The Week in Space and Physics #19
On the Artemis Program, the elusive tetraneutron, Starlink and astronomy, and the demise of Insight
Getting to the Moon should be easy. After all, we’ve already been - and managed to do it with ancient technology, at least compared to modern smart phones and computers. Last time we tried, in the 1960s, it took less than a decade, all told, to put together a rocket, a lander, a crew of astronauts and a plan. Why, then, is it taking so long this time?
The ambition to return to the Moon has been NASA policy since 2017. The agency, however, has been plotting human flights into deep space – whether the Moon, asteroids or Mars – for far longer. The infrastructure needed, therefore, has been under development since the turn of the century.
At the heart of the new plans is the Space Launch System, or SLS: a rocket that will have the power to blast humans and equipment deep into space. NASA has been working on the SLS since 2011, but no test flight has ever taken place. That should change soon - last week engineers finished a crucial set of tests that pave the way to a lift-off.
The tests aimed to simulate a launch to within ten seconds of an actual lift-off; thereby giving engineers a chance to rehearse almost every step. In the event, however, NASA only managed to get to thirty seconds before liftoff, at which point a leak in a hydrogen feed caused the test to stop.
Despite this, engineers have decided the result is good enough to proceed. Of the more than one hundred functions to test, just thirteen were missed. Most of these, the chief engineer said, have already been tested elsewhere.
That means NASA can shift focus to actually sending the rocket to space. A date for a launch has not yet been announced, but it is likely to happen in the next few months - probably in September or October. NASA has named the launch Artemis I, recognising it as the first step towards an eventual return to the Moon.
On top of the rocket will be an empty Orion capsule. Operators plan to send the capsule towards the Moon, proving its capability to one day ferry astronauts along the same route. After looping around the Moon, Orion will head back to Earth and should, if all goes to plan, splash down in the oceans a few weeks later.
A second flight, Artemis II, will follow eighteen months later. That will see astronauts travel towards the Moon for the first time in five decades, although they will not make a landing. Then, sometime in 2025 or 2026, Artemis III will send the first humans to step foot on the Moon since 1972.
Unlike last time – when the lunar program was abandoned after a few short flights – NASA is planning for a decade or more of lunar exploration. According to leaked documents obtained by Ars Technica, NASA is targeting one lunar mission a year from 2027 onwards.
The first few flights will be dedicated towards building out the Lunar Gateway: a proposed space station orbiting the Moon. Later missions will see more focus on the surface. That should include a rover for astronauts to drive around in and construction of a habitat for longer stays.
Still, the plans may be overambitious. Congress has consistently failed to fund NASA to the level needed for a fast return to the Moon. Instead a slower schedule is more likely, one that will see flights to the Moon every eighteen months or so. That, of course, is if NASA relies on the SLS alone: SpaceX may soon have Starship, a rocket equally capable of reaching into deep space, ready. That will offer more opportunities to explore the Moon, and beyond, if NASA is willing to take them.
Starlink Annoys Astronomers, Again
Astronomers have long regarded Starlink – Elon Musk’s vast satellite constellation – with fear. The satellites are visible through telescopes, smearing streaks of light across sensitive images. As more and more satellites are launched – over two thousand at the last count – the problem grows ever worse.
After concerns were raised in 2019, Starlink fit shades to the satellites, hoping that would make them reflect less sunlight. They helped, to some extent, but recent Starlink satellites seem to have brightened again. That, according to a report in Nature, is because the shades are no longer being installed.
The latest generation of Starlink satellites have lasers for data transmission in space. The shades, it appears, interfered with these links, and so Starlink simply removed them. The company says it is looking into other ways of reducing their brightness, but astronomers seem doubtful a real solution can be found.
Whatever happens, the threat to astronomy is continuing to grow. The Starlink constellation will soon be joined by several others. The number of satellites circling the Earth looks likely to increase by ten-fold or more in the next decade. Astronomers, finally, are starting to fight back. After imploring the United Nations to act, earlier this year they set up a centre to coordinate their activities.
A Sign of the Elusive Tetraneutron?
All atoms on Earth are made of three fundamental particles: protons, neutrons and electrons. Protons and electrons get the most attention. It is thanks to them, and their electric charge, that molecules can form, chemistry can take place and life can exist. Neutrons, by contrast, limit their activities to atoms: they act, in a way, as a glue that binds protons together in the atomic core.
Yet physicists have also long speculated of matter made of neutrons alone. Indeed, certain stars – the neutron stars – should be made of such matter, sometimes called neutronium. Just as atoms can have more or less protons and electrons, researchers believe that neutronium particles could have different numbers of neutrons.
A dineutron, for example, would be a particle made of two neutrons. Back in 2012 physicists actually found such a particle. An atom of beryllium was seen spitting out a pair of neutrons that seem, at least briefly, to have formed a dineutron. Other combinations may be possible. Physicists, however, debate whether collections of three (trineutrons) or four (tetraneutrons) are really stable enough to form.
The first evidence of tetraneutrons, seen two decades ago in European particle experiments, came as a surprise. Physicists had believed that even if tetraneutrons could form, they would be highly unstable: ripping apart almost instantly. Instead the experiments seemed to show the clusters existing slightly longer – a few nanoseconds at best – but long enough to suggest they were a real thing.
Now researchers in Munich have found stronger signs of their presence. An experiment set up to precisely measure the energy of colliding helium atoms found evidence tetraneutrons had formed in the aftermath of the collisions. They don’t seem to have lasted very long – just a fraction of a nanosecond – though that appears to be in agreement with some theories of how they might behave.
More experiments are planned to investigate their presence; experiments that should definitively say if they exist or not. Either way, the results will teach physicists more about the behaviour of neutrons, the forces that govern them and how they might act in the heart of a neutron star.
Insight Approaches The End
After almost four years on the Martian surface, NASA’s Insight probe is close to death. Ever since it first landed, the probe’s solar panels have slowly gathered dust and sand; an accumulation that has steadily reduced the energy they generate. Now, as the Martian winter draws in, power levels are dropping to critical levels.
Unlike other rovers on Mars, Insight is stationary. It was designed to listen for marsquakes shaking the planet and, by monitoring them carefully, to reveal details about Mars’ interior. Over time, however, as energy began to run short, scientists switched off most of the probe’s instruments. Now only one remains: a seismometer recording vibrations rippling across the planet’s surface.
Mission operators had planned to turn this instrument off at the end of June, hoping that by doing so the probe would have enough power to survive until the end of the year. Instead they have now opted to keep the seismometer running: a decision that will see batteries run out in August or September. In exchange, however, scientists should be able to squeeze a bit more data out of the probe.
Typo in tetraneutron article: "Protons and neutrons get the most attention" - I believe you meant "Protons and electrons..."