On the Horizon: News from the Frontiers of Science

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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. …