After Two Decades of Calm, the Sun’s Unforeseen Activity Alarms NASA

The Astrophysical Journal Letters. It is based on data from several space probes, including Ace and Wind, active since the late 1990s.

An unexpected reversal

For almost three decades, the signals emitted by the sun seemed to converge on the same conclusion: our star ended up towards a long phase of calm, comparable to that observed between 1645 and 1715, known as the name of Minimum of Maunder. This hypothesis was based on concordant indicators, including a gradual decrease in the number of solar spots and a weakening of the solar wind. In 2008, this trend reached a historic low point. The set of parameters measured – thermal pressure, plasma density, intensity of the magnetic field – showed values ​​never recorded since the start of modern surveillance.

But since that date, the measures transmitted by the ACE probes (Advanced Composition Explorer) and Wind, exploited by NASA, reveal a progressive tilting. Jamie Jasinski, researcher at the Jet Propulsion Laboratory, coordinated an in -depth analysis of this data. He confirms that all the indicators have started upwards. The solar wind increased by 6 % speed, its density of 26 % and its temperature by 29 %. The intensity of the interplanetary magnetic field increased by 31 %.

This unexpected evolution questions the scenario of a modern “big minimum”. “” The sun is coming out of a decline cycle of almost 20 years “Said Jasinski in a press release. This progressive awakening is already accompanied by an increase in visible manifestations of solar activity, such as stains, eruptions or coronal mass ejections. The announced calm seems to have given way to a dynamic of sustainable recovery.

Solar cycles with complexity still misunderstood

The behavior of the sun is structured in cycles of about 11 years, called Schwabe cycles. During these phases the number of sunscreens increased and then decreases. These cycles are themselves registered in longer variations, such as the Hale cycle22 years old. The latter is linked to the inversions of the solar magnetic field. However, if the short cycles are relatively well modeled, the longer -lasting fluctuations still largely escape the understanding of astrophysicists.

Since the first systematic observations in the 17th century, astronomers have spotted several phases of prolonged calm. In addition to the minimum of Maunder, the Minimum Daltonbetween 1790 and 1830, also marked a clear decline in solar magnetic activity. However, according to Jasinski, current models do not explain why such long cycles appear or disappear. “” Long -term trends are much more difficult to predict. We do not yet know why the sun has experienced a period of low activity so prolonged at the end of the 18th century He admits.

Some researchers advance the hypothesis of a Gleissberg cycleof the order of 100 years. It would modulate the amplitude of 11 years cycles. But this Centennial cycle remains poorly characterized, and recent data do not yet confirm this modulation. The recent increase in solar activity could thus mark the end of an atypical phase, without however indicating a return to a well -defined standard.

Solar science therefore remains confronted with a deficit of structural explanations over long periods of activity or inactivity, despite decades of accumulated data. This uncertainty makes the forecast of extreme events more difficult to establish. It limits the ability to anticipate potential impacts on technological systems.

An intensity of unexpected activity from the current cycle

The solar cycle 25, started in December 2019, was, according to the initial forecasts, be comparable or slightly lower than the previous one, deemed particularly low. The Space Weather prediction Center (SWPC), bringing together NOAA and NASA, anticipated moderate solar maximum around 2025. This forecast was based on traditional models, which extrapolated the slow decay started since the 1980s.

But as early as 2023, observations contradicted these estimates, reports LiveScience. The number of solar spots exploded much earlier than expected, reaching levels in 2024 never seen for over 20 years. This discrepancy forced the SWPC to publish an unprecedented update of its forecasts. In parallel, the number of class X solar eruptions, the most energetic, has also experienced a significant increase. These phenomena, detected by observation instruments such as those of Solar Dynamics Observatory (SDO), testify to a revival of the magnetic activity of the sun.

This strengthening appeared spectacularly in May 2024, during a geomagnetic storm classified “extreme”. This storm, caused by a particularly powerful coronal mass ejection, caused boreal aurora to the average latitudes, but also disturbances on electrical networks and satellites. Economic damage has been estimated at more than $ 500 million.

The current cycle, which has not yet reached its official maximum, could therefore be much more active than anticipated. The direct consequences on land and orbital infrastructure are no longer only hypothetical. This sun awakening could become the new standard for future cycles.

Technological vulnerability in the face of the vagaries of the sun

Certainly the revival of solar activity remains fascinating for scientists. However, it represents a concrete risk for modern companies strongly dependent on space and digital technologies. The sun, through its storms and eruptions, can disrupt electrical systems, damage satellites, cause GPS positioning errors, or even compromise the safety of inhabited spatial missions.

Energy particles from solar eruptions and coronal mass ejections (CME) can reach the earth in a few tens of hours. When they interact with the terrestrial magnetosphere, they trigger geomagnetic storms. The latter induce electric currents in high voltage lines. In 1989, a storm of this type had caused a total breakdown of the electricity network in Quebec. However, modern structures, more interconnected and more sensitive, are even more exposed today.

Satellites are also vulnerable. High energy particles can damage their electronic components, alter their orbits by draft effect in the heated atmosphere, or even cause contact losses. In February 2022, a geomagnetic storm had caused the loss of 40 Starlink satellites shortly after their launch.

Faced with this growing threat, NASA, in collaboration with the NOAA, prepares several missions dedicated to the forecast of the space climate. Among them, IMAP (Interstellar Mapping and Acceleration Probe) and SWFO-L1, a satellite on the watch of the solar storms positioned at the point of Lagrange L1. They will obtain data in real time to better anticipate the impacts.

The sun's awakening therefore requires an urgent adaptation of the strategies for the protection of critical infrastructure. The precise monitoring of its activity becomes an essential condition to guarantee the resilience of the systems that structure our connected companies.