On the horizon: news from the frontiers of science

Astronomers solve asteroid mystery, the origins of orchids, and why pigs should get credit for Europe's first farms.

Astronomers solve asteroid mystery

Imagine reconstructing an entire game of billiards from the last few shots.

That's akin to the "what dunnit" US and Czech astronomers assigned themselves. They were looking for the source of a surge in "impactor" collisions with Earth and the moon that peaked about 100 million years ago. The events include impactors that did in the dinosaurs some 65 million years ago and carved the crater Tycho on the moon.

Over the years, some researchers have argued that comets were the source; others said it was asteroids. The culprit, according to the new research: an asteroid the team has dubbed Baptistina, after a group of asteroids between Mars and Jupiter. The group is clustered around Baptistina 298, an asteroid discovered in 1890, and the group shares its chemical characteristics.

Combining observations of the asteroid group's current behavior with computer simulations to, in effect, run the picture in reverse, the team came up with this scenario: Some 160 million years ago, the 105-mile-wide parent asteroid was whiling away the eons near the inner edge of the asteroid belt when it was smacked by another asteroid about one-third its size. Roughly 20 percent of the largest shards, ranging in size from about a half mile wide to six miles across, were drawn into orbits that cross Earth's path around the sun.

The good news: "We are in the tail end of this shower," says William Bottke, a scientist at the Southwest Research Institute in Boulder, Colo., and a member of the team reporting its results in Thursday's issue of the journal Nature.

Ancient orchid discovery

A bee cloaked in orchid pollen and encased in fossilized tree sap has become Exhibit A in the case for an ancient lineage for the showy plants.

Orchids' evolutionary history has long been contentious. Some scientists have argued for a relatively recent rise some 26 million years ago, based in large part on a dearth of fossil evidence. Others argue for an older, 112-million-year-old lineage based on orchids' enormous diversity and their apparent relationship to asparagus, an ancient line in itself.

Enter the 15 million- to 20 million-year-old amber specimen, which came from a private collector. Scientists from the US, the Netherlands, and the Dominican Republic analyzed the pollen specimens. Comparing the physical characteristics of the pollen with those of other ancient plants, the team estimates that orchids arose between 84 million and 76 million years ago. They began to thrive after the mass extinction that ended the reign of dinosaurs 65 million years ago. The results appear in a recent issue of the journal Nature.

Pigs get credit for Europe's farms

The shift from hunting and gathering to farming as the main source of food began some 11,000 years ago in the Near East. One of the enduring puzzles for archaeologists has been the origins of farming in Europe.

To find out, says a global team of scientists, you must follow the pigs. Using DNA evidence from museum samples, they found that domesticated pigs from the Near East spread into Europe via two routes at least as early as 5500 BC and reached the region around what is now Paris around 4000 BC.

The team suggests that when early Europeans first encountered the domesticated pigs, they had a "Why didn't we think of that?" moment. Soon, they started to domesticate European wild boars. Once the European varieties emerged, genetic evidence for the imports all but vanishes. At the least, the team says, pig DNA tells a tale of complex interactions between newcomers and locals as farming moved onto the continent from the Near East. The results appear in the current issue of the Proceedings of the National Academy of Sciences.