11 October 2026 (Sun)

Coming home from the space station is a more delicate business than going up. A capsule circling at eight kilometres a second has to lose that speed against the air, and its underside glows at thousands of degrees while it does. Parachutes open, it settles on the sea, and a ship comes alongside to lift it out.

The four who went up in February circled the Earth more than 3,792 times in 237 days — over 160 million kilometres. Among the things they did were growing stem cells in orbit and testing a device that makes intravenous fluid where it is needed. Far from Earth you cannot have medicines shipped out, so the way to make them on the spot has to be learnt in advance. One of the crew made four spacewalks this time, bringing her career total to seven, and another became the first French woman to go outside the station.

The Navier–Stokes equations describe how water and air flow. Everything from an aeroplane wing to the weather is worked out with them. Yet for almost a century mathematicians have not known one thing: does a solution stay smooth for ever, or can a place appear where the speed shoots up to infinity? That question is one of the seven problems carrying a million-dollar prize.

OpenAI said it ran ten thousand AI agents on a model it has not released for eighty-eight hours and obtained a proof that, under certain conditions, such a place does appear. The proof was checked line by line by a program called Lean. But what Lean checks is that the written statements do not contradict each other. Whether those statements really say what the original problem says is for people to judge. Researchers working on the same question by other means raised objections about credit at around the same time, and how much has actually been settled is still unresolved.

Fusion means joining two atomic nuclei to release energy. To join, they must be hot and tightly packed. To reach the state where the fire feeds itself — ignition — temperature, density and confinement time all have to be pushed past a certain line.

Researchers at the Princeton Plasma Physics Laboratory worked through the route to that line again. Usually the density is raised first and the heat added after. By their calculation, swapping the order — heat first, density second — lets you slip past the hardest stretch, going round the mountainside rather than over the peak. They worked out something else along the way: tungsten, the metal meant for the reactor walls, nearly doubles the pressure needed for ignition if as little as one part in ten thousand gets into the plasma.

A body too light to light its own fusion fire is called a brown dwarf. In a pair some 300 light-years away, a small star of about eighty-five Jupiter masses and a brown dwarf of about twenty-five circle each other very closely indeed: one lap every 87 minutes, the whole orbit small enough to fit inside the Sun.

That close, the outer gas of the lighter body is pulled towards the heavier one. Where the gas strikes the star a bright spot forms, and as that spot swings in and out of view the brightness traces a regular, triangular pattern. From the pattern alone the system looked at first like a neutron star stripping a companion — but the measured wobble was far too small for anything that heavy. The star is taking about one hundred-thousandth of an Earth mass a year, so the meal could last anywhere from hundreds of thousands to billions of years.