Composition and Structure
In 1986, the last time Halley's flew past Earth was the year that we first saw the heart of a comet. The core of Halley was pictured by both European and Russian efforts to learn more about this mass that visits us every 75 years. The core of a comet had not been seen previously as the comet is engulfed in a 'mini-atmosphere' otherwise known as a coma. The coma of Halley's can reach up to 100,000 km across, and is made up of vaporised ice and dust particles that have been ejected from the core, this occurs due to sunlight hitting the comet itself. The European spacecraft, named Giotto, and the Russian effort called VEGA, were able to fly through the tail of the comet and photograph the core itself which allowed scientist on both projects to see the shape and size of the comet. The size of the comet was at the time 16 x 8 x 8 kilometres (or 10 x 5 x 5 miles), and is shaped like a peanut. If Halley's Comet, however unlikely hit Earth, due the velocity and sheer size, the impact would cause a global cataclysm.[2]
The pictures taken by the two spacecraft, Giotto and VEGA, revealed that of the light that it receives the comet nucleus only reflects about 4% and absorbed the rest, typically less than coal, thus inferring that the comet is darker than coal, it is also less light than black velvet reflects. The nucleus is extremely black, and the comet only shines brightly when we see it because as it gets closer to the sun dust and vapour gets emitted and burnt off, this causes the bright coma that is visible whenever it appears in our skies. As hypothesized, Halley's Comet has supposedly shrunk by up to 90%, which means that only a small fraction of what was originally there is left to orbit the sun. It has also been suggested that the dark material that is left is actually dust and very complex molecules which have remained in the 1024 cubic kilometre mass. Supposedly, during previous close encounters with the sun, more volatile ices and compounds have been ejected from the comet. [2] [3]
The pictures taken by the two spacecraft, Giotto and VEGA, revealed that of the light that it receives the comet nucleus only reflects about 4% and absorbed the rest, typically less than coal, thus inferring that the comet is darker than coal, it is also less light than black velvet reflects. The nucleus is extremely black, and the comet only shines brightly when we see it because as it gets closer to the sun dust and vapour gets emitted and burnt off, this causes the bright coma that is visible whenever it appears in our skies. As hypothesized, Halley's Comet has supposedly shrunk by up to 90%, which means that only a small fraction of what was originally there is left to orbit the sun. It has also been suggested that the dark material that is left is actually dust and very complex molecules which have remained in the 1024 cubic kilometre mass. Supposedly, during previous close encounters with the sun, more volatile ices and compounds have been ejected from the comet. [2] [3]
Due to the dark nature of the nucleus of the comet itself, the programming of the Giotto spacecraft and on-board cameras, and the delay between commands from the controllers on Earth to the spacecraft, there was a chance that Giotto could have flown right past the comet core. This is because the cameras were programmed to picture the brightest object that was analysed from the core of the comet, as astronomers thought that the comet would be highly reflective because of the prediction that the comet would be made of highly reflective ice. This meant that the on-board computers and cameras should have flown right past the comet with no visual information relayed back to Earth, however, the comet had jets of escaping material, probably vapour and dust, ejecting from a geyser like point, which was in fact a source of extremely bright light, on which the cameras centred themselves on. This meant that although most of the pictures did not centre on the nucleus itself, but the vents, however, for the most part, the core is visible on the pictures taken and seen to the side of each photograph.
Photographs from Giotto showed that the geysers were only active when in in sunlight, as became dormant when in darkness, they shut down very quickly when the light was no longer targeted at the vents. The pictures also showed that the comet was littered with craters, and that the vents make up around 10% of the surface of the comet core.[2]
Photographs from Giotto showed that the geysers were only active when in in sunlight, as became dormant when in darkness, they shut down very quickly when the light was no longer targeted at the vents. The pictures also showed that the comet was littered with craters, and that the vents make up around 10% of the surface of the comet core.[2]