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A snowy dustball


A dusty comet. So it appears the comet 67P to initial investigations conducted by JADE instrument on the spacecraft of the European Space. Alessandra Rotundi (INAF-IAPS and Parthenope University of Naples), Principal Investigator of JADE: “The birth and the evolution of the coma of 67P is a history of which just the beginning was turned out, and it is already exciting. We will wait a year, and perhaps more, to measure and to really know the whole.
More than a “dirty snowball” (“dirty snowball”), namely, in which predominates the volatile component (the ice), it is a “snowy dustball” (“ball of snowy dust “). So it appears as the comet 67 / P Churyumov-Gerasimenko researchers JADE tool dedicated to the analysis of cometary dust. The results were published in the journal Science some weeks ago under the special volume dedicated to the ESA Rosetta mission.

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Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

“This result – explains Alessandra Rotundi INAF-IAPS and Parthenope University of Naples, first signatory of the article and responsible (Principal Investigator – PI) instrument JADE – suggests that the 67P / CG is a very “dusty” comet, and those who work on the tools dedicated to the dust cannot be happy about that. ”
Within the study of comets it is important, in fact, to have information that will help us understand how comets are formed and how they evolve, what is the structure of the comet’s nucleus and, more particularly, to define the abundance of non-volatile component (refractory) than that volatile (ice), defined in the summary of the ratio in mass between dust and ice (“dust to gas ratio”) present at the surface of the core. It studies what are the core issues to be able to explore the interior.
“The information obtained from the instrument JADE – continues Alessandra Rotundi – together with that obtained from the images acquired from the OSIRIS room on dust grains that make up the hair of comet 67P / CG, allowed to go back to the mass of dust that 67P / CG issues . This amount, combined with the measures on the foliage of gas made by MIRO and ROSINA instruments (published on the same volume of Science ed.), allowed us to determine the ratio, dust to gas ratio, which was found to be 4 ± 2”.
“This number – adds the professor – deviates enough from those previously determined for other comets (e.g. 2 for the comet Halley). The value obtained for the comet 67P / CG suggests a minor percentage of the volatile component of other comets. But it is a result of the first period of cometary activity, and may change the approach of the comet to the sun. For the next perihelion (the point of minimum distance between the comet and the Sun) in August 2015 is expected a value of dust to gas ratio of three. ”
In the article in Science, the results show then another important issue regarding the orbiting grains. It is a family of grains which is distinguished from the grains emitted from the nucleus because coupled with the gas they are produced by the sublimation of the ice. The orbiting grains are characterized by large size (from centimeters to a few meters) and that they are issued by the sublimation of the ice only in periods of very intense cometary activity that is at perihelion. Then they were issued during the previous perihelion passage of the comet and, with decreasing intensity cometary, were “detained” in orbit from the comet nucleus.
“The birth and the evolution of the coma of 67P / CG – concludes the PI of JADE – is a history of which it turned out just the beginning, and is already exciting. We will wait a year, and perhaps more, to measure and to really know the whole. Certainly it is a promising start, as well as fascinating. “

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