Since February’s close approach of asteroid DA14, I’ve spent a lot of time on my home-made solar system simulation model, mostly modelling rock clouds.
Last week Marvin mentioned comet Ison. So I got hold of C2012S1 Ison‘s state vectors (barycentric position and velocity), and took a look at what it was doing. It’s a sun-grazing comet, and is (or was) expected to be one of the brightest comets for a long time. Right now it’s inbound, and is lying just beyond Mars. It’s due to reach perihelion on 28 Nov 2013, before heading back out again, passing beyond the orbit of the Earth on 29 December.
There seems to be an incredible amount of nonsense on the internet about Ison. But it’s not going to hit Mars or Earth or anything else. It comes quite near Mars on 1 October, but is several million kilometres above the ecliptic (the plane in which the planets circle) at that point in time.
I read somewhere that the Earth was due to pass near its tail on about 15 Jan 2014. And according to my model it does indeed seem that the Earth will come quite near (3.5 million km) the inbound orbital path of Ison on that date.
Since Ison comes very close to the sun, there’s quite a lot of speculation about whether it will survive perihelion. I think that’s because either the sun’s radiation will vapourise it, or tidal forces tear it apart. So I took a look at what Ison would do if it exploded (left), and found that there was a small chance that a few fragments would strike the Earth on their way out from the sun. If they did, I reckoned it would be between about 29 Dec 2013 and 15 Jan 2014. And they would probably be particles of ice rather than rocks, in orbits that take them slightly beyond the Earth before they fall back towards the sun.
And I came across another comet, C2013A1 Siding Spring, which comes very near Mars on 19 October 2014 (right). So near, in fact, that Mars will pass through the coma surrounding the icy nucleus, which could make for some excitement a year from now, since there are several vehicles on Mars and satellites around it.
Both Ison and Siding Spring are inclined at considerable angles to the ecliptic. So they don’t linger very long in the planetary ecliptic plane. Below is a view looking along the ecliptic plane, showing the paths of both comets above and below it.
In the process of reading all the speculation about Ison, I came across Dr James McCanney. He seems to be some sort of renegade physicist who believes that comet tails don’t brighten because they reflect sunlight, but because the sun discharges a current through them, lighting them up like flourescent tubes.
I’d never heard of him before, and I can’t comment on the idea. But he believes that as Ison nears Mars on 1 October, there may be an electrical discharge from it to Mars. And a similar thing might happen on about 5 Jan 2014 when Ison, Jupiter, Earth, Moon, and Venus are all lined up (and indeed they are). So the Plasma Discharge Theory of comets looks like it may soon be tested.
Anyway, one good thing about having my own simulation model is that I can check things out for myself, and draw my own conclusions, and not have to rely on NASA or the media or anyone else.