Most of us are probably aware of the Sun’s magnetic cycle, rising and falling through a period of some 11 years. When this cycle is at its peak – or solar maximum – the surface of the Sun literally broils with sunspots which can sit on their own or as clusters. These sunspots range in size, with the largest thus far recorded measuring over 299,000 kilometres across – large enough to swallow two Jupiter-sized planets side-by-side! The sunspots are accompanied by an increase in solar flares and coronal mass ejections (CMEs) bursting away from the Sun and its corona.
At their most violent, flares and CMEs are fully capable of knocking out satellite systems, completely overwhelming critical GPS and direct communications systems and even bring down power grids if we happen to be in the path of one. Such periods of solar maximum can also see the Sun’s magnetic field flip entirely, before returning to “normal” after two further cycles (referred to as the Hale Cycle). By contrast, periods of solar minimum saw the Sun far quieter and less prone to fits of stormy anger.
Because of the Sun’s ability to be so disruptive, understanding how it behaves and learning to understand what we are seeing as a solar cycle progresses is becoming increasingly critical to maintaining our civilisation’s ability to function. Take GPS systems for instance. Whilst the help guide us when travelling, the signals they output play a critical role in things like the operation of power grids and oil rigs – and even financial systems and services. So a CME overwhelming a system like Galileo or GPS could do far more than just inconveniencing a trip to granny’s new house…
Thus, observations of the Sun from the surface of the Earth, of local orbit and from deep space – including fairly up close and personal to the Sun with missions such as the Parker Solar Probe – has become an essential element in maintaining much of the technology on which we depend. However, we’re not just observing the Sun visually: for the last 40 years we’ve been listening to it as well; in doing so scientists have found that something quite unexpected is going on inside the Sun.
Since 1987 a team of scientists based out of the University of Birmingham in the UK have been operating a series of specialist observatories located in the Americas (California and Chile), Europe (Spain), South Africa and Australia (Western Australia and New South Wales). Across 40 years, the network – called BiSON (Birmingham Solar Oscillations Network) – has been listening to the Sun’s “heartbeat”, oscillations within the Sun caused by sounds generated inside the Sun’s churning innards and which bounce around through the various layers. These oscillations can actually reveal much about what is going on within the Sun in a science called helioseismology. And what BiSON has discovered is twofold.
The first has been that, contrary to expectations, the period of solar minimum in a cycle is significantly different to the last, and that far from being a calm interregnum between the more violent peaks of the Sun’s cycles, each period of solar minimum carries within it indicators of just how violent the next period of solar maximum is likely to be – at least, to a point.
The second finding is more confusing. The majority of the Sun’s magnetic activity occurs within a layer below its surface – and throughout the period of listening by BiSON, this layer has been growing increasingly shallow, effectively squeezing the Sun’s magnetic activity into a smaller and smaller area. In theory, this squeezing should result in the Sun’s magnetic activity becoming more energetic and the periods of solar maximum more violent; but that’s not the case. Instead, two things are happening.
The first is that the most recent periods of solar maximum have been exactly as the preceding periods of solar minimum indicated: cycle 24 was a lot calmer than either cycle 23 and cycle 22. Likewise the period of solar minimum between cycle 24 and cycle 25 indicated the latter would be mild as well – and by-and-large it has been. However, in contrast to this, the BiSON data reveals the subsurface magnetic activity and its associated oscillations within the Sun’s layers during the solar maximums for cycles 24 and 25 have been every bit as powerful as recorded for cycles 22 and 23. Thus, it is like the Sun is seething with rage inside itself – but is showing no outward sign of that rage other than a handful of extremely power outbursts (which, as note, are to be expected during periods of solar maximum).
No-one is sure why either the squeezing of the magnetic activity layer within the Sun is occurring or why the measurements of the Sun’s oscillations appear to be so at odds with the levels of behaviour seen during the recent periods of solar maximum. Potentially, it might simply be we’re catching sight of a much longer cycle in the Sun’s behaviour in which the area of magnetic activity is periodically squeezed before gradually being allowed to “expand” again. However, it might also signify a much deeper change in the Sun’s behaviour which could result in a much greater shift in its fundamental character which could come to have a significant impact on our reliance on space-based technologies simply because such a shift could undo much of what we’ve learned about the Sun and make it harder to predict its future behaviour.
At the same time as the BiSON released its findings, another study published its review on a solar event which might possibly indicate other changes might be taking place in and around the Sun – although in this particular instance it is far to early to draw any definitive conclusion.
As well as giving rise to solar flares and CMEs, periods of solar maximum tend to see an increase in large-scale radio bursts from the Sun. These come in a variety of types, one of the more powerful of which is the Type IV. These radio bursts have a broader spectrum band compared to other types, crossing multiple MHz and GHz frequencies. They can also last for longer – from several hours to a few days and can be a precursor warning for a CME. In August 2025, as cycle 25 was well on its way to the peak of its solar maximum period, the Sun let go of a type IV radio burst that lasted not for hours or a few days – but for almost three weeks. That’s four times longer than any other Type IV burst from the Sun ever recorded.
Such was its duration, the burst was recorded repeatedly by four separate space observatories watching the Sun from different locations. These comprised NASA’s STEREO-A, occupying a heliocentric orbit just inside that of Earth’s own orbit around the Sun; the Parker Solar Probe, also in orbit around the Sun, but practically right up in the Sun’s face; the Global Geospace Science Wind mission sitting in the Sun-Earth L1 Lagrange point; and Europe’s Solar Orbiter mission, which is also gets up close and with the Sun, but in a higher inclination orbit.
