The Week in Space and Physics
On the quasi-moon Kamo'oalewa, the first galaxies, high speed dust and the next Moon landings
It’s not, normally, the kind of thing that attracts much attention. A few million miles from Earth lies a small red rock, roughly forty meters across, tumbling gently around the Sun. Astronomers, you might think, would have more interesting things to look at.
And yet the astronomical world is strangely interested by this rock. Telescopes spend days trained on it, watching its every twist and turn. Space agencies are busy planning missions to visit it and designing probes to descend to its surface before bringing bits of it back home.
That’s because Kamo’oalewa, as the rock is known, occupies a special and almost unique status. Kamo’oalewa is a “quasi-moon”, an object that technically orbits the Sun but spends much of its time close to the Earth. Five such quasi-moons are known, and Kamo’oalewa happens to be the closest and most stable of them.
Astronomers first spotted it in 2016, using a telescope in Hawaii, and soon realised that Kamo’oalewa always hovers just in front or just behind our planet. For most quasi-moons this is a temporary arrangement. They spend just a few years or decades close to Earth, before drifting away into the depths of space.
Kamo’oalewa, however, will hang around our planet for centuries. Though its distance - usually a few million miles from Earth - makes it very faint, it happens to be ideally placed for observations every year in April. Astronomers thus undertook detailed measurements of the rock in 2017. The results of that study, published this month, show some interesting findings.
It, they found, appears far redder than most asteroids lingering close to Earth. Since most of those asteroids have a common origin – formed in the early days of the Solar System – Kamo’oalewa’s odd colour suggests that it was actually formed in a different fashion, or, maybe, came by chance from somewhere else.
One possibility is a cloud of asteroids following the Earth, of which Kamo’oalewa is the only one we’ve so far seen. Astronomers know that such clouds follow some of the other planets in our solar system – especially Jupiter – but have never seen signs of one close to Earth. Further surveys of the sky should soon reveal the cloud, if it really exists.
The team notes, however, that the rock’s colour seems to match with a piece of the Moon brought back by Apollo astronauts. That hints at a more intriguing explanation: Kamo’oalewa may once have been part of the Moon, until it was – perhaps in a powerful impact – blasted off the surface and into its current orbit.
Kamo’oalewa’s unusual orbit strengthens that idea. Unlike other asteroids, Kamo’oalewa moves slowly when it is close to the Earth and Moon, a sign that it could share a common origin. How recently it could have formed, however, is not clear – though calculations suggest its current orbit should only have been stable for around a century.
Astronomers will soon get an even closer look at Kamo’oalewa. In the next few years a Chinese mission, ZhengHe, is expected to travel out to the asteroid, grab a piece of it, and then return it to Earth. That will allow astronomers to precisely study its rocks and – hopefully – to confirm whether Kamo’oalewa really was once part of the Moon.
The Science of the James Webb: The First Galaxies
Last week’s newsletter covered the Epoch of Reionization, a long sought era in which the first stars flickered into existence. The James Webb Space Telescope - to be launched in December - could give astronomers their first glimpse of those primordial stars. But it could also show them something far bigger: the birth of the first galaxies.
Cosmologists think the seeds of those galaxies were sown in the Big Bang. Though matter was spread almost perfectly evenly across the cosmos, random quantum fluctuations created some regions where matter was slightly denser and others where it was slightly thinner. Gravity, acting over millions of years, tended to pool matter in the denser regions. That eventually created vast clouds of gas - and equally enormous voids.
Observations of the Cosmic Microwave Background - the earliest relic we have from the universe’s past - show, however, a flaw in this theory. The fluctuations in visible matter - the kind that makes up stars and planets - are simply too small to explain how galaxies formed.
Only by adding in a lot of invisible matter - call it dark matter - can cosmologists make the numbers add up. Fortunately, however, the amount of dark matter needed to explain the early universe matches quite with the amount astronomers think must be present now, in order to explain how galaxies spin.
This is a good sign that dark matter is actually something real - and a fact that alternative theories of the missing matter struggle to explain. If cosmologists are right, then dark matter played a crucial role in the history of the universe: acting as the threads around which galaxies, and later stars, were spun.
That, though, should have happened slowly. Indeed, at the beginning there may not have been many galaxies at all. Instead the cosmos was scattered with smaller structures, known as protogalaxies. Each contained no more than a few thousand of stars. Over time, thanks to gravity, these protogalaxies collided and merged, building the galaxies we see today.
Unfortunately, much of this is speculation based on computer models. Indeed, those models have some major problems: astronomers cannot explain the variety of galaxies we see, nor why they spin as fast as they do. That hints that something is going on that we don’t fully understand, or haven’t accounted for in our models.
The James Webb should, for the first time, be able to see light from those protogalaxies. That should help astronomers work out the kinks in their models, and - if there are no big surprises - perhaps shed more light on the mystery of dark matter.
Encounters with Cosmic Dust
When the Parker Solar Probe approached the Sun in April this year, it reached the astonishing speed of 150 kilometres per second. That – the fastest speed ever achieved by a manmade object – would be enough to cross the Atlantic in twenty seconds, and then to loop around the entire planet less than five minutes later.
Such speeds, naturally, bring challenges. One of the biggest is the problem of interplanetary dust – a fine residue from passing asteroids and comets scattered across the Solar System. Though these dust grains are typically tiny, just a fraction of a millimetre across, at high speeds they act as a kind of hail, constantly impacting on a spacecraft.
Each impact, indeed, releases enough energy to completely vaporise the dust grain, creating plasma - an extreme form of matter. That eats away at the surface of spacecraft, gradually eroding protective layers and even – if the dust grain is big enough – causing damage to vital components.
Researchers have now picked up signs of these impacts on the Parker Solar Probe. Some photographs taken by the spacecrafy show streaks - signs, they think, of larger impacts tearing shreds of metal away from the spacecraft. Magnetic sensors, too, picked up slight disturbances, evidence of plasmas forming around the probe.
These impacts seem to happen more often than predicted. That suggests there is more dust than we thought – but on average each impacts is smaller than expected. That, overall, is good news for the Parker: researchers think it will easily withstand the collisions for years to come.
Eventually, however, the spacecraft will meet a dust grain that deals it a fatal blow. Its cooling system, perhaps, will rupture - and that, under the full heat of the Sun, will mean certain destruction. The Parker Solar Probe, after a decade or more of service, will be turned to dust itself; fated to linger on for millennia more.
NASA Delays the Moon Landing
The return to the Moon is, once again, delayed. NASA last week admitted defeat in their effort to land a crew of astronauts on the lunar surface by 2024. They now say the mission can now take place no earlier than 2025.
This outcome has long been inevitable. NASA does not have spacesuits ready for the astronauts, it does not have a lunar lander, and - worst of all - it does not have a rocket to carry them there. Many reasons are to blame: a lack of funding is the most crucial, but the pandemic and lawsuits have also slowed work.
A landing in 2025 still looks, quite frankly, unrealistic. NASA hinted at this by saying the year is no longer the target date, but rather a “no earlier than” date. In other words: NASA will only land on the Moon in 2025 if everything from now on goes perfectly. That is all but impossible.
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