14 | NewScientist | 30 April 2011

A SQUIRT of bubbles can act like a liquid or a solid depending on its density – a feat thought unique to grainy materials such as sand.

Pour sand, seeds or powder down a chute and they can flow like a liquid. But if the grains are packed so that they fill 64 per cent or more of the chute, they jam up and behave like a solid. The grains are thought to start moving with their neighbours, forming

temporary “necklaces” that resist flow, although it is unclear why the transition occurs at this point.

To investigate whether bubbles behave in a similar way, Rémi Lespiat and his colleagues at the University of Paris-East in France squirted nitrogen gas into a chamber of water and monitored the resulting bubbles’ passage through a tube.

At low densities, the bubbles

Geyser moon puts its mark on Saturn

AN ELECTRICAL current is flowing from Saturn’s moon Enceladus to the ringed planet, creating a glowing patch in the planet’s atmosphere.

Ultraviolet images taken by the Cassini spacecraft revealed the patch, which is distinct from the planet’s auroras. It lies near Saturn’s north pole – exactly where electrons emitted by Enceladus would hit after being chanelled along the planet’s magnetic field lines, report Wayne Pryor of Central Arizona College in Coolidge and colleagues (Nature, DOI: 10.1038/nature09928).

Where do the electrons come from? The team believes that sunlight knocks them off water molecules spewed by geysers at Enceladus’s south pole.

The brightness of the patch varies, which could be due to variations in the amount of water vapour released by Enceladus, says the team.

Chimeric clue to origin of colonial animals

WIDESPREAD chimerism has been found for the first time in a single, free-living animal: the dahlia anemone.

Chimeras carry the genetic material from two or more embryos that fused during development. They are common among corals and other colonial animals but were thought rare in species of solitary animals.

Annie Mercier of Memorial University in Saint John’s, Newfoundland, Canada, and colleagues suggest otherwise. Watching a group of female dahlia anemones (Urticina felina) release their larvae, they were surprised to see that some larvae had fused together.

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Bubbles jam just like grains of sand flowed. But when they filled 64 per cent of the tube, they jammed just like the grains (Physical Review Letters, DOI: 10.1103/PhysRevLett.106.148302). The result suggests there may be a universal rule that kicks in when objects fill 64 per cent of a space.

“It’s surprising that they get the same figure,” says Randall Kamien at the University of Pennsylvania in Philadelphia. He suggests using the insight to evenly mix bubbles of gases for medical applications.

“We thought, this is really strange,” Mercier says. Further study showed that around 3 per cent of

young were visibly chimeric, and some developed into two-headed adults. If one of these partners was prodded gently, both retracted their tentacles and closed up – indicating they shared a nervous system (Proceedings of the Royal Society B, DOI: 10.1098/rspb.2011.0605).

Mercier thinks chimeras are probably even more common than that: she found that many chimeric larvae became almost indistinguishable from normal animals as they developed. They were, however, larger than normal as juveniles. If that gives the chimeras a competitive advantage over their non-chimeric relatives, the new finding could reveal how and why animals like corals became colonial, says Mercier.

DOING nothing to stop a crime can be seen by others to be as bad as committing the crime directly.

So says Peter DeScioli at Brandeis University in Waltham, Massachusetts, who presented students with a number of scenarios that led to a fatality. An actor whose hesitancy to act led to the death was seen as less immoral than an actor whose direct actions led to the death. But the students judged deliberate inaction that led to the fatality as equally immoral as direct action that caused the death (Evolution and Human Behavior, DOI: 10.1016/ j.evolhumbehav.2011.01.003).

DeScioli thinks the results show we see inaction as less immoral only because we typically lack proof that it was deliberate.

The immorality of deliberate inaction