Analysis of the data supplied by these observatories reveal that the burst came from a large magnetic structure in the Sun’s outer atmosphere called a helmet (or coronal) streamer. These are distinctive V-shaped loops of matter rising away from regions on the Sun’s surface which have the opposite magnetic polarity to the surrounding areas and the corona. They can rise up to 1.5 solar radii before lopping back to the surface, with the solar wind often pushing the uppermost material even further from the Sun in the form of tapering spears or stalks. These spears can occur at any time in the Sun’s 11-year cycle, but during periods of solar minimum then tend to form around the heliographic equator and are far less prominent.
However, during periods of solar maximum, they tend to be more symmetrically distributed around the Sun, and like the Type IV radio bursts, can be portents of a CME, as the latter can often start at the base of such a streamer, with the “cavity” in the streamer’s loop becoming the conduit through which the core of the CME then rises and is ejected from the Sun.
In the case of the August 2025 radio burst, the data gathered by the four probes revealed that no fewer than three CMEs had originated in rapid succession from the base of the one streamer – which in itself is unusual. Lead to also three CMEs becoming one massively supercharged event which fortunately did not intercept Earth in its orbit, but which did feed a huge amount of energy into the radio burst, leading to its longevity.
What is not understood is why these three CMEs occurred in pretty much overlapping proximity. Where they a freak occurrence, or a further sign the Sun is experiencing changes in its behaviour? If the latter, then is it something that is related to the squeezing of the layer in which the majority of the Sun’s magnetic activity occurs, or something else entirely? Will it become more expected during periods of solar maximum, and if so, what does it mean for our space-based systems?
Right now, the answers are far from clear – but the findings of both BiSON and the recording of this massive radio burst and recognition of its underlying cause reveal that the more we learn about our Sun, he more we have yet to understand about its complex nature.
Zevzda Leak: NASA and Roscosmos Again at Odds
I’ve written about the long-standing atmosphere leak aboard the International Space Station (ISS) on several occasions – the last being in 2024. An issue for some seven years now, the leak lies within the aft airlock of the Russian Zvezda (aka PrK) module. Several attempts have been made to fix the issue down the years and none have succeeded.
At the time I last wrote about the situation, NASA and Roscosmos had once again figuratively butted heads on the issue and its possible cause. In 2024, the Russian space agency was adamant the slow leaks were the result of thermal contraction and expansion as the ISS orbited the Earth, passing in and out of sunlight and thus experiencing large swings in temperature across its structure.
NASA, however, was of the opinion that the leaks are indicative that the airlock itself was at risk of failure, the result of the massive stresses periodically placed on it.
To explain: the airlock at the aft end of the Zvezda module is aligned to the station’s centreline, making it one of the main ports used to carry out periodic and necessary “reboosts” to raise the station’s orbit as the tenuous drag of Earth’s upper atmosphere causes it to slowly descend. Whilst there are other ports on the station which can perform such reboosts, it is the Zvezda port which has commonly been used for boosting operations as Russian Progress resupply vehicles are well suited to the task. NASA has therefore been – and remains – of the opinion that these operations over the years have placed enormous stress on the airlock structure, resulting in the micro-cracks and the atmosphere leaks.
Because of this, NASA and the European Space Agency have long called for use of the Zvezda module to be discontinued, and the hatch linking it to the rest of the ISS permanently closed. Russia has disagreed, mainly because the docking element in question houses the connectors required to bring propellants for the station’s stations manoeuvring thrusters located in the Russian section of the station and the delivery of water supplies for the crew. Thus, losing the use of the docking port limits the station’s ability to carry out the kind of minor orbital adjustments it needs to avoid space debris, etc., and also potentially limits crew activities within the Russian section of the station.
As a compromise, it was agreed that as there was not an imminent risk of explosive decompression (or anything remotely violent), the hatch linking Zvezda should remain closed unless the module was in use – and that use would be largely limited to off-loading Progress craft. And there the matter has largely rested – until the late April 2026.
That was when Progress MS-34 docked with Zvezda with supplies for the station. Almost immediately after the vehicle’s arrival, the atmosphere loss within the module increased; not enough to endanger the station, but enough to be noticed. After monitoring the situation for a month, Roscosmos decided to take action – by ordering the cosmonauts on the station to drill into the module’s structure and then cut away part of a structural support.
This didn’t exactly go down well at NASA and ESA. Objections were lodged, exchanges became heated – and Roscosmos stop responding to the other agencies, declaring the operation would go ahead on June 5th. In response, NASA and ESA declared an emergency and ordered the three US and one French astronaut into the docked Crew Dragon under shelter in place / safe heaven rules, meaning they should be ready for immediate departure should anything happen.
This caused Roscosmos to reconsider their idea and ultimately call it off. Several further days of discussions were held and a compromise was eventually reached. This will see Zvezda sealed and depressurised so it is no longer directly used. However, Progress resupply missions carrying propellants and / or water will dock with the module for the purpose of transferring these items (which can be done automatically). Otherwise, Progress dockings (including those bringing propellants / water to the station alongside of other supplies) will occur at other docking ports in the Russian section of the station to facilitate the transfer of supplies.
Inara Pey: Living in a Modemworld 