Big changes are about to occur on the Sun. Anything that happens on the Sun is big of course—especially to the pipsqueak planets that orbit it and, at least in the case of Earth, depend on it for life. But this time the changes are big even by solar standards: The Sun’s magnetic field is about to flip upside down, its opposing magnetic poles switching places—north to south, top to bottom. It’s as though you took a bar magnet and rotated it 180°, except it’s the magnetism that rotates, not the magnet—and the magnet in this case is a million miles (1.6 million km) across, has a surface temperature of about 11,000°F (6,000°F) and weighs about 2,000,000,000,000,000,000,000,000,000 tons, give or take. So definitely big.
It’s hard to say exactly when the reversal will happen, but it’s been slowly unfolding since the summer. Scientists won’t know for certain if the flip is complete until December 7, when the south solar pole, which we currently can’t see due to the inclination of the Sun, comes into view. When that happens, astronomers will be ready with some of the best solar telescopes they’ve got: the powerful Wilcox Observatory, operated by Stanford University; the McMath-Pierce Solar Telescope in Arizona; and the space-based Solar Dynamics Observatory and Solar & Heliospheric Observatory (SOHO). And what they learn about the still-mysterious inner workings of the Sun could have implications for global communications, satellite operations and even the health and safety of human beings in space.
The solar flip-flop coincides with the event known as “solar maximum,” a time when sunspot activity is especially intense, leading to huge solar flares and coronal mass ejections, which send bursts of particles screaming out into space. That upheaval, known quite appropriately as “space weather,” can trigger intense auroral displays (aka the Northern and Southern lights), and even disrupt satellite communications. The worst solar storm on record, called the Carrington Event, after Richard Carrington, the British astronomer who observed it, happened in 1859. While there weren’t any satellites to disrupt back then, the electromagnetic blast that reached Earth caused telegraph wires to heat up and burst into flames.
But it’s not at all unusual for storms like this to break out and for the Sun’s magnetic field to flip. Both the solar maximum and the magnetic reversal happen every 11 years, in fact, in a cycle that has been going on for millions or even billions of years. “Astronomers first documented the existence of sunspots in the early 1600’s,” says Todd Hoeksema, a solar astronomer and director of the Wilcox Observatory, and scientists realized there were sometimes more of these dark blotches and sometimes fewer.
It wasn’t until the mid-1800’s, though, that they realized the blotches spread like an outbreak of solar poison ivy, then receded, then spread again in a regular rhythm—and looking back at earlier records realized that the rhythm could be traced at least back to about 1700. “We’re now at the maximum of Cycle 24,” Hoeksema says, and about to go into Cycle 25.”
The magnetic flip doesn’t cause the sunspot activity, though: it’s actually the reverse. Sunspots are places where magnetic field lines emerge from beneath the solar surface. They’re blazingly hot, but sufficiently cooler than the surrounding areas that they seem dark by contrast. And when they get big enough and numerous enough, they force the Sun’s overall magnetism to change direction. Things calm down after that until, about five years later, sunspots begin to increase again as our parent star winds up toward the next maximum.
It all sounds pretty routine, really, but there’s one caveat: sometimes, for reasons solar experts still don’t understand, sunspot activity dwindles and stays that way for a while. From the mid-1600’s until about 1715, observers saw barely any sunspots, even during the most intense part of the solar cycle. “They may have still been there,” says Hoeksema, “but been too weak for anyone to notice them.”
During this period, known as the Maunder Minimum, temperatures in Europe were abnormally low—so low that people could (and did) ice skate on the Thames, which never freezes today. The relationship between sunspots and temperature may not have been a coincidence. “When the Sun is less active,” says Hoeksema, “it’s also less bright, and puts out less energy.”
The Maunder Minimum may not be a one-off event. Cycle 24, just ending, was about half as active as usual for the past century, and Cycle 25 is tentatively looking as though it might be weak as well. This has led to speculation that we might be entering another decades-long sunspot low, which could temporarily mitigate the effects of global warming.
Unfortunately, that’s a long shot. The Maunder Minimum came at the end of a much longer period known as the Little Ice Age, so solar cooling was clearly not the only cause. The Sun does cool during sunspot-free periods, but only, says Hoeksema, “by a few tenths of a percent.”
A loss of sunspots would have more significance for space weather: with fewer solar storms, Earth would be relatively free of the electronic communications glitches that can result. Moreover, astronauts en route to destinations like Mars would have fewer occasions to huddle in radiation shelters while a space storm raged outside.
But there’s a downside too. When the Sun is quiet, the heliopause—the boundary region where the solar wind slams into the particles of interstellar space—relaxes as well. That allows high-energy cosmic ray particles, normally kept at bay, to penetrate deep into the Solar System. So while the radiation from solar storms would be reduced, the radiation from outside would increase. “If I were going to Mars,” says Hoeksema, “I’d go at solar max, because solar events are somewhat predictable, and they don’t last very long.”
As a scientist, meanwhile, Hoeksema loves the idea that the Sun might be entering a new, low-activity phase. “We don’t really understand why some cycles are stronger than others,” he says, “and there’s nothing scientists like better than a mystery.” The sun, which has never lacked for those, may be about to offer up a few more.
(INTERACTIVE FEATURE: Interactive “Comet of the Century” Tracker. Where’s ISON Now?)