On the horizon

Catacomb pioneers

Early Christians in ancient Rome have long been seen as the first to use the city's catacombs - an extensive network of underground burial chambers. Now researchers say they have uncovered evidence pointing to Rome's Jewish inhabitants as the catacomb pioneers.

Both communities shared the burial practice from roughly early in the 3rd century AD to the mid 5th century, they note. But pinning an origin down more precisely than that has been difficult. So a research team from the University of Utrecht in the Netherlands took wood samples from 10 catacomb construction sites, including the Jewish Villa Torlonia catacomb. After dating the samples, the team found that the Villa Torlonia site was used a full century before the earliest Christian catacomb.

Given the interaction between the Jewish and Christian communities in Rome over the centuries, and Christianity's theological roots in Judaism, it's likely that Christian funeral practices drew on those of the Jewish community, the team says. Indeed, they point out that the deacon in charge of building the Christian catacombs came from the Jewish quarter. The results appear in Thursday's issue of the journal Nature.

Researchers keep looking for tools for herding tiny cells and microscopic particles to separate the good, the bad, and the ugly. At these sizes, tweezers are definitely out of the picture.

Scientists have used lasers as tweezers. But such techniques can destroy some of the samples being moved, and they can manipulate only a limited number of cells. Now, a team of engineers has developed a new way to use light to push small particles around.

The team from University of California at Berkeley used the light from a far weaker laser to generate electrical fields in a piece of photosensitive silicon in what they call optoelectric tweezers. The team suspended the particles it wanted to herd in a liquid, then sandwiched the liquid between a piece of glass and the light-sensitive silicon. When the laser shone through the glass and onto the silicon, the particles either gathered at the spot or skittered away from it, based on their electrical properties.

The approach allows researchers to shuffle from 1 to 10,000 cells at a time. Combined with pattern-matching software, the technique could be a boon to biologists, they say. Their results are in Thursday's issue of Nature.

Astronomers traditionally have counted craters on an asteroid to determine the object's age. Now, a team of astronomers is casting doubt on this technique. But understanding how craters form may open an important window on how an asteroid is put together. Such knowledge is important if humans need to divert or demolish an asteroid that has Earth in its cross hairs.

In this case, the asteroid is 433 Eros. The team of Northwestern and Cornell researchers used images from the NEAR-Shoemaker spacecraft, which orbited Eros for nearly a year before landing on it in 2001. The team found that a large object erased smaller craters as it punched its own ding into the asteroid. But instead of covering other craters with ejected material from its own strike, the object sent seismic waves through the asteroid. The smaller craters filled in as loose material on the surface rearranged itself - much as shaking a sugar bowl smooths the top layer of sugar. The team concludes that crater counting is therefore a misleading way to date an asteroid.

But the approach also suggests that Eros is covered with a loose, gritty layer of material to depths of 10s of meters, with an interior solid enough to transmit collision shock waves throughout the object. The team reports its findings in Thursday's issue of Nature.

American astronomers are hoping to dodge yet another of nature's bullets. For the second time in a year, a wildfire is threatening a major mountaintop observatory. The $100 million Fred Lawrence Whipple Observatory, run by the Harvard-Smithsonian Center for Astrophysics, was evacuated last week as a fire advanced on its home on Mt. Hopkins, south of Tucson, Ariz. The observatory hosts a 6.5-meter telescope and several smaller telescopes.

In July 2004, Arizona's Mt. Graham International Observatory was evacuated as a wildfire rushed up its slopes. Lightning triggered this month's blaze, called the Florida Fire. So far, the fire has torched more than 22,500 acres, according to the National Interagency Fire Center in Boise, Idaho. Crews have been clearing the area around the observatory of brush and encircling it with a ring of fire-retardant chemicals.