The Week in Space and Physics: The Unnatural Elements
The Week in Space and Physics: The Unnatural Elements
On elements beyond uranium, the world's largest fusion reactor, space planes and a problem with Voyager
For a long time, the periodic table ended at element number ninety-two. In prime place, of course, stood hydrogen, the lightest of all the atoms. Then came helium, and lithium, and - barring a few gaps - all the rest up to uranium, the ninety-second and last known element.
Beyond that the table was left empty. Possibly, scientists at the time thought, more elements would turn up, hidden in obscure rocks or revealed - like helium was - in patterns of starlight. Yet as time went on, and scientists grew tired of searching rocks and stars, they concluded that uranium was the limit. No elements existed beyond that point, at least, not in nature.
In the 1940s, however, as men and women began to bombard atoms with neutrons, they started to add new elements. The first to come was Neptunium, discovered in California in 1940. Then came Plutonium - put to use, of course, to build the atomic bombs used in the Trinity test and later over Nagasaki.
From the debris of those bombs came even heavier elements, from Americium - element ninety-five - to Fermium - element one hundred. A handful of extra elements, stretching all the way up to number one hundred and eighteen, have since been made in particle colliders. Few of these last for long. The heaviest now known, Oganesson, exists for a fraction of a second before breaking apart.
This illustrates the problem with the elements that lie beyond uranium. All are unstable, easily breaking apart into lighter atoms. The average atom of Neptunium, for example, exists for only a few centuries before it breaks apart; those of Fermium survive for less than a year. Even if any of those elements were present on the Earth when it formed, then, they could not have survived to the modern day.
Possibly, however, they are still being made in violent supernova explosions or in neutron star collisions. Researchers think most elements heavier than iron formed in this way, and there is no obvious reason why the process would stop with uranium. Indeed, in a recent survey of around forty stars in our galaxy, astronomers reported signs that such heavy atoms were indeed made.
Inside those stars they found four elements, stretching from ruthenium to silver, that matched with another set of elements known as lanthanides. Such pairings often result from nuclear fission - the process by which heavy atoms like plutonium split apart. Their presence in these stars, therefore, hints that fission was once happening. Based on their masses, it seems to have involved elements heavier than uranium.
This, of course, is not a direct proof that such atoms really exist. But it is an intriguing hint that such heavy atoms can form naturally, and, perhaps, are not just confined to the insides of particle colliders, or to the aftermath of an atomic explosion.
The World’s Largest Fusion Reactor
Following a test run at the end of October, the European Union and Japan opened the world’s largest nuclear fusion reactor. The facility, located north of Tokyo, will heat hydrogen to temperatures of two hundred million degrees celsius. That is hot enough to briefly sustain fusion reactions.
The ultimate goal of such reactors, of course, is to produce electricity for widespread use. In theory fusion is ideal for this - it is far safer than nuclear fission, produces little pollution and uses an abundant and widespread fuel source. In practice, however, controlled fusion has proven rather hard. For it to work, hydrogen atoms must first be heated to enormous temperatures. Even then, the resulting plasma must be carefully controlled to sustain the reaction.
At present physicists are pursuing two main ways to do this. One, which uses lasers to squeeze pellets of hydrogen, is being developed with some success in America. The other, which uses magnetic fields to control the plasma, is the subject of an international project known as ITER.
The new facility in Japan forms part of that project. Researchers plan to use the reactor to test techniques for controlling plasma; work that should pave the way to an even bigger facility. That reactor, currently being built in the south of France, will be the first fusion reactor to regularly output more energy than it takes in.
If that can be done successfully, it would unlock the way to using fusion as a reliable source of electricity. European plans call for ITER to be followed by DEMO, a reactor able to generate hundreds of megawatts of electricity - enough to power a small city. If things go well, DEMO could be built by the 2050s.
Whether that will really happen, however, is hard to say. The French reactor was supposed to be ready by 2025, yet reports suggest this will be delayed by at least three years. Its most important experiments – those fusing the hydrogen isotopes of deuterium and tritium – will take at least a decade longer to begin. Despite the news from Japan, the age of nuclear fusion still seems to be decades from reality.
A Tale of Two Space Planes
Two of the world’s most advanced and secretive space planes look likely to return to orbit in the next few weeks. Indeed one, owned by China, is already back in space - having lifted off from the Gobi Desert last Thursday.
The other, operated by the US Space Force, was scheduled to launch earlier in December. Problems - exactly what is unclear - delayed that, however, and lift-off will probably now take place towards the end of the month instead.
Both China and America keep the details of their space planes secret. We do know, though, that both are automatic, capable of guiding themselves back down to Earth without astronauts onboard. Both also seem to be capable of spending years in orbit, during which they conduct mysterious experiments.
Past hints suggest they are used to test emerging technologies in space, including experiments with new materials that might prove useful for spy satellites. They likely also have the ability to interact with objects already in orbit. Potentially that could allow them to examine and interfere with hostile satellites.
It is possible, some observers think, that America’s space plane could be heading to a higher orbit than normal this time. The plane will be launched on top of SpaceX’s Falcon Heavy rocket; a launcher capable of sending the space plane to an orbit tens of thousands of miles high. That, if it happens, would be breaking new ground for the mysterious spacecraft.
A Faulty Voyager
Something seems to have gone wrong with Voyager I, one of the most distant spacecraft from Earth. According to NASA, a fault on one of the probe’s computers means Voyager is currently unable to send scientific or engineering data back to Earth. They seem confident, however, that the spacecraft is still able to receive and execute commands sent by controllers.
The problem seems to lie in Voyager’s flight data system, a module responsible for collecting data from the spacecraft’s subsystems. Rather than sending useful data, though, the system recently started sending a repeating sequence of ones and zeros. That has left NASA unable to monitor the health of spacecraft systems or to use Voyager’s scientific instruments.
NASA engineers first tried the obvious solution - turning the affected system off and on again - but the strange behaviour still continued. Instead engineers will need to examine Voyager’s decades old manuals in the hope of finding a fix. That, NASA said, could take weeks to complete.