Jupiter's largest moons don't go completely dark when the giant planet blocks their sunlight, astronomers have found.

The discovery could reveal more about Jupiter's mysterious upper atmosphere, which the researchers suspect is responsible for keeping the moons lit when they are not directly illuminated by the sun. This research could also help scientists better understand the atmospheres of alien planets, study team members said.

In 2005, Stanford scientist Karl Deisseroth discovered how to switch individual brain cells on and off by using light in a technique he dubbed 'optogenetics'.

Research teams around the world have since used this technique to study brain cells, heart cells, stem cells and others regulated by electrical signals.

However, light-sensitive proteins were efficient at switching cells on but proved less effective at turning them off.

Now, after almost a decade of research, scientists have been able to shut down the neurons as well as activate them.

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