22 February 2014 | NewScientist | 19

Sloshing sea may heat wonky moon

TRITON is really stirring things up. Neptune’s largest moon may

have a turbulent ocean under its icy crust, driving geologic activity. If so, the mix of liquid water and an ability to cycle nutrients within it hints that Triton has at least some of the ingredients needed to spark life.

Triton has an unusually smooth surface and shows signs of geysers and ice volcanoes, suggesting its icy crust is active. But it is too far away from the sun for our star to be providing enough heat for these features.

Triton is thought to be a former neighbour of Pluto, captured long ago by Neptune’s gravity. Getting snared would have put the moon under intense gravitational forces, says Francis Nimmo at the University of California, Santa Cruz, and the heat would have been more than enough to melt the ice.

If the moon kept some internal heat, it may support a liquid ocean underneath its icy shell. Nimmo and John Spencer at the Southwest Research Institute in Boulder, Colorado, modelled what such an ocean might be like now (Icarus, doi.org/rgc). Triton is significantly tilted with respect to Neptune, so that the planet squeezes and stretches the moon as it orbits. That could be driving turbulence in the ocean, the pair says, producing enough heat to set the ice above it in motion.

Legacy of empire visible in our genes

WE CAN see the impact of major chapters in history, like the Mongol conquests, in our genes today.

Garrett Hellenthal of University College London and colleagues have found a way to tell if the ancestors of two populations have mixed, and when. They analysed DNA from 95 groups around the world to find sequences each had in common with the others. Groups with more shared DNA were closely related, while longer shared chunks indicated recent mixing (Science, doi.org/rgk).

The DNA shows Genghis Khan’s army had a genetic impact. Six groups

from across Asia gained Mongol DNA between 1250 and 1300, when the Mongol empire was at its height.

The results also suggest that northern Pakistan’s Kalash people mixed with Europeans around 200 BC. That gives a little credence to their belief that they descend from Alexander the Great’s army, “though there are of course other possibilities”, says Hellenthal.

“Never before has genetics yielded such a high-resolution picture of population migrations and mixing,” says Anna Di Rienzo of the University of Chicago.

A MONKEY controls the hand of its unconscious cage-mate using thought alone. That may sound like animal voodoo, but it’s a step towards returning movement to people with spinal cord injuries.

The hope is that one day people who are paralysed could have electrodes implanted in their brains that pick up their intended movements. These electrical signals could then be sent to their paralysed muscles. Ziv Williams at Harvard Medical School in Boston wanted to see if sending these signals to nerves in the spinal cord

would also work, as this might ultimately give a greater range of movement from each electrode.

His team placed electrodes in a monkey’s brain, connecting them via a computer to wires going into the spinal cord of an anaesthetised monkey. The paralysed monkey’s hand was strapped to a joystick, controlling a cursor that the other monkey could see on a screen.

Williams’s team recorded the conscious monkey’s brain activity and worked out which signals corresponded to the back and forth motion of the joystick.

Through trial and error, they deduced which nerves to stimulate in the spinal cord to produce those movements in the anaesthetised monkey’s hand. When both parts were fed to the computer, the conscious monkey was able to move the other’s hand to make the cursor hit a target (Nature Communications, DOI: 10.1038/ncomms4237).

“It’s the first demonstration of brain-to-spinal-cord information transmission between two animals,” says Rajesh Rao at the University of Washington, Seattle.

Monkey voodoo holds key to movement in paralysed people

Drug helps blind mice see the light

IF IT’S beyond repair, replace it. This approach could soon be taken with rods and cones, the light-sensitive cells in eyes that can wither as we age, causing blindness. A drug has been found that coaxes neighbours of ailing cells to do the job for them.

In 2012, Richard Kramer at the University of California, Berkeley, discovered that injecting a certain chemical into the eyes of blind mice made normally light-insensitive ganglion cells respond to light. These cells ferry optical signals from the rods and cones to the brain, so the mice regained some ability to see light.

But it only worked with ultraviolet light. Now, Kramer’s team has found a different drug that does the same with visible light. Just 6 hours after they were injected, blind mice could learn to respond to light in the same way as sighted mice – although Kramer says he doesn’t know whether they regained vision or just light sensitivity (Neuron, DOI: 10.1016/j.neuron.2014.01.003).

Gene therapy and stem cells are also being explored as ways to restore sight, but a drug would be simpler and any side effects should be reversible, says Kramer.

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