Comet ISON - Sixty Symbols

I'm going to talk about comments today specifically a comment that is on its way into the inner solar system and may well treat us to quite a spectacular sight in a few weeks time now we have no idea what's going to happen to this comment but we know a few things about it that indicate that it might well put on quite a show it's called comet Ison and it's from a long way away it is a kind of comet that his never ever been in our solar system before and it never ever will be again it's a one time visitor and not only that but it's going to pass very very close to the Sun it's called a sungrazing comet and those two facts together make it quite interesting comets can orbit the Sun just like the planets do but they tend to orbit it in a different way so I can I can make a little model in the solar system here got got our Sun this is absolutely not to scale if most of the planets orbit in a plane and they tend to have orbits that are technically ellipses those orbits are governed by Kepler's laws of orbital dynamics which are very well known have been known for hundreds of years but comets tend to do something very different so instead of a slightly squashed circle they can have orbits that are very very elliptical sort of the shape of this whole table and they don't have to be located in the plane of the ecliptic the same plane that all of those planets do they can be tilted up at quite high angles they can be oriented in all sorts of different directions they can have orbits that take only a few years or a few tens of years to go around the Sun they kind of orbits that take tens of thousands of years and they get flung way out into the outer solar system and beyond and then back in again this special kind of comet is visiting us from the Oort cloud the Oort cloud is probably the source of a lot of these very distant orbiting comments and it's probably we think a remnant of a leftover bit of when the solar system formed from a big disk of debris and material that got puffed up and sent out got sent out so far that is actually we think probably billions of tiny little icy objects in a cloud about a Lightyear in radius that's a quarter of the distance away from the next nearest star that's way way beyond where the actual planets orbit those objects probably stay out there millions and millions of years but they're very vulnerable to being perturbed and bumped around a bit so a passing star or the gravitational field of the Milky Way might have nudged one just enough that it it left the Oort cloud and it is plunged all the way into the inner solar system but it's not on an elliptical orbit it's not this close squashed circle it's on a hyperbolic orbit it's following a hyperbola that will take it in towards the Sun whip it round the Sun in a sort of slingshot manner this is exactly the kind of orbit that we send spacecrafts on round Jupiter to slingshot them out into the outer solar system and then it's going to fly back off away we're never going to see it again well what happened to it huh well it'll it'll it'll experience some very exciting and fun things around the Sun it may or may not make it round the Sun as we can talk about in a minute and then it'll just it'll just head back out become cooler become if it if it survives it'll it'll just wander off back into the outer solar system so a generic name for a comet is known as a dirty snowball which kind of reflects its composition it's rock it's ice it's some organic compounds and some gas all mixed up together when it's out in the cold reaches of the outer solar system it's just a lump it's not varying very much but as it plunges in towards the Sun it gets gradually heated and then interesting things start to happen material will vaporize off what you start off as a very solid ish lumpy nucleus that might be meters or kilometers across it will gain an atmosphere called the coma and that will be puffy and gaseous and and big and then what we think of with the comment where they get their name is from the tails that form and you can actually get two kinds of tails so if this is the coma this is the nucleus plus the outer atmosphere of our comet this comet is coming into the Sun and the material is now being heated and it's starting to stray you mount behind it and it's forming this beautiful tail that is probably largely made up of dust and that's what we tend to think of when we think about beautiful comments streaking across the sky and in fact the origin of the word comet refers to something with hair so these are hairy objects if you like and this comet this tail this is an important point it's not it's not following the direction of motion so it's not streaming out behind the comet in the sense that my hair might be blowing behind me if I'm running it's it's it can actually follow kind of a curved path as it gets left behind in this orbit so you can have kind of a curvy tail that's not the only kind of tail you have the second kind of tail is called an ion tail and this is the interaction of particles that are being pushed off the the comet's nucleus and they're interacting with charged particles from the solar wind and so if this is the Sun here the solar wind is pushing these this is this ion tail out in a straight line behind the comet and this is formed from interactions between material coming off the comet gas and the solar wind the stream of charged particles that is going out in all directions from the Sun and so this solar wind is going to push this ion tail back and it's going to be in a straight line the ion tail is always going to be pointing away from the Sun because of the solar wind the dust tail is can be slightly curved and is going to streak out behind the comet in in its orbit and an interesting thing about the dust tail is that that material can stay there in orbit around the Sun for a long time and our orbit on earth can intersect that remnant of dust and when that happens that's when we see these periodic meteor showers every year so the Perseids in August is a famous meteor shower that happens every year and that's because every year at that time the Earth's orbit sweeps through this leftover material from a comet and those tiny little particles burn up in the atmosphere and give us a great meteor show comet Ison was discovered in September 2012 and as its orbit was this is it was way out by the orbit of Jupiter's it was before it had any sort of spectacular tail or anything like that and as observations were taken and its orbit was plotted we started to realize that it was going to be one of these sungrazing comets and in fact it was going to come within about 1.8 million kilometers of the Sun at its perihelion its distance of closest approach that's three times the solar radius that's really really close at the time of filming I think nine different spacecraft have actually observed and will continue to observe comet Ison as it approaches the inner solar system so we're early November now 2013 we're a few weeks away from perihelion the big question is what's going to happen to Ison it may well be that it disintegrates before it even gets close to the Sun that's a possibility once it gets round the Sun it has to contend with temperatures of 5000 degrees it has to contend with the tidal gravitational field of the Sun which might may well tear it apart it's going to be traveling at 400 kilometres per second at that time to put that in perspective if we were to travel from the University of Nottingham campus here and not am to the University of Nottingham vez in Ningbo China if we did it that fast 400 kilometres per second it would only take us 23 seconds so it's going to whip around the Sun and if it makes it out the other side that's when we may well be in for a treat because then it will feel the full force of the solar wind of its orbital journey and that's when it may well brighten very very bright may be visible to the naked eye may if we're lucky have a beautiful long tail and we will be able to observe it very well it's not the most romantic of names Iceland stands for the international scientific optical network which was the coordinated survey of people using ground-based telescopes to look for comments

Channel: Sixty Symbols

Views: 141,871

Rating: 4.9603224 out of 5

Keywords: sixtysymbols, comet, astronomy, ison, tail, orbit, Solar System (Star System), Space

Id: DoypFpi5d4Y

Length: 9min 2sec (542 seconds)

Published: Mon Nov 18 2013