Slowdown By Sun Puzzles Astronomers

A puzzling slowdown by the Sun is leading some to wonder whether the world might be heading for a new mini ice age. Three separate studies reveal that a regular cycle of activity inside our home star may be rapidly dying. 

The Sun imaged from the SoHo space observatory (NASA)

When something similar happened three centuries ago, it coincided with a prolonged cold spell on Earth, though scientists are quick to point out that this may indeed just have been a coincidence.

Nuclear reactions inside the solar furnace, driven by magnetic forces, usually produce a regular ebb and flow of features like dark sunspots. Generally this cycle peaks every 11 years or so, when the Sun’s visible surface ends up covered with a dose of cosmic acne.

The last solar minimum was surprisingly prolonged with no spots at all on the Sun for many months on end. By now the Sun would normally be showing a good number of spots as so-called Cycle 24 build-up to the next maximum, but it is still relatively quiet, despite occasional violent storms and coronal mass ejections that spark auroral displays on Earth.

Now astronomers are warning that the next scheduled cycle of solar activity, Cycle 25, might not happen at all. Three independent studies presented at a meeting of the Solar Physics Division of the American Astronomical Society in New Mexico delivered a similar message – the Sun is heading for a quiet spell.

The last time the Sun “died” like this was in the late 1600s and early 1700s, an event termed the Maunder Minimum.  At the same time there was a period of severe cooling on Earth which became known as the Little Ice Age. As temperatures plummeted, rivers and canals froze over.

Farms and villages were destroyed by spreading glaciers in Switzerland and people were able to cross the frozen Baltic from Poland to Sweden on foot.

The first clue that something is amiss in the Sun, discovered by Frank Hill of America’s National Solar Observatory, is the absence of a jet stream current that should by now have started up to begin the next cycle of activity after the present weak one.

A second sign, reported by Richard Altrock of Sacramento Peak Observatory, lies in the Sun’s tenuous atmosphere, the corona. The usual flow of magnetic activity towards the poles that should be happening at this stage has failed to occur. This is thought to point to changes deep within the Sun.

Thirdly, the strength of the magnetic field inside sunspots observed in recent years has been much weaker than expected and in a steady decline, according to data collected by Matt Penn and William Livingston at Kitt Peak Observatory, Arizona. If it continues, the Sun will have lost its spots completely by 2022.

Dr Hill said of the Sun’s behaviour: “This is highly unusual and unexpected. But the fact that three completely different views of the Sun point in the same direction is a powerful indicator that the sunspot cycle may be going into hibernation.”

Scientists do not know enough about how the Sun affects our weather to tell whether its apparent slowdown will also slow the effects of global warming.

UK solar expert Dr Lucie Green, of the Mullard Space Science Laboratory in Surrey, told Skymania: “Overall the Sun is getting quieter, but I do not think we can conclude a new Maunder Minimum is on it’s way!”

It all makes a change from worrying about whether an over-active Sun might wreak devastation on our hi-tech planet.

Reporter: Paul Sutherland