Do you remember what you were doing on July 23, 2012? Earth dodged quite a bullet that day... a huge magnetic bullet. Two solar eruptions collided into a superstorm, sending a pulse of magnetized plasma barreling through Earth’s orbit.
Lucky for us, Earth and the other planets were on the other side of the sun. But if the eruptions had happened just nine days earlier -- when the ignition spot was aimed at Earth -- it would have hit the planet, potentially short-circuiting power grids, disabling satellites and GPS, and just generally wreaking havoc on our electronic lives.
Coronal mass ejections (CMEs) are large-scale eruptions of plasma and magnetic field from the outer layer of the sun. As the most intense eruptions on the solar surface, they typically release energies equivalent to that of about a billion hydrogen bombs. While they're a huge influence on space weather, by the time they reach us, the effects of most CMEs are about the same as normal solar winds -- that is, with the speeds and magnetic field strengths comparable to the streams of charged particles from the sun we experience every day.
To better understand how they change as they travel from the sun, a team led by Ying Liu of the Chinese Academy of Sciences’ National Space Science Center used multi-point sensing satellites to study the rare case of two consecutive eruptions that occurred on July 22-23, 2012. The magnetic storm was detected by NASA’s STEREO A probe, which circles the sun ahead of us in Earth’s orbit (its twin, STEREO B, trails in our orbit).
Based on their analysis of the 2012 event, the team concluded that the rapid succession of two CMEs resulted in an extreme space weather storm -- a "perfect storm" -- with a remarkably high solar wind speed and magnetic field. Specifically, the interactions of the two nearly simultaneous CMEs -- separated by only 10 to 15 minutes -- enhanced them into a superstorm with 5 times the normal speed and 10 times the magnetic field strength of a typical CME at Earth's orbit.
The huge outburst propelled a magnetic cloud through the solar wind at a peak speed of more than 2,000 kilometers per second. The speed was so high because another mass ejection four days earlier had cleared the path of material that would have slowed it down, weakening the solar wind and the magnetic field for the subsequent two CMEs to travel through.
In this video, you can see the solar superstorm arising from two successive, interacting eruptions. The white dots are the “snowstorms,” produced by energetic particles impacting the cameras. The shock wave of charged particles washed over the probe’s sensors in just 18.6 hours.
Aside from the speed of the one-two punch, the event was dangerous because it produced a southward-oriented magnetic field, which, had it hit us, would have merged violently with Earth’s northward field -- driving large magnetic storms and creating auroras all the way down to the tropics. “These gnarly, twisty ropes of magnetic field from coronal mass ejections come blasting from the sun through the ambient solar system, piling up material in front of them, and when this double whammy hits Earth, it skews the Earth’s magnetic field to odd directions, dumping energy all around the planet,” study coauthor Janet Luhmann of UC Berkeley explains in a press release.
The largest magnetic storm ever reported on Earth was the Carrington Event of 1859; the telegraph system was knocked out across the U.S. and northern lights (aurora borealis) lit up the night sky as far south as Hawaii. “But the effect today, with our modern technologies, would have been tremendous,” Luhmann adds. A small event in 1989 resulted in electricity loss to six million people for up to 9 hours. The cost of a solar storm like the Carrington Event could reach $2.6 trillion worldwide and could take 4 to 10 years to recover.
The findings were published in Nature Communications this week.
[UC Berkeley release, NASA release via Nature, Science]
Video: Ying Liu