A new type of jet engine could revive supersonic air travel - The Economist | How scientists went to an asteroid to sample the Sun - The Economist | Why chinstrap penguins sleep thousands of times a day - The Economist | Do rising methane levels herald a climate feedback loop?

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A new type of jet engine could revive supersonic air travel - The Economist

Since the 1960s engineers around the world have been fiddling with a novel type of jet called a rotating detonation engine (RDE), but it has never got beyond the experimental stage. That could be about to change. GE Aerospace, one of the world’s biggest producers of jet engines, recently announced it was developing a working version. Earlier this year America’s Defence Advanced Research Projects Agency awarded a $29m contract to Raytheon, part of RTX, another big aerospace group, to develop an RDE called Gambit.

Both engines would be used to propel missiles, overcoming the range and speed limitations of current propulsion systems, including rockets and existing types of jet engines. However, if the companies are successful in getting them to work, RDEs might have a much broader role in aviation—including the possibility of helping revive supersonic air travel.

In a nutshell, an RDE “replaces fire with a controlled explosion”, explains Kareem Ahmed, an expert in advanced aerospace engines at the University of Central Florida. In technical terms, this is because a jet engine relies on the combustion of oxygen and fuel, which is a subsonic reaction that scientists call deflagration. Detonation, by comparison, is a high-energy explosion that takes place at supersonic speeds. As a result it is a more powerful and potentially a more efficient way of producing thrust, the force that drives an aircraft forward.

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How scientists went to an asteroid to sample the Sun - The Economist

It was, Dante Lauretta told his audience at an American Geophysical Union meeting in San Francisco, like seeing an old friend after “seven years [and] a journey of 3bn miles”. Sitting in front of him in the Utah desert on the morning of September 24th, “a little charred and worse for wear”, was a capsule about the size of a washing-machine drum. The last time he and his colleagues had seen it had been when they had packed it up ready to be launched into space from Cape Canaveral in the summer of 2016.

In the intervening years the capsule had travelled to Bennu, a small asteroid in an orbit which crosses that of the Earth, as part of a mission called OSIRIS REx. In 2020 the mission’s main spacecraft briefly descended to Bennu’s surface and loaded the capsule with perhaps 140g of material. It then returned to the vicinity of the Earth, cast off the capsule and flew off to study another asteroid named Apophis. The capsule plunged into the atmosphere like an incoming meteorite; it failed to deploy its parachute in the way that had been planned (thus giving Dr Lauretta conniptions) but ended up safe and sound on the surface.

On December 11th Dr Lauretta provided the gathering with some preliminary results from his team’s analysis of its contents. Perhaps the most important was a negative one. The sample was pristine. Though bits of asteroids fall to the Earth every day as meteorites, they are not protected from the heat of re-entry or later contamination at the surface. The Bennu sample was.

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Why chinstrap penguins sleep thousands of times a day - The Economist

Sleep is a bit of an evolutionary mystery. A sleeping animal cannot look for food, defend its territory, flee from danger or find a mate. The fact that sleep is nonetheless ubiquitous among animals suggests its restorative powers are essential. So does the fact that, if laboratory animals are deprived of it for long enough, they die.

Some animals, though, try to have their cake and eat it. Dolphins and ducks can sleep with only half their brains at a time, leaving the other half alert. Now a paper in Science by Paul-Antoine Libourel from the Lyon Centre for Research in Neurosciences, and Won Young Lee from the Korea Polar Research Institute, reports another ingenious dodge. Chinstrap penguins, it seems, take their sleep in the form of thousands of tiny micro-naps—or at least, they do when they are nesting.

Dr Lee and Dr Libourel were examining penguins on King George Island, just off the coast of Antarctica. Keen to conduct sleep research in the wild, rather than in the confines of a laboratory, the researchers captured 14 penguins. They fitted them with electrodes to record their brainwaves, and fixed movement sensors and GPS trackers to their bodies. Thus equipped, the penguins were released, and their brain activity was tracked remotely for ten days. In addition, some were monitored at their nests by video cameras.

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Do rising methane levels herald a climate feedback loop? - The Economist

The end of an ice age is a fearsome and complex thing. Ice sheets collapse; ocean currents shift; weather patterns are thrown awry; low-lying land is inundated. Each change triggers more change, mostly in a way that makes the world warmer still.

Such “terminations” are visible in the geological record. When ice ages end, says Euan Nisbet of Royal Holloway, University of London, a sudden rise in airborne methane levels “is the bellwether, right at the beginning of [the] changes. The melting of the ice takes thousands of years. But the atmospheric change can be…a matter of decades.” And when Dr Nisbet looks at today’s atmospheric data, he sees something that looks worryingly termination-like.

At the end of an ice age, as the world begins to warm, its tropical wetlands spread. The microbes that live in those wetlands produce methane as a waste product, so more wetlands means more methane in the air. And because methane is itself a powerful greenhouse gas, that drives further warming in turn. Even as delegates to the COP28 climate conference consider ways to cut human methane emissions, Dr Nisbet worries that the Earth’s natural systems may be churning out more and more of the gas.

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