Science Frontiers ONLINE No. 86: Mar-Apr 1993 | |
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The genesis of a cosmic "dust bunny". The nebulous meteor of July 29, 1970, as observed over Dover, England. |
(Kerr, Richard A.; "Magnetic Ripple Hints Gaspra Is Metallic," Science, 259: 176, 1993.)
At the low end of the density spectrum, we now find that Pluto's moon, Charon, and some of Saturn's moons have very low densities (1.2-1.4), meaning they are probably mostly water ice. Such density figures come from direct observation of these objects' volumes combined with mass estimates from their orbital dynamics.
(Crosswell, Ken; "Pluto's Moon Is a Giant Snowball," New Scientist, p. 16, November 21, 1992.)
Comment. How did this curious mix of ice and iron objects originate? Did some ancient collision demolish a planet with an iron core (like the earth"s) and an icy exterior?