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EVIDENCE of life on Mars may have already arrived on Earth, hidden inside white meteorites made of sedimentary rock. That’s the new hope, at least.

So far, all meteorites from Mars have been made of volcanic rock. But sedimentary rock, laid down in ancient Martian oceans, may be the best place to look for evidence of alien life, since water is a life-friendly environment.

To see if such sedimentary meteorites could even survive the trip to Earth, Frances Westall and colleagues at the European Space Agency’s STONE-6 project glued two sedimentary rocks containing fossils and other life signatures to the heat shield of an uncrewed Russian space capsule in orbit.

Over half of each 4-centimetre-wide rock melted during re-entry, but the traces of life were still detectable. Samples of living bacteria coated on each rock died, but their charred remains survived.

The quartz crust of each rock fused to a creamy white colour. So meteorite hunters, who usually search for dark rocks, should be looking for lighter shades, says Westall, who presented the results at the European Planetary Science Congress last week.

Best meteorites for Martian life

ADULT mouse cells have been “reprogrammed” back to an embryonic state without the introduction of cancer-causing genes. The feat raises hopes that induced pluripotent stem cells, which can potentially be turned into almost any cell type, will one day be transplantable in people.

Previously, iPS cells have been made using retroviruses carrying four genes that erase the developmental history of an adult cell . However, the method is not safe because retroviruses also add extra copies of potentially cancer-

causing genes to the chromosomes of the cells they infect. So a team led by Konrad Hochedlinger of the Massachusetts General Hospital in Boston used adenoviruses – which do not tend to integrate into a cell’s chromosome – to deliver the same four genes to mouse liver cells.

The cells reverted to an embyronic state and seemed safe. When iPS cells made using retroviruses are injected into mouse embryos, the resulting “chimeric” mice are prone to cancer, sometimes as early as

four weeks after birth. The chimeras made by Hochedlinger‘s team had not developed tumours even after 13 weeks (Science, DOI: 10.1126/science.1162494 ).

A difficulty of using adenoviruses is their inefficiency: with retroviruses, up to 10,000 adult cells are required to produce one colony of iPS cells, and this is 100 times as efficient as Hochedlinger’s procedure. However, George Daley , a stem cell biologist at the Children’s Hospital Boston, says the results are a key proof of principle.

Regenerative mouse cells take a step towards safety

WHEN honeybees dance to point their hivemates towards nectar-rich flowers, they waggle in a slightly different direction each time. It is sometimes claimed that this variability benefits the hive by helping bees locate new resources, but an experiment by David Tanner and Kirk Visscher from the University of California, Riverside, seems to have overturned this theory.

By observing bees trained to visit artificial sugar-traps, Tanner and Visscher discovered that rather than picking a flight path based on the angle of any one waggle, the bees flew off in a direction that more closely matched the mean angle of several waggles (Behavioral Ecology and Sociobiology, DOI: 10.1007/s00265-008-0619-z). “Bees apparently keep a mental log of the directions indicated in the dance,” says Tanner. “I find it remarkable that, with a relatively simple brain, they can do something so mathematically complex.”

Tom Seeley at Cornell University in Ithaca, New York, who has studied several aspects of honeybee societies, says he finds the study convincing. He adds, however, that the bees may not have been relying solely on the waggle dance when deciding which direction to fly off in. They could also have taken their cue from bees returning to the hive, he says, “for example by orienting to the flights of these bees as they flew to or from the feeder”.

How to make a beeline for food

SATELLITE galaxies have a hard time of it, as their bigger neighbours brutally rip away their ability to make stars. However, it seems the process is not quite as violent as was thought, which would explain the puzzlingly long time over which some satellite galaxies continue to form stars.

In theory, a satellite galaxy orbiting a massive cluster of galaxies at high speed should gradually lose its gaseous halo, depleting all its star-forming material by the time it is pulled into the cluster . Yet recent observations by the Sloan Digital Sky Survey have shown blue, star-rich

satellite galaxies mixed up with larger, red, star-poor clusters, suggesting that the satellites cling onto some star-forming ability even after entering the cluster .

To find out why, Andreea Font of the University of Durham, UK, and colleagues used a supercomputer called the Cosmology Machine to simulate the mechanics of the halo-stripping process. This indicated that around 20 per cent of the halo remains when the satellite reaches the cluster, sustaining their blue colour for longer (www.arxiv.org/abs/0807.0001).

The study could be an important step forward in our understanding of galactic evolution, says Alan Heavens at the University of Edinburgh, UK.

Outsider galaxies keep their haloes

www.newscientist.com 4 October 2008 | NewScientist | 17