The Week in Space and Physics
On muons and volcanoes, the lives of stars, Alpha Centauri and the destruction of Kosmos-1408
You will, I’m sure, be familiar with an x-ray: a high energy form of light that can pass through the human body and therefore – if we use it to take a photograph – reveal our inner forms. This technique works because our bones, organs and skin have different densities; each blocking a different fraction of the x-rays.
An x-ray image of a human thus reveals the varying density of our interiors - and so the shape of our hard bones and soft organs. A similar approach, applied on a far larger scale, can image the insides of structures like mountains, pyramids and volcanoes. Instead of x-rays, however, this technique uses a subatomic particle known as a muon.
Like x-rays, these particles can pass through seemingly solid objects. Muons, however, are much better at doing this - passing through hundreds of meters of rock with ease. Even better, the particles exist naturally - a constant shower of them washes over the Earth, bombarding us from deep space.
Place a muon detector under a mountain, therefore, and you can get an idea of how dense different parts of it are. Harder rocks absorb more muons, and thus show up as darker areas in a muon photograph. Soft rocks, or cavities like caves, rooms or tunnels, show up as brighter areas - something akin to the bones and organs of the mountain.
Famously, this technique was used in 1970 to hunt for hidden chambers in the Egyptian pyramid of Chephren. Though the study concluded there were none, an examination of the Great Pyramid of Giza in 2017 did find a mysterious new chamber - the first such discovery in more than a century. Hints of a corridor running to the chamber were revealed too, though no one has so far ventured inside.
Volcanoes, too, are full of hidden chambers and tunnels. They behave in unpredictable ways, with magma rising, falling and sometimes bursting out in an eruption. Predicting when that might happen is hard - especially as scientists have little idea of what, exactly, is happening inside a volcano.
Some scientists have thus wondered if muons could be used to watch the motion of magma within a volcano. Whether it could, however, was not clear. Muon tracing takes time to perform, time that may not be available in a fast moving eruption. The difference in density between magma and solid rock is, too, small – which can make it hard to pick out in the resulting image.
Nevertheless, a series of studies of volcanoes in Japan, the Caribbean and Italy recently showed that the approach has promise. Images of the interior of Mt Etna, in Sicily, for example, showed that a cavity was forming, probably due to blasts of hot gases. A few weeks later that part of the volcano collapsed – an event that we may, in future, be able to predict.
Though that’s not quite as good as predicting an eruption in real time, it is a tool that could help us monitor dangerous volcanoes. Volcanologists should be able to combine muon imaging with other approaches - such as tracking gas levels or earthquakes - to improve our knowledge of a volcano on the edge of an eruption.
The approach is not, however, always practical. The detectors are expensive, for one thing, and must be placed close to the volcano. For those underwater, or in remote areas, that may be hard - or even impossible - to achieve. That, for now at least, probably limits muon imaging to the most dangerous and active volcanoes.
Still, for those volcanoes, the knowledge imparted by the invisible rain of muons will be invaluable. The ability to peer inside the beating heart of a volcano, to watch as magma rises and falls, as cavities form and collapse, will reveal one of nature’s most violent processes - and may one day save millions of lives.
The Science of the James Webb: Stars and Dwarves
The launch of the James Webb Space Telescope was slightly delayed this week. It should now take place on December 22. Such delays are common in the tricky rocket business, especially when dealing with a payload as fragile and important as the James Webb.
Over the past few weeks we looked at the early universe, the birth of stars and galaxies, and saw how the James Webb will give us a new view of that long ago era. Its powerful eye will, however, also spend time looking at the closer universe: spying out nearby stars and planets.
Astronomy, thanks to telescopes like Hubble, can tell us a great detail about how stars are born, live and die. We’ve seen stars of many kinds - from faint red dwarves to supermassive giants - and watched them evolve from bright young stars into fading white dwarves. Yet some areas of their lives remain shrouded - literally - in mystery.
Stars are born in clouds of dust and gas, often when passing shockwaves – perhaps from a nearby supernova – disturb those clouds enough to trigger nuclear reactions. Peering through that dust is almost impossible for our existing telescopes. That means capturing a star, or a solar system, in the moment of birth has so far eluded astronomers.
The James Webb, however, will watch the sky in infrared radiation. That, researchers hope, will allow it to see through the dust clouds and seek out the heat of newly forming stars. That should reveal the exact processes that ignite stars and shed light on how planets and solar systems form. Ultimately, that could answer questions about the birth of our own solar system.
There are, too, strange objects that seem to float between the level of stars and planets. These – the brown dwarves – are a dozen or more times bigger than Jupiter, but are still too small to sustain the nuclear reactions that power a star. Billions probably litter the galaxy, but since they aren’t bright enough to easily see, we only know of a few hundred.
Thanks to radioactive decay and some small scale nuclear activity, brown dwarves should be hot – even if they don’t emit much light. That makes them ideal objects for a telescope like the James Webb to seek out. In doing so the telescope should reveal a mysterious class of cosmic object – and perhaps help redefine the line between planet and star.
The Toliman Telescope
Centuries ago Arab astronomers named Alpha Centauri – the closest star system to the Sun – Al-Thaliman, or, in English, the two ostriches. The name made its way into Europe as Toliman, eventually coming to refer to only one of the three stars we now know make up the Alpha Centauri system.
Today those stars are more coldly known as Alpha Centauri A, B and C, though they remain objects of fascination for astronomers. They lie roughly four light years from us, the closest stars – other than the Sun – in the sky. Alpha Centauri C – the smallest and closest – almost certainly has a planet. Given the violent nature of that small star, however, it is equally certainly uninhabitable.
Alpha Centauri B and C are more stable and Sun-like, but astronomers have never seen any planets around them. Now, however, a privately funded team hopes to change that. They are building a small satellite, called – after the ancient name of Alpha Centauri – Toliman, which will watch the twin stars.
If a planet is in the system, it should create a slight wobble in the stars’ movements – a consequence of an additional gravitational pull on them. Toliman should be sensitive enough to pick up this wobble, and thus – the team hope – confirm, or not, if any planets circle the two stars.
Russia Blows Up a Satellite
Early last Monday morning, a Russian missile streaked skyward from the Arkhangelsk Oblast; a far northern region close to Finland. As it did, a long failed Soviet satellite was passing almost directly overhead. That satellite – Kosmos 1408 – it turned out, was the target of the missile. A few minutes later it was destroyed; shattered into over a thousand fragments.
This is not the first time a superpower has destroyed an orbiting satellite. The capability has been demonstrated by the United States, China and India in the past. But such tests are risky. They generate large amounts of space debris, turning a single large object into hundreds or thousands of smaller ones.
At orbital velocities, each small piece of debris is dangerous; a destructive and long lasting piece of shrapnel than can devastate a satellite. Adding hundreds more into a crowded orbit – as the Russian test did – is an uncooperative act, making space harder and more dangerous for everyone.
Russia’s test was foolish, dangerous and hard to understand. Anti-satellite tests should – if they must be done at all – target low flying satellites, ones where the debris produced will burn up in months, not years.
If you enjoyed this post and haven’t subscribed already, then why not subscribe to our One Blue Planet newsletter or share it with a friend? If you subscribe, you’ll get two free emails a week covering the latest news and findings from physics, astronomy and the space industry.