of course a hypothetical impact; remember it is not going to occur. Current estimates suggest the nucleus is about 700 m wide, far smaller than that of Comet 67P/Churyumov–Gerasimenko (target of ESA’s Rosetta mission) which is about 4km wide.
8 – Comets have come this close to planets before!
This is not the first time a comet has got close to a planet, it has happened before but the story did not end too well for said comet. You may remember comet Shoemaker-Levy 9 that broke apart and collided with Jupiter in July 1994. This was a first in modern times where we could actually record the collision with the huge gas giant. Needless to say a collision with the ‘rocky midget’ Mars would be much more dramatic and be likened more to a massive explosion of dust and debris rather than a huge giant just swallowing some rocks! See below for a video of the collision.
After the let-down of Comet ISON it is understandable why the same hype has not been pushed onto comet Siding Spring. People are being much more cautious about blowing the comet’s trumpet but fingers crossed that we can at least get some of the closest images of a comet when it passes Mars. Needless to say we will probably be hearing lots more about the progress of Siding spring over the following few months when we should get a more accurate idea of how active it’s going to become.
(Article by Kerry Scullion, Education Support Officer)
(Updated by Colin Johnston, 9 October 2014)