Recipe for moon’s magnetic field: Stir it!

When astronauts from the 1969 Apollo 11 mission returned to earth with about 50 pounds of lunar rocks and soil, scientists were surprised to find that some of the samples were magnetised.

The moon has no magnetic field, so it must have had an unknown magnetic past. Some scientists thought that past was limited to daylong surges of magnetism created by asteroid impacts, but in 2009, an analysis revealed lunar rock so weakly magnetised that it could have formed only by cooling slowly under the influence of a steady magnetic force.

At some time the moon must have had an earth-like magnetic field. But how? “If the earth were moon-size,” said Christina Dwyer, a planetary scientist at University of California, Santa Cruz, “it wouldn’t have a magnetic field.” Internal temperature differences would not have been great enough to roil its liquid outer core and drive the magnetic dynamo.

Two new studies, both published in Nature, suggest what may have happened: If the moon’s mantle rotated against its outer core (which was and may still be molten), it would churn the outer core like a coffee stirrer when it switches abruptly from clockwise to counterclockwise.

One theory of what caused the opposing rotations, posited by Dwyer’s team, is that the earth’s strong tidal pull on the closer, infant moon torqued its mantle against the core. The other theory, suggested by Michael Le Bars of the Research Institute for Out-of-Equilibrium Phenomena in Marseille, France, and others, is that intermittent asteroid collisions may have spun the mantle around like a basketball for 10,000 years at a time.

Pacific sealife faces camouflage dilemma
About half a mile below the surface of the Pacific Ocean, small squid and octopuses face a camouflage conundrum. Some of their predators like hatchet fish, hunt by diving deeper and looking upward for silhouettes of potential food. To sneak past them, it helps to be transparent and avoid casting a shadow. But other predators, like deep-sea dragonfish, patrol using biological searchlights that reflect off clear flesh.

In the presence of these luminescent foes, it’s much safer to be as dark as the surrounding water. New research shows that at least two species of cephalopod, a Japetella octopus and an Onychoteuthis squid, have avoided this dilemma by evolving the ability to switch rapidly between the two disguises.

“In less than a second, it’s on and off,” said Sarah Zylinski, an ecologist at Duke University and an author of the study, which appeared in Current Biology. o alternate camouflage, the two cephalopods rely on distributed sacs of black pigment, which they can twitch like muscles. When it’s dark and the cephalopods want to be transparent, the sacs form compact spheres, allowing the animals’ glassy flesh to show. But when a light appears, the sacs flatten and stretch toward one another, shrouding the creatures in pigment.

Egalitarian society of muriqui monkeys
The muriqui monkeys of the Atlantic Forest in Brazil, a highly endangered species numbering only about 1,000, live in an egalitarian society. Females are as muscular as males. Males do not compete to be alpha monkeys. Even when it comes to mating, males tend to simply wait for their turn instead of fighting.

Karen Strier, an anthropologist at the University of Wisconsin who has been observing them for 29 years, and her team recently used DNA analysis to determine who fathered each of 22 muriqui babies. Their research, which appeared in Proceedings of the National Academy of Sciences, shows that while there were no superdads, some males did have a slight edge.