Assuming they’re made up of the same materials as Earth (metal and rock) and therefore have about the same density, you’d weigh 60 percent more on Kepler-62e, and 40 percent more on Kepler-62f. I’ll note that all things considered, neither would be paradise: Kepler-62e gets about 20 percent more sunlight than we do on Earth, and Kepler-62f gets about half; a bit hot and cold for my taste. But again, we don’t know the conditions on these planets. Give Kepler-62e a thin atmosphere, and Kepler-62f a thick one, and they might look a lot like Earth.

Lexicographic ordering is a pretty simple mathematical technique used to determine the best order a set of values should come in. It's most commonly used in libraries or dictionaries for arranging books and words, for instance, with the alphabet determining the order of the letters.

Murphy created two programs, LearnFun and PlayFun, and began recording himself playing the first level (world 1-1) of Super Mario Bros. The NES puts out 60 frames of 2048 bytes per second, and each of these was fed into LearnFun. Everything in the NES's memory—the buttons being pressed, the number of lives left, the score, the locations of enemies, Mario's position as coordinates, and so on—is taken in by the LearnFun algorithm.

Similar techniques have already been applied successfully in people with simpler tissue, such as windpipes. But the kidney is by far the most complex organ successfully recreated.

"If this technology can be scaled to human-size grafts, patients suffering from renal failure, who are currently waiting for donor kidneys, could theoretically receive an organ grown on demand," says Harald Ott, head of the team that developed the rat kidneys at the Massachusetts General Hospital in Boston.

The idea would be that traditional chemical rockets could deliver payloads to low Earth orbit and solar electric propulsion could then power a spacecraft to higher energy orbits, including Lagrange points or a potential assembly point in space between Earth and the moon. This approach could facilitate missions to near Earth asteroids and other destinations in deep space, NASA said.

Just as the volunteers started to fall asleep inside the scanners, they were woken up and asked to recount what they had seen.

Each image mentioned, from bronze statues to keys and ice picks, was noted, no matter how surreal.

This was repeated more than 200 times for each participant.

The researchers used the results to build a database, where they grouped together objects into similar visual categories. For example, hotel, house and building were grouped together as "structures".

The scientists then scanned the volunteers again, but this time, while they were awake and looking at images on a computer screen.

With this, they were able to see the specific patterns of brain activity that correlated with the visual imagery.

The researchers now want to look at deeper sleep, where the most vivid dreams are thought to occur, as well as see whether brain scans can help them to reveal the emotions, smells, colours and actions that people experience as they sleep.

Dr Mark Stokes, a cognitive neuroscientist from the University of Oxford, said it was an "exciting" piece of research that brought us closer to the concept of dream-reading machines.

"It's obviously a long way off, but there is no reason why not in principle. The difficult thing is to work out the systematic mapping between the brain activity and the phenomena," he explained.

The human volunteers wore electrode caps that monitored their brain activity using electroencephalography (EEG). Meanwhile, an anaesthetised rat was hooked up to a device that made the creature's neurons fire whenever it delivered an ultrasonic pulse to the rat's motor cortex.