The Week in Space and Physics: Solar Storms
On tree rings and solar storms, the death of Mars, Ryugu and a strange star
In early October the Sun erupted. Moments later, as waves of radiation swept over the Earth, radio signals across the Americas were knocked out; a brief sign of the incoming storm. Power grids soon took action, protecting critical equipment from the wild magnetic fluctuations racing towards the Earth. Astronauts, perilously exposed to the radiation, took shelter onboard the Space Station.
Remarkably the flare also left a slight trace in the Earth’s biology. As it washed over the planet, it created a burst of radioactive carbon-14 atoms in the upper atmosphere. Over time those atoms will drift towards the surface, where they will eventually be absorbed by plants and trees. They will thus find their way into tree rings: leaving a faint but measurable fingerprint in every forest on Earth.
Analysis of this tree ring record, which stretches back thousands of years, has revealed some intriguing events. Two unusually big spikes of carbon-14 appear in 774 and 993 AD. Other, similar spikes, reoccur in older trees; events that hint at rare but powerful waves of radiation sweeping the planet. These surges – known as Miyake events – may be caused by massive solar flares, far larger than anything we have ever seen.
Yet a closer study of them, reported in the Proceedings of the Royal Society, suggests otherwise. While solar flares are relatively brief – lasting a few hours or days at most – these events seem to have lasted for years at a time. There also appears to be no link between their timing and the solar cycle – a regular pattern in the intensity of the Sun’s activity.
Solar flares are not the only explanation for Miyake events. But most of the other contenders are also brief in nature. A gamma ray burst, for example, would produce a sudden sharp burst of radiation, but is unlikely to last for more than a few days. Supernovae are a possibility, but other studies have found no rises in carbon-14 matching known supernova, as might be expected.
Possibly, then, the events are linked to other things happening on the Sun. Its magnetic field – which drives solar flares – has been known to weaken and strengthen over long periods of time. Something like this could have produced the Miyake events in the carbon-14 record; though exactly how is not at all clear.
Still, if the Miyake events are not massive solar flares that is good news for us. Observations of other sun-like stars have shown some with huge flares, so powerful they would devastate our technological civilization. Whether our own star is capable of the same is an open question: one that further study of the Miyake events will hopefully resolve.
How Life on Mars Wiped Itself Out
Life on Earth once came close to wiping itself out. Roughly two billion years ago, as ancient bacteria began to colonise the oceans, they pumped out vast amounts of toxic oxygen. Toxic, that is, because primitive life evolved in the absence of oxygen, and its sudden presence acted much like a poison.
The result – sometimes known as the Oxygen Catastrophe – was a sudden mass extinction of life. After, as the planet cooled, the same surge of oxygen triggered a series of ice ages and, much later, created the oxygen-rich air we breathe today.
A new study of Mars suggests something similar could once have happened there. If Mars was long-ago habitable, as seems ever more likely, then bacteria-like creatures may have lived on or below the surface. As on the early Earth, those creatures would have lived under an atmosphere full of carbon dioxide and hydrogen. That should have warmed Mars enough for them to thrive.
Yet, according to the analysis, this life would have given off methane as a waste product. That would have altered the atmosphere: removing hydrogen and replacing it with methane. The result, like on Earth, would have been a catastrophe.
The changing atmosphere would have cooled the planet drastically. The warm conditions that allowed life to thrive would have ended: and, as a result, a mass extinction would have followed. The researchers speculate that some bacteria could have retreated deep into the crust of Mars, where warmer conditions may have allowed it to hang on. If so, traces of this life might still be present, waiting for us to find them.
In a related study, other researchers uncovered strong evidence of ancient Martian oceans and rivers. By employing techniques used on Earth to measure changes in water systems, they found signs of long dry river beds and ocean shorelines. What’s more, the pattern of rocks and ridges suggests that those ancient oceans were rapidly changing: rising and falling with a fast tempo.
That, then, both supports the idea that Mars once had life, and provides a plausible explanation for what might have happened to it. The search must now move to Mars itself; where traces of that life – if it really existed – should linger in its rocks.
Hayabusa Reveals the Story of Ryugu
Back in 2018 a Japanese spacecraft, Hayabusa2, visited the asteroid Ryugu. Two years later, after a long voyage back to Earth, Hayabusa2 fired a capsule deep into the Australian desert. Inside were pristine rocks captured from the asteroid; a sample that researchers hoped would shed light on the early Solar System.
That hope reflects the long life of asteroids like Ryugu. Theory suggests they are ancient objects, leftovers from the cloud of dust and gas that created the planets. They should, therefore, reflect the conditions of the early solar system.
Evidence from Hayabusa2’s samples supports this idea. Ryugu, researchers have found, was once part of a far larger asteroid that formed in the outer reaches of the solar system. Yet at some point that asteroid collided with another and shattered. Some of those fragments later seem to have come together to form Ryugu.
Intriguingly the rock samples contain gases and even small diamonds that are far older than the solar system itself. These likely formed around dying giant stars and in the heat of supernova, before somehow ending up close to the cloud of gas and debris the solar system emerged from.
Sometime relatively recently, however, Ryugu seems to have undergone a sudden transformation. After billions of years lying far beyond Pluto, around five million years ago it began the long journey to the inner solar system. Why is unclear – perhaps a passing star pushed it inwards or a close encounter with another asteroid flung it onto a new course. Either way, Ryugu has ever since remained between Venus and Jupiter: a perfect target for the inquisitive creatures on the third rock from the Sun.
Is This Strange Star a Strange Star?
Neutron stars are some of the oddest things in the universe. They form when a massive star collapses, imploding with such force that the atoms themselves are crushed. Electrons and protons are forced together, producing a neutron core of incredible density.
This physics of this core stretch our theories to a breaking point. Equations struggle to explain exactly what happens to neutrons in such extreme conditions. Some physicists speculate that quarks – the fundamental components of neutrons – might themselves begin to break down. This, theoretically, could form something known as a quark star – or, in the most extreme case, a “strange star”.
All this is very theoretical. But recently astronomers have spotted a star far too small and light to be a normal neutron star; yet equally too dense to be anything else. Could this be, as some are suggesting, be the theoretical strange star? For now the evidence is weak, but the idea is certainly interesting, and well worth further study.
It's so refreshing to read about subjects that fascinate me and feel like I'm reading a great science fiction novel. Thanks for writing these articles!