The Week in Space and Physics #20
The Week in Space and Physics #20
On extragalactic neutrinos, CAPSTONE and the Lunar Gateway, the aftermath of a rocket impact on the Moon and an asteroid mission delayed
Neutrinos are elusive creatures. Of the trillions that pass through the Earth every day, our detectors pick up a mere handful. Most of those we do find come from nearby places: from the Sun, from the atmosphere or from human technology here on Earth. Yet, every so often, we pick up one or two that came from further afield.
These are the extragalactic neutrinos: particles traveling enormous distances with incredible speed and energy. They come from deep space, from distant galaxies, and are born in some of the most violent events in the cosmos. Perhaps the best known example was the supernova of 1987: an event that occurred just a hundred thousand light years or so away. Astronomers picked up a dozen or so neutrinos coming from it, giving the first hints of what was happening deep in the heart of the dying star.
Since then detectors have found several more such neutrinos. Yet pinpointing where they come from has proven a challenge. Take, for example, a neutrino recorded at the end of May 2020. Astronomers working at the Ice Cube observatory – a neutrino detector based at the South Pole – spotted the neutrino coming from a distant region of space.
Other telescopes then swung into action, scanning the skies for signs of its origin. One galaxy in particular stood out: it had suddenly brightened, before slowly fading away. Observations showed something violent had probably happened, and that this – whatever it was – could have created the neutrino seen on Earth.
More analysis suggested this was a “tidal disruption event”; or, in other words, a star being torn apart by a black hole. At the heart of the galaxy in question is a supermassive black hole. Astronomers think a star ventured too close to the edge of this black hole and, caught in its enormous gravity, was ripped apart.
The arguments in favour of this seem plausible. It, also, matches with past observations of a neutrino coming from a similar event in a nearby galaxy. If so, it is an impressive step: astronomers have only managed to link extragalactic neutrinos to actual events on two or three occasions.
Still, researchers must wait to unlock the full potential of neutrino astronomy. Such a violent event must have spat out enormous numbers of neutrinos, of which billions likely struck the Earth. We picked up just one – which does not give astronomers a lot to work with. To find more we’ll need bigger and better detectors, which, fortunately, engineers are busy designing and building.
That could open up so called “multi-messenger” astronomy, an approach which combines existing light-based measurements with emerging neutrino and gravity-wave astronomy. Both promise to give us a new view of the universe, and, if used together, should help reveal more of its secrets. The age of neutrinos is not yet here, but it is coming.
A Small Step Back to the Moon
On Tuesday last week, NASA made a small step back towards the Moon. The focus of events was Rocket Lab’s Electron, a small rocket that carried an even smaller satellite into orbit. That was CAPSTONE, a twenty-five kilogram probe that will now spend several months voyaging from the Earth to the Moon.
When it arrives, CAPSTONE will enter a never-used before orbit, known as a “near-rectilinear halo orbit”. Unlike many other satellites, which always stay roughly the same height above the Moon or Earth, this orbit dramatically varies in altitude. At its closest point CAPSTONE will be roughly a thousand miles from the lunar surface; at its furthest it will be more than forty-three thousand miles distant.
NASA models suggest this orbit should be stable, lying in a balance between the gravities of the Earth and Moon. It also – since it dips down close to the surface – would allow an ideal staging post for human missions. NASA thus plans to use this orbit for a planned space station, known as the Lunar Gateway. CAPSTONE’s key aim is to prove the orbit behaves as NASA thinks it does.
The Lunar Gateway is envisioned as a small station – nowhere near the size of the International Space Station – locked in a permanent orbit around the Moon. Astronauts visiting the Moon as part of the Artemis Program would use the station as a base, relying on its supplies for extended trips lasting weeks on end.
That is exciting in its own end: no crewed space station has ever been built beyond low Earth orbit. But it would also allow NASA, and other partner nations, to experiment with technologies for building a human presence in deep space. What they learn there could one day be used for missions far beyond Earth: to Mars or even further.
CAPSTONE represents the first small step towards this future. The Gateway itself is still under design, with the first components scheduled for launch no earlier than 2024. Astronauts are unlikely to visit for years – the first mission to the Moon, scheduled for 2025, will skip it entirely, heading straight to the surface. But follow-up flights, if they happen as planned, should see humans enter the station before the end of the decade.
Two Fresh Craters Scar the Moon
Earlier this year, an astronomer tracking the movements of old rocket bodies discovered something interesting. One, his calculations suggested, was on a direct collision course with the Moon. Bill Gray, the astronomer in question, initially thought the rocket was an abandoned SpaceX booster. Later it turned out this was probably wrong and, though debate still continues, it was likely a Chinese rocket instead.
Regardless of whose rocket it was, the impact seemed to happen on schedule. Nobody saw it: the rocket came down on the far side of the Moon, and none of our lunar satellites were in the right place to watch. Still, all signs pointed to an impact, and NASA’s Lunar Reconnaissance Orbiter was directed to photograph the region where it probably happened: the Hertzsprung Crater.
Now those images have been released. As expected, they reveal a fresh crater – but, surprisingly, the satellite also saw another new crater at the same spot. Why the rocket created two craters is unclear – NASA say no previous rocket impacts have done so, but it may be down to the structure of the rocket itself. As for whose rocket it was, no one is yet willing to claim ownership.
Whoever it was, the impact seems to have done little harm. The Moon is a barren place, pockmarked with craters and debris from across the Solar System. Indeed, researchers have deliberately crashed rockets into the Moon before. In 2009 NASA smashed a Centaur rocket into the lunar surface. The resulting debris cloud was monitored by satellites, which later confirmed the presence of water amongst the dust thrown up.
NASA Delays Psyche
Ringing the Sun between Mars and Jupiter is the asteroid belt: a zone of fragmented rock millions of miles wide. One of the largest asteroids there is 16 Psyche, an asteroid one hundred and fifty miles across. It has, so far, been little explored: though NASA plans to send a probe, Psyche, to visit in the next few years.
Psyche will orbit the asteroid for roughly two years, surveying and studying it in great detail. NASA had planned to launch the probe later this year, with the expectation of arriving at the asteroid by 2026. In the end, however, NASA has been forced to delay that date.
According to officials, engineers do not have enough time to complete tests of the onboard software before the target launch date. Rather than risk something going wrong once in space, NASA has therefore decided a launch this year cannot happen. A new date has not yet been announced, though the agency does have several options available over the next few years.