Monday, 23 September 2013

A newbies guide to Ison part 3

How fast is Ison?

Ison is moving fast! As of September she is traveling at approximately 107826 kph (67,000 mph), at this speed it would take Ison just 10 seconds to travel the entire length of the M1 motorway! 
But that's not the whole story, Ison is accelerating. As the comet gets closer to the sun, the effect of the suns gravity is stronger and will cause Ison to speed up. In December when Ison reaches the sun, the sun will "slingshot" her back out into the solar system at tremendous speed. Remember when you were a kid running up to a lamp post, grabbing hold of it and being swung round? Remember how you suddenly speed up, well swap the lamppost for the sun and you for Ison! (If you don't remember doing it, go and have a go now!)
When Ison goes through this slingshot around the sun we expect her to reach speeds of up to 1,359,895 kph (845,000 mph)! At this speed the M1 would take just 0.8 seconds, it is rumoured that Jeremy Clarkson has been seen building a giant harpoon to try and capture Ison.......

Where did Ison come from?

We believe Ison came from the Oort cloud. Our solar system sits inside a large ball shaped cloud of ice and rocks. This is the Oort cloud and is generally considered to be the boundary of the solar system and the birth place of most comets. 

You may notice on the picture above that the cloud has two parts, the inner cloud and the outer cloud. Imagine a football with a dinner plate inside. The outer cloud is where we think Ison came from. The Oort cloud contains trillions of frozen objects, mainly water, ammonia and methane.
The edge of the Oort cloud is about one light year away from the sun, around 22,5000,000,000,000 km (13,950,000,000,000 miles) and at this distance the effect of the suns gravity is very weak. It’s thought that the gravitational effect from our neighbouring stars dislodge chunks of ice and push them in to our solar system where they become comets, like Ison. Very little is known about the Oort cloud in fact most of it is theory, we have yet to send a space probe there! 

What is Ison's mass?
Just like size, it's not easy to work out the mass of comets! Many astronomers are reluctant to even take a guess, but we will! We have estimated Ison to be 3,175,146,590 kg. This estimate was reached by a mean average of estimates from 11 BCRS members. All the estimates were within a 9% range, so we are quietly confident with its accuracy. That said, new data is coming in daily so we might revise this figure in the future, but we would be surprised if it was by much! 

How close to earth will Ison get?
At its closest point Ison will be 69,000,000 km (39,900,000 miles) from earth on the 26th of December.

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