When it comes to elephants in the room, the sun’s a doozy. It’s enormous; it’s immensely powerful – but we know next to nothing about it. And the best science has to offer hasn’t even scratched the surface.
Our sun is getting moody. Large solar flares are being flung into space frequently. Current sunspot counts are far above official expectations.
At the time of writing, the sunspot activity score was 80. But the anticipated peak of solar activity – expected to be in July 2025 – usually averages a score of 179.
Such an early surge could mean an unexpectedly strong activity cycle. Or it could just be one of those seasons that gets off to an early start.
“We’re about as good at predicting the Sun as my being able to tell you what the Tattslotto numbers will be tomorrow,” says University of Tasmania astrophysicist Dr Marc Duldig. “It’s as much guesswork as anything else.”
And that’s a problem when it comes to the hordes of satellites now circling the Earth, not to mention the astronauts, aircraft, masses of cable and rail networks, personal electronics… it’s the proverbial elephant in the room.
After all, the Sun accounts for 99.8% of our solar system’s mass. So, when it sneezes, its closest neighbours can catch more than just a cold. And our sun’s having a bit of a fit at the moment.
As if to emphasise the point, on 25 April spaceweather.com reported that Sunspot AR2993 erupted twice in quick succession, producing an overlapping pair of M1-class solar flares. The double-whammy blast caused a minor “albeit long-lasting” radio blackout over Southeast Asia and Australia, affecting frequencies below 20 MHz.
It’s early days in this active phase of the Sun’s roughly 22-year solar cycle, also known as the solar magnetic activity cycle. About every 11 years, the Sun’s magnetic poles “flip”, and when that happens, its coronal skin breaks out in spots.
We’ve been watching this process since 1755; it’s said to be the longest continuously recorded cycle of any natural phenomena. The current one is solar cycle 25 – the 25th such cycle observed since 1755.
We don’t know why it happens, Duldig says. But we’re getting a grasp on how.
This time around, NASA’s Parker Solar Probe and Europe’s Solar Orbiter are getting up close and personal for a more detailed look. Their early results are spectacular; their observations of the Sun’s activity exceed all expectations.
But we still don’t know what’s going on.
A star to sail by…
Navigating the solar system’s storms and shoals is a pressing issue. Out in space, as down here, the Sun is in control. And it wields a two-edged sword.
For example, it can protect us from the most powerful objects in the known universe – cosmic rays. When accelerated to the fastest observed levels, these particles are almost travelling at the speed of light.
To put it in context, says Duldig, that’s the equivalent force of a tennis ball hit hard enough to travel at 100km/h … condensed down to the point of a single proton.
But the sun’s protection is not consistent.
The intensity of solar wind pushing against these rays depends on the 11-year cycle. And the 22-year north-south-north pole switch determines how the magnetic field is oriented towards the galactic background. That’s the kind of thing you need to know if you’re packed into a tin can headed towards Mars, says Duldig. It will determine how much shielding astronauts will have to carry with them.
“My personal feeling is that the best time to go is sometime during the rising phase, like now, as you have less coronal mass ejections carrying the kind of particles that would be dangerous to astronauts,” Duldig says.
The rising phase tends to produce more and more sunspots quite quickly. But those regions don’t have as many eruptions. “Most of the activity from the Sun, when we get more auroras and solar storms that hit the Earth, is actually in the top part of the declining phase of each cycle,” Duldig says.
In terms of cycle 25, that would be in the years immediately after 2025. Elon Musk hopes to launch his Mars mission in 2029.
He will have to watch the solar weather closely, says Duldig. And he certainly shouldn’t trust any forecasts. “We’re not going to understand the sun’s dynamo mechanism anywhere near enough for that to happen, say, within the next 50 years – unless there’s some fantastic breakthrough,” he warns.
Engine of life
We haven’t even scratched the surface when it comes to comprehending our resident star, although we have ideas.
“There are many theories – nearly as many as there are theoreticians,” Duldig says.
In fact, about 20 different models attempt to explain the Sun’s mechanics. We don’t yet know enough to eliminate any of them. We know the sun is fuelled by nuclear fusion; we know that less than 0.001% of that energy is what powers the heat contained in the corona.
The corona’s where the wild plasma flows. The ultra-hot, ionised gas is made up of free ions and electrons. It has physical properties similar to water or any other fluid – making it very difficult to predict.
But it gets even more complicated. Plasma particles are electrically charged. Myriad magnetic fields exert force on the plasma fluids. And the electric currents of the plasma – in turn – distort the magnetic fields. It’s a boiling cauldron of particle motion, electric flows and magnetic force.
Little wonder astronomers are so confused.
It’s also why the world doesn’t yet have enough computing power to calculate a climate model of the Sun at sufficiently high resolution and scale. At the moment, Duldig says, the best we can do is improve how quickly we can learn about a solar event once it happens.
“One of the big tasks we face is remote sensing – through many different techniques – what’s going on as these things propagate from the Sun towards the Earth,” he says. “That way, we can have a much better handle on what we need to do to mitigate its impact.”
For example, when a solar storm hits the most significant concern as far as Earth is concerned is whether the storm front’s magnetic field is pointing north or south. When it’s pointing south, that’s when we get the biggest compressions and changes in the Earth’s defensive magnetic field.
“That’s not easy to measure at a distance,” Duldig says. “And the storm can twist as it moves. So we often only get an idea of what’s going to hit us an hour or so beforehand.”
And that’s all thanks to a strategically positioned satellite flashing reports of what’s rushing past.
As for solar cycle 25, Duldig says that it’s likely to be middling in its intensity.
“I don’t think it will be too bad,” he says. “Four out of the past seven cycles will have been bigger than this one. But that’s not to say you can’t have one spectacular event come out of it.”
Jamie Seidel is a freelance journalist based in Adelaide.