On the horizon

This asteroid is all rubble

Images transmitted from Japan's plucky Hayabusa spacecraft have revealed new information about near-Earth asteroids.

That's the verdict several scientists have handed down to Japan's asteroid sample-return mission, which visited the asteroid Itokawa last fall. Writing in the current issue of the journal Science, researchers reported that the "otter-shaped" asteroid is not a single solid object, as they thought, but a collection of rubble roughly 0.2 miles across. That's a surprise, because scientists didn't think anything that small would have enough gravity to hold rubble together. Made of particles ranging in size from sand grains to boulders more than 50 yards across, the asteroid's overall density leaves it more porous than a pile of beach sand.

It's a weird place where sunlight levitates dust off the surface and solar wind "winnows" it, notes Erik Asphaug, at the University of California in Santa Cruz whose commentary accompanies the research results. "It is not clear why Itokawa is there at all.... But Itokawa hangs onto its pieces."

It's still unclear if the craft successfully scooped up samples from Itokawa. If the Hayabusa manages to stumble home after its ordeal, Japanese researchers expect it to arrive in 2010. Only then will they discover if their attempt at grab-and-go succeeded.

Biologists working in California have "rediscovered" what may be the bug world's equivalent of the Ivory-billed woodpecker: a type of millipede that comes the closest to sporting the insect's fabled 1,000 legs.

Until now, the first - and only - sighting of Illacme plenipes (with 750 legs) came in 1926. The Illacme scuttles again, according to two biologists from East Carolina University in Greenville, N.C. They captured 12 specimens - a mix of males, females, and juveniles - within a 200-acre patch of land in California's San Benito County, east of Monterey. Among the adults, the thread-thick creatures sported from 318 to 666 legs, depending on gender. And they display remarkable physical traits when viewed under a scanning electron microscope. Their results appear in Thursday's issue of the journal Nature.

The duo, biologists Paul Marek and Jason Bond, note that equally rare relatives have been found in biodiversity hot spots in Southeast Asia. They note that because the millipede is rare and occupies a tiny patch of the planet (within another biodiversity hot spot), "its fragile habitat must be protected at all costs."

Some 250 million years ago, the largest mass extinction in the planet's history occurred - paving the way for the age of the dinosaurs. Scientists from the US, South Korea, and Russia say the trigger may have been a 30-mile-wide meteor that punched a 300-mile-wide crater in Antarctica's crust.

The team cautions that the evidence is preliminary. Their discovery lies under a mile or more of ice. And it shows up only in remote-sensing images; no one has grabbed rock samples.

But, they add, the data come from different techniques than those used to spot features in Earth's crust and its underlying mantle. NASA's GRACE satellite measures subtle changes in Earth's gravity as it passes over features of varying density. GRACE picked up a 200-mile-wide concentration of mass in the mantle beneath eastern Antarctica's Wilkes Land area. To Ohio State University geophysicist Ralph von Frese, who led the team, this "mascon" looked similar to those underlying large craters on the moon. When the team looked at aircraft-based radar images of the land beneath the ice, they found a craterlike structure sitting atop the mascon.

The team acknowledges that more work needs to be done to confirm the find. They speculate that if their reading of the data is correct, the meteor could have created a rift in the crust that, 150 million years later, would widen, splitting present-day Australia from Antarctica. They reported their results during the recent meeting of the American Geophysical Union in Baltimore.