There’s something special about the sun: It’s a bit boring

The sun, like all stars, is a blazing ball of fusion-powered plasma. From its surface emerge magnetic field lines that can cause dark patches known as sunspots. Turn up the activity of these magnetic whorls, and you get more solar storms flinging deadly charged particles and radiation throughout our solar system. If enough of these punishing waves hit a rocky planet, that planet might end up microwaved into a dreary condition where nothing could live.

So how is it that we’re alive? A study in the journal Science suggests that our sun is rather tame compared with its stellar siblings, and that hundreds of other sun-like stars in our galaxy have on average five times more magnetic activity than our parent star. In other words, the sun is a bit humdrum, which might be good for life on Earth.

Astronomers have been tracking the appearance of sunspots since the time of Galileo, providing a proxy for solar activity stretching back four centuries. Some previous studies also implied that the sun was quieter than other similar stars. But competing evidence has also found the sun’s activity level is normal for stars of its size.

“This triggered the question: ‘Is the sun a real sun-like star?’” said Timo Reinhold, an astrophysicist at the Max Planck Institute for Solar System Research in Göttingen, Germany, and co-author of the paper.

Reinhold and colleagues looked at data collected by NASA’s retired Kepler space telescope, which continuously monitored approximately 150,000 stars in the Milky Way for four years to find exoplanets, and was capable of observing brightness variations from activity such as the appearance and disappearance of starspots.

The researchers selected stars with masses, temperatures, ages, chemical compositions and rotation periods comparable to our sun’s. They eventually found 369 stars for comparison, the largest such sample to date.

Stars like the sun go through regular cycles during which spots cross their surfaces with greater or less frequency. During times of peak magnetic activity, when spots pop out all over the surface, a star will dim. Our sun’s cycle lasts about 11 Earth years.

For the sun, this dimming is negligible.

Data from the past 140 years indicates that its brightness changes by less than a tenth of a percent over the course of its cycle. But for the stars studied by Kepler, the variability could be up to 12 times that amount.

The 369 sun-like stars observed by Kepler might simply be in an earlier stage of evolution than the sun, these scientists say. Or perhaps something particular about the sun is causing an early transition. Reinhold’s team doesn’t favor one explanation over the other.

In either case, a quiet sun has benefited our species. When the sun flares up, its energetic emissions do harm to astronauts and satellites in orbit, and especially powerful outbursts can affect power grids down on the ground.