The Week in Space and Physics: Avi Loeb's Interstellar Trash
The Week in Space and Physics: Avi Loeb's Interstellar Trash
On finding alien space trash, magic forms of oxygen, the solar wind and India's latest space telescope
At the time few people noticed the explosion. Partly that was because it happened in the middle of the ocean, far from any inhabited land, and partly because it detonated at three in the morning, when most sensible people were asleep. Military sensors, however, do not sleep, and since they track much of what happens in the Western Pacific, they dutifully noted down the blast.
Because of that, we know a few things for sure. First, the explosion happened at roughly three in the morning, early on January 9th, 2014. Second, it took place at an altitude of eighteen thousand meters, almost twice as high as commercial jets fly; blowing up somewhere to the north-east of Papua New Guinea. And, third, we know it came from a fast moving object, travelling at almost thirty miles a second.
We also know that two other similar events happened in January of that year, once in the mid-Indian Ocean and once over northern Australia. Such events, indeed, are not uncommon. Almost all are meteors smashing into the atmosphere, burning and then exploding when they hit thicker layers of air.
The January 9th meteor, however, was strange enough to draw the attention of Harvard astronomer Avi Loeb. In a paper, he noted that it was one of the fastest meteors ever detected, an oddity that points to an unusual origin for the space rock. Loeb, indeed, argues that such speeds can only be explained if the meteor had entered from interstellar space.
In a letter, the US Government confirmed that claim, saying their analysis showed the object had followed a hyperbolic orbit; one, in other words, that originated beyond the solar system. That makes it an exciting discovery: no other known meteor has been tracked to such an origin.
A few weeks ago Loeb set off in pursuit of this meteor, charting a ship to look for fragments of it on the ocean floor. More dramatically, he claims to have found them, and has since brought up hundreds of small metal spheres from the seabed. These, if he is correct, are the first pieces of interstellar material found by humans.
In a paper he notes that the metal fragments show an unusual composition; one that is not found on Earth, Mars or the Moon. Perhaps, he writes, the meteor came from the crust of a planet around a distant star, or possibly it was forged in the heat of a faraway supernova. In other articles he has hinted at an artificial origin, speculating about alien trash floating through interstellar space.
This is all very exciting. But it is also rather doubtful. Other astronomers have expressed a great deal of scepticism about Loeb’s work. They complain, first of all, that the interstellar origin of the meteor is impossible to verify, since the military will not release the details of their sensors.
Even the metallic spheres found by Loeb seem doubtful. Professor Steve Desch, quoted in New Scientist, says that similar spheres litter the ocean floor. And, with no clear way to measure their age, it seems impossible to confirm they really came from any particular meteor.
This, of course, is not the first time Loeb has made such claims. His earlier work on ‘Oumuamua, the first interstellar comet spotted in the solar system, concluded that it was probably a piece of alien space trash. The rest of the astronomical community disagrees. We lack the evidence to say that, they say, and anyway, simpler explanations can explain what we did see.
The same, they say, is true of this interstellar meteorite. Loeb’s claims are exciting, but they are impossible to verify. Unless he comes up with harder proof - and he is already planning another expedition to retrieve more fragments - his ideas of interstellar trash will remain speculation, at best.
Oxygen: Less Than Magic?
Every atom of oxygen contains eight protons. These are essential to the nature of oxygen - add a proton and you end up with fluorine instead, take one away and you have nitrogen. Protons determine the chemical nature of an atom; by changing the number of protons you radically change its chemical essence.
Ninety-nine percent of oxygen atoms also contain eight neutrons, forming an atom properly known as oxygen-16. Yet a handful contain a different number of neutrons, creating slightly different forms - or isotopes - of the atom. Chemically these are still oxygen - they look much the same, and follow the same reactions - but in terms of nuclear physics they show different properties.
This is most obvious in the stability of the atom. While oxygen isotopes with eight, nine or ten neutrons are stable - fortunately for us - those with six, seven or eleven are not. An oxygen isotope with seven neutrons - one less than normal - will tend to emit a burst of radiation after about two minutes, converting into nitrogen as it does.
The stability of different isotopes is dictated by the strong nuclear force; the force that binds together neutrons and protons in the core of an atom. Give an atom the right number of neutrons and protons and it will be stable; upset that balance and it may disintegrate.
Most stable are the so-called “magic numbers”. When a particle contains a magic number - two, eight, or twenty - of neutrons or protons then it should be unusually stable. Oxygen-16, which contains both eight protons and eight neutrons, is thus considered “doubly magic”, making it extra stable.
Physics predicted therefore, that oxygen-28 - eight protons, twenty neutrons - would be another doubly magic isotope. Yet this was a purely theoretical idea. Oxygen-28 is hard to make, and until recently no experiment had been performed on it.
Recently, however, a team in Japan created atoms of oxygen-28 and looked for the promised stability. Instead they found the atom to be fleeting; disappearing almost as soon as it appeared. Oxygen-28, for all its supposed magic, appears to be highly unstable. A second isotope - oxygen-24 - also seems to break the rules. Earlier experiments found it appeared to be doubly magic when, by rights, it should not be.
All this suggests that something is missing in our theory of the strong nuclear force, especially when we push the limits of the atomic core. Quite what is unclear, but this unexpected discovery could point us towards a better understanding of how atoms behave. Ultimately, that could even give us a clearer view of the fundamental forces of nature.
Probing the Solar Wind
As the Sun closes in on the peak of its eleven year cycle in activity, astronomers are making the most of the opportunity to study our star in detail. Indeed, the past few weeks have seen discoveries related to the origin of the solar wind: the stream of particles that blows outwards from the Sun.
Earlier studies from the Parker Solar Probe, an American spacecraft, had revealed processes that could drive the wind. Now data from the Solar Orbiter, a European observatory, has shown more about how the solar wind is created.
For a long time it has been known that the wind has something to do with coronal holes. In these regions the Sun’s outer atmosphere, the corona, seems to cool and become less dense. Its magnetic properties also change, allowing particles to flow outwards from the Sun, instead of falling back inwards.
After examining one of these coronal holes in detail, the Solar Orbiter spotted “pico-flares” bursting within them. In each a tiny jet of plasma was seen shooting out from the Sun’s surface, releasing a burst of energy that flung particles outwards.
Though each flare was small, astronomers reckon that they are widespread across the Sun. Together, then, they could account for many of the particles we see flowing out from the Sun - and they may, therefore, be the ultimate origin of the solar wind.
India Explores the Sun and the Moon
India, meanwhile, has become the latest nation to send up its own solar observatory. The move comes a week after India landed its first probe on the Moon, and shows the growing intent of the nation to become a serious space power.
The spacecraft, named Aditya-L1, is heading to a Lagrange point situated between the Sun and the Earth. From here, roughly one million miles from home, the telescope will have a clear view of the Sun, one that is never interrupted by the Earth or Moon. Thanks to the unique gravitational properties of such Lagrange points, Aditya will also shadow the Earth as it moves around the Sun. Operators will, therefore, be able to stay in close contact with the telescope.
Aditya is equipped with instruments to study the Sun’s outer layers and to measure the particles it throws out. This, India hopes, will give insight into the particle winds and storms emanating from the Sun; and help us better predict their impact on Earth.