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Advanced search. Skip to main content Thank you for visiting nature. Abstract ALTHOUGH comets have been studied throughout most of recorded history, a detailed understanding of their internal properties is still lacking. Access through your institution. Buy or subscribe. Rent or Buy article Get time limited or full article access on ReadCube.
References 1 Shoemaker, C. Icarus submitted. Google Scholar 15 Chodas, P. Solem Authors Johndale C. Solem View author publications. Buy or subscribe. Rent or Buy article Get time limited or full article access on ReadCube. References 1 Sagdeev, R. Google Scholar 4 Keller, H. Google Scholar 6 Combes, M. Google Scholar 9 Whipple, F.
Google Scholar 14 Kiang, T. Google Scholar 17 Feldman, P. Google Scholar 18 Krasnopolsky, V. Google Scholar 19 Krankowsky, D. Google Scholar 23 McCoy, R. Google Scholar 24 Boyarchuk, A. Google Scholar 28 Greenberg, J. Google Scholar 29 Donn, B. Google Scholar 30 Weissman, P. Google Scholar Download references. Moroz Authors R. Sagdeev View author publications. View author publications. Rights and permissions Reprints and Permissions. About this article Cite this article Sagdeev, R.
Copy to clipboard. Groussin , N. Attree , Y. Brouet , V. Ciarletti , B. Davidsson , G. Filacchione , H. Fischer , B. Gundlach , M. Knapmeyer , J. Knollenberg , R. Kokotanekova , E. Leyrat , D. Marshall , I. Since comets are moving very quickly through the inner solar system, they only spend a few months in the part of the solar system where they are warm enough to sustain a substantial rate of mass losss.
Then, how much total mass does a comet like Halley lose with each passage through the inner solar system? A real comet might not lose mass at the same rate with every passage by the Sun; however, the general idea that a comet has a finite number of passages before it gets used up is clearly correct.
But a comet might "turn off" before being reduced to nothingness. With each passage, ices are preferentially lost and dust is preferentially left behind. Thus, a comet will develop a surface layer that becomes enriched in dust, i.
Eventually, such a comet may turn so black and develop such a good insulating surface that it will turn off, continuing in its orbit but no longer looking or behaving like a comet. Clearly, comets can't do this forever. And if we accept the Copernican Principle, that this time in the history of our solar system is not special, then new comets have been appearing and getting used up for the entire history of the solar system. Assuming the solar system is approximately as old or older than the oldest Earth rocks 3.
If there are billion 10 13 comets and each contains 10 14 kg of gas and dust, this is a total mass of. This is a fair amount of stuff!
Comets are sources of water. One could think of comets as possible future sources of water to bring to Earth or to a space station or to a planet like Mars. Alternatively, one could wonder whether the Earth's present abundance of water was deposited here by impacts with comets, early in Earth's history. The Earth's oceans contain kg of water. This is equivalent to 1 million Comet Halley impacts. Comets collide with planets.
This must not be a rare event the Copernican principle. What would be the significance of a comet hitting Earth?
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