The Week in Space and Physics: A Room Temperature Superconductor?
On LK-99, the demise of Aeolus, unexpected solar gamma rays and Voyager 2
The discovery of a room-temperature superconductor would change the world. Engineers have a long list of problems they could solve if only they had one, covering everything from super-efficient electrical grids to the memory circuits of quantum computers. No wonder scientists have spent decades searching for one.
Unfortunately the search has produced little in the way of solid results. The closest confirmed candidate so far is a substance known as lanthanum decahydride, which superconducts at -23°C (-10°F), but only when placed under millions of atmospheres of pressure.
That, then, explains why a recent pair of papers published on Arxiv have attracted so much attention. In them, a group of Korean researchers claim to have found an ideal superconductor; one that works at room temperature and under normal pressure. If they are correct it is an astounding breakthrough. For its discoverers it promises worldwide fame, for the rest of us it promises technological revolution.
Yet the papers have been met with broad skepticism by the scientific community. For one thing, room-temperature superconductivity is a hard problem. While superconductivity is well proven at low temperatures - those close to absolute zero - it has never been seen at anything like room temperature and pressure.
For another, the field has a history of big claims that end in disappointment. Earlier this year, for example, the physicist Ranga Dias claimed the discovery of a room temperature superconductor. Though that claim has not yet been disproven, an air of controversy lingers over Dias. Several papers by him, including another on superconductivity, have been retracted after evidence emerged that he had faked the results.
The Korean papers focus on a substance known as LK-99. This, a mixture of lead, copper, phosphorus and oxygen, appears to be fairly easy to make. In tests the researchers said the electrical resistance of LK-99 fell to zero at room temperature, a key sign of superconductivity. They also released a video of the substance levitating above a magnet, another common feature of superconductors.
Unfortunately, attempts to recreate the results in other labs have run into difficulties. Researchers in China and India created their own samples of LK-99 and repeated the experiments, but found no signs of superconductivity. The Condensed Matter Theory Center, part of the University of Maryland, said this week that they too do not believe LK-99 is a superconductor.
These are not good omens for LK-99. True, labs will take time to complete their investigations, and there is still a chance that someone credibly observes superconductivity in the material. But in all probability the dream of a room temperature superconductor is still far off.
Fortunately, it is also too early to write that dream off for good. No known theory of physics rules out the prospect of superconductivity at room temperatures and pressures. One day, hopefully, the claims will turn out to be true.
The Demise of Aeolus
For five years Europe’s Aeolus satellite mapped the Earth’s winds, tracking the ebb and flow of the atmosphere with a sophisticated ultraviolet laser. It was the first satellite to do this, and was, therefore, the first to give us a global view of the air flowing around our planet.
That proved useful for weather forecasters, who universally praised the data coming from Aeolus. But it also helped track events of global significance. In one case Aeolus monitored the plume from the vast Hunga Tonga volcanic eruption reaching far into the stratosphere. In another it helped fill the gap in weather data after Covid-19 grounded much of the world’s airliners.
In April, however, Aeolus’ scientific mission came to an end. Fuel was running low, operators said, and the satellite would not be able to maintain its orbit for much longer. At that point Aeolus was flying at a height of three hundred and twenty kilometers, which could have seen it naturally re-enter within months.
Instead ESA chose to steer the spacecraft into the atmosphere, aiming for re-entry over the southern Atlantic Ocean. Partly this was out of safety concerns. Had they left it to an uncontrolled re-entry, fragments of the satellite could have ended up smashing into a populated area.
Yet ESA also took it as an opportunity to show their commitment to ensuring space stays clear of debris. The number of satellites has boomed in recent years, and clouds of debris have grown more common. For satellite operators this represents a danger: the more stuff there is in space, the greater the chances of a collision.
ESA have thus stressed the importance of operators cleaning up after themselves. Under the agency’s “Zero Debris” strategy, all new satellites will soon have to be equipped with foolproof methods of disposal. Those in low orbits, like Aeolus, will need to find a way to deorbit. Those in higher orbits, from which re-entry can take centuries, will be put into special graveyard orbits.
But while the Zero Debris strategy sounds good, ESA will need the cooperation of other space agencies and companies to have a real impact. Most satellites, it is true, are not under ESA’s purview. Even when they are, disposal can happen long after the original owners of a satellite have vanished. The re-entry of Aeolus is a statement of intent, but ESA will need to do much more if they are serious about cleaning up space.
Gamma Rays and a Solar Mystery
Around a decade ago researchers spotted flashes of gamma rays coming from the Sun. These, they eventually concluded, were caused by energetic cosmic rays hitting the Sun.
Yet the results were somewhat puzzling. Theory said that the impact of cosmic rays on the Sun should be invisible to us, as any particles or energy released would fall back into the Sun. Only on rare occasions could that energy escape, appearing as a flash of gamma radiation. Observations, however, showed far more flashes than predicted.
This probably has something to do with the Sun’s magnetic fields, though exactly what is still unknown. It also seems linked to the eleven year cycle of activity that the Sun follows. In years of high activity the number of gamma rays falls away, in years of low activity it increases. This, researchers suggest, is because the solar wind increases in strength when the Sun is more active, pushing away cosmic rays.
In a recent paper, however, researchers reported spotting bursts of gamma rays far brighter than before. These are much more energetic that the cosmic ray theory should allow, suggesting that something else is happening in the Sun.
Despite the usual ideas that dark matter is somehow involved, the answers likely lie in the magnetic fields of the Sun. These are complex and chaotic, and behave in still poorly understood ways. The brightest gamma rays, researchers note, probably come from magnetic fields deep inside the Sun. Studying them, they hope, could reveal more of what is happening there.
Voyager 2
Operators of the Voyager 2 spacecraft lost contact with the distant probe last month. Human error seems to have been to blame: operators mistakenly sent a command that pointed the spacecraft’s antenna away from Earth. That left it unable to communicate, either by receiving commands or by sending telemetry.
Fortunately satellites and probes are designed to be recovered from such mishaps. In Voyager’s case, the spacecraft periodically resets its attitude, re-aligning its antenna towards the Earth. This should next happen in October, NASA said, meaning communications would be restored by then at the latest.
Yet NASA also attempted to blast the spacecraft with instructions to correct its position. They hoped that the antenna, despite being mispointed, might still pick up enough of a signal to accept the commands. Fortunately this seems to have worked. As of August 4th, NASA confirmed that they once again had full communications with Voyager 2.