On the horizon

Diamond-studded planets?

Some planets in our galaxy could harbor an unexpected treasure: a thick layer of diamonds hiding under the surface, astronomers reported.

No diamond planet exists in our solar system, but some planets orbiting other stars in the Milky Way might have enough carbon to produce a diamond layer, Princeton University astronomer Marc Kuchner said at a conference Monday on extrasolar planets.

That kind of planet would have to develop differently from Earth, which is made up mostly of silicon-oxygen compounds and believed to have formed from a disk of gas orbiting the sun.

In gas with extra carbon or too little oxygen, carbon compounds like carbides and graphite could form instead of silicates, Dr. Kuchner said. Any condensed graphite would change into diamond under the high pressures inside carbon planets, potentially forming diamond layers many miles thick inside the planets.

The galaxy as a whole is becoming richer in carbon as it gets older, raising the possibility all planets in the future may be carbon planets, Kuchner said.

An engraving thought to be 10,000 years old has been uncovered in a cave, British researchers said.

The series of inscribed crosses - found on the wall of Aveline's Hole in Somerset, southwest England - are believed to date from the early Mesolithic Period just after the Ice Age.

"The few lines that form this panel are a signature from the period right at the end of the last Ice Age when the present period of warm climate was beginning," said Jill Cook from the British Museum's Department of Prehistory and Europe. "The pattern is comparable with others known from northern France, Germany, and Denmark, giving a wider context for the finds of this time and a rare glimpse of what may have been a rather special means of communication."

The discovery of the engraved crosses - at the site of the earliest known cemetery in the British Isles - follows the discovery of 12,000-year-old Ice Age engravings at Creswell Caves in Nottinghamshire, central England, two years ago.