The Week in Space and Physics
The Week in Space and Physics
On dark matter, Roscosmos and the space station, falling rockets and an unlikely plan for Mars
It was supposed to be boring. Vera Rubin was desperate for that: her Master’s thesis - though later proven correct - had been ridiculed by astronomers. The doctorate, too, was something of a disaster. Her discovery that galaxies grouped together, forming clusters in the void, was shunned for decades by the astronomical community.
In pursuit of something useful but uncontroversial, she turned to the edges of those galaxies; measuring how they moved. This was supposed to be dull work. Galaxies, everyone knew, followed Newton’s laws of gravity. Her work should simply prove, once more, that Newton had been more or less right all along.
Yet Rubin was soon making her most controversial pronouncement of all: galaxies, she declared, were ten times bigger than we could see. Even worse, most of the universe was utterly invisible; missed by almost everyone until her. It was a startling, revolutionary, discovery - and one that astronomers, finally, couldn’t ignore.
The issue lay in the way galaxies spun. Close to their centres they moved as predicted, following the laws of Newton. Yet further out, in those faint edges, they spin too fast, as though some invisible extra mass is pulling them round. Since no astronomer could find this mass, they named it Dark Matter – postulating that a ghostly halo, unseen by telescopes, was surrounding every galaxy.
Over time this idea gained strength. It didn’t just resolve the question of how galaxies spin, but also explained how they clustered together and – perhaps most importantly – how they had formed and evolved over time. Dark matter, astronomers now believe, has played a crucial part in sculpting the modern universe.
And yet, one problem lingers. Vital as dark matter seems to be, we still have almost no idea what it actually is. It seemingly points to a hidden side of the subatomic world; a hint that one – or perhaps many – elemental particles are missing from our knowledge.
XENON1T, an advanced detector, was thus designed to spot traces of dark matter particles crashing into atoms of xenon. Early results, in 2020, seemed promising. The experiment found a sign of unexpected particles moving through it; a faint signal that could, some thought, be the sought dark matter.
But a follow-up experiment, XENONnT, found no trace of this signal. The results, disappointingly, are exactly as standard physics – without dark matter – predicts. Whatever was causing the signal, then, it probably wasn’t dark matter – but something more prosaic, like contamination or simple random fluctuations.
Might we, instead, be able to create dark matter here on Earth? The possibility will soon be tested at the Large Hadron Collider in Switzerland, where physicists have been preparing to collect data looking for dark matter popping out of its energetic collisions.
The experiment will run for several years, until the end of 2025, and look for something known as the dark photon. This particle, if it exists, would show that dark matter exists in a parallel world; interacting through dark forces inaccessible to normal matter. That’s a radical idea: yet, given the long failure to find any trace of the dark stuff, perhaps one worth considering.
Russia and the International Space Station
Will Russia pull out? The question bounced around the world last week, after the head of Russia’s space agency, Roscosmos, announced they would withdraw from the space station program in 2024. Instead, he said, Russia would focus on building their own station, one that could have a militaristic – as well as scientific – purpose.
In truth, Russia has been floating this idea for a long time. The country seems keen to appear uncommitted to the station, a symbol of international cooperation, and its public announcements have often derided the partnership. Yet many of their most controversial announcements came from Dmitry Rogozin, Roscosmos’ director since 2018.
On July 15 Rogozin was abruptly fired from that role, and replaced by Yuri Borisov, an ex-deputy prime minister. When he, speaking publicly with Vladimir Putin, echoed the idea of leaving the station “after 2024”, the media seem to have taken this as an official policy of quick departure.
Yet, as on previous occasions, Russia gave no official notice of withdrawal to its international partners. Oddly, Roscosmos also signed a deal with NASA to send cosmonauts and astronauts to the station until 2025.
In the end Borisov clarified his stance, stressing that Roscosmos intends to continue cooperation beyond 2024. The confusion, he maintained, was down to a mistranslation from Russian; a subtle difference in language missed by foreigners.
Perhaps. In truth, Russia has few other options for its space program. Plans for a new station are unfunded and incomplete. Even if they have the technical capability – which is far from certain – Roscosmos do not have the funding to build one. A new Russian station by 2024 – or by 2030 - is an impossibility.
Russia could turn to China – they, after all, already have a small space station. It is easy to imagine that Russian cosmonauts will soon pay a visit, and perhaps spend some time working on board. But Russia currently owns and operates several modules onboard the ISS. China is not in a position to offer anything remotely similar. For now, whether they like it or not, the International Space Station is the best Russia can do.
China’s Space Station
Out of control rockets plunging towards Earth make for good headlines. China, therefore, has been keeping science journalists busy: several of their rockets have recently fallen Earthwards. One, in 2020, scattered debris over the Ivory Coast, damaging houses but fortunately injuring no one. Another, last weekend, fell over south-east Asia, though mercifully did no damage.
Both incidents involved the Long March 5B rocket, China’s most powerful rocket. Its first stage, a part normally discarded once the rocket reaches orbit, is so large that big chunks can survive re-entry, falling to the Earth’s surface. That, because the stage is discarded at a low altitude, usually happens a few days after launch and, since it cannot be steered, means debris could land almost anywhere on Earth.
Though China argues the risk of harm is low – most of the planet is, after all, ocean – NASA has accused the nation of acting irresponsibly. Other big rockets – like the American Delta IV Heavy – are designed to prevent any big pieces of debris reaching the ground (though, notably, a chunk of a SpaceX capsule recently fell on Australia). For now China has ignored these concerns.
A few more Long March 5Bs are likely to launch soon: China needs them to finish the construction of its Tiangong space station. One new module, named Wentian, docked with the station last week. Another, Mengtian, should follow later this year.
Boots on the Moon… and Bots on Mars?
Could August 29 be the day the SLS finally lifts off? The first launch of NASA’s giant new rocket has been delayed many times before – but now, with all tests complete and final preparations under way, lift-off is starting to look like a real possibility.
The American space agency announced three possible dates for a launch – August 29, September 2 or September 5 – which would see the rocket send the Orion Capsule hurtling towards the Moon. This flight will be unmanned: NASA will need to wait until 2024, at least, before any astronauts ride the SLS into orbit.
Looking further afield, two American companies announced plans to reach Mars by 2024. Relativity Space and Impulse Space, a pair of rocket companies, claim they could put a small probe on the surface of the Red Planet within three years. That, to be blunt, is unrealistic. Neither company has yet put anything at all in space. Mars – in all probability – will have to wait.