The space storm, perhaps the third most powerful on record while in space, packed the potential to have more effect than one in 1989 that knocked out power to an entire Canadian province.
"This is one of the largest space weather events I've seen in 30 years," Joe Kunches, lead forecaster for NOAA's Space Environment Center, said in a telephone interview.
The brunt of the storm, a coronal mass ejection (CME), hit at around 1 a.m. EST Wednesday, reaching Earth about 19 hours after it left the Sun -- several hours sooner than expected.
"This makes it one of the fastest CME's we have recorded and comes close to a record superstorm in 1859," said Paal Brekke, deputy project scientist for the SOHO spacecraft, which first spotted the event.
Forecasters had feared the cloud of charged particles might fuel one of the worst geomagnetic storms in recorded history. The outcome depended on the whether the storm's magnetic orientation was the same or different than that of Earth's magnetic field. For the most part, it appears the alignment did not favor the worst outcome.
As of 11:30 a.m. EST the storm was still buffeting Earth's environment but the strength had waned slightly.
A giant magnet
Earth can be thought of as a giant magnet. Invisible magnetic field lines emanate from the planet's poles and extend out into space, beyond the atmosphere, to create a giant sphere of protection against solar particles. The Sun emits a constant stream of these particles, a so-called solar wind. Storms vastly enhance the output.
"The magnetic cloud slammed into the Earth's magnetosphere and created a G5 geomagnetic storm, the strongest category," Brekke explained. "However, the storm seems to weaken already and this is probably caused by the fact that the CME had a northward pointing magnetic component."
Brekke said the setup may have prevented a much more severe and long-lasting geomagnetic storm.
"We were quite lucky I would say," Brekke said.
Kunches noted that the magnetic direction of the storm could change before it is over, causing a burst of problems.
In addition to threatening satellites in space and power grids on Earth, the storm was expected to generate colorful Northern Lights well into mid-latitudes of the United States and Europe today into early Thursday.
The NASA-run web site Spaceweather.com reported today that aurora had been spotted as far south as central California, New Mexico, Texas, and Oklahoma, signaling the storm's swift arrival and strong potential.
Residents of high latitudes, such as Alaska, may enjoy enhanced aurora activity for several more hours. It is not clear if tonight will bring more aurora for mid-latitude skywatchers, though early forecasts have suggested that would be the case. Experts say it can take a day or more for a big storm to blow completely past the planet.
Auroras, also called the Southern and Northern Lights, are created when the charged solar particles stream down Earth's magnetic field lines and excite oxygen and nitrogen atoms in the atmosphere, near the poles. Normally the auroras are only visible from places near the poles, like Alaska. But when Earth's magnetic field is overwhelmed, the aurora can dip will into the United States and Europe.
"If this continues, there might be good aurora tonight," Brekke said in a telephone interview just before Noon EST. "But its hard to tell how long this cloud is and how dense it is."
A severe space storm can effect any sort of surface transmission lines -- from power to phone and even pipelines -- as extra current is induced, potentially overloading wires or switches.
Satellite operators and power grid managers had prepared to endure a potentially damaging event when forecasters on Tuesday announced the storm's impending arrival. It is not yet clear if any other damage has been done. Commercial satellite operators are loathe to admit problems, however, and are not required to do so.
The Japan Aerospace Exploration Agency (JAXA) also said it had lost contact with its Advanced Earth Observing Satellite II, Midori-II, on Oct. 25. The reason is not known. A series of solar storms began late last week, but there has been no connection made between any of the storms and the Midori-II.
Astronauts aboard the International Space Station took cover from heavier radiation sent out by the flare. They were not expected to be in any serious danger, but they retreated to the Zvezda service module -- the most heavily protected -- several times Tuesday and again Wednesday.
Engineers can put some satellites into hibernation modes and reduce the operations of others to reduce the risk of electrical disruption or destruction. The storm, however, can also swell Earth's upper atmosphere, creating drag that can pull a satellite out of orbit.
Power grid operators arrange for less switching and fewer large-scale power swaps.
While apparently not a catastrophic event at Earth, the storm as it left the Sun remains historically interesting.
Kicked up at about 6 a.m. EST (1100 UT) Tuesday, the major solar outburst came on the heels of four other flares late last week and over the weekend. All were considered fairly severe, but the latest eruption makes the others seem like solar sneezes.
Tuesday's blast was classified as an X17, where X denotes a major flare and larger numbers are stronger. That compares to two flare-ups over the weekend that were rated less than X2.
"The flare may be the third strongest X-flare on record," Brekke said.
A slightly stronger flare on April 2, 2001 was not pointed at Earth. This week's storm was headed directly at us.
The space storm is intrinsically stronger than one on March 6, 1989 that tripped a power grid in Quebec, Canada.
Lesser storms have caused satellite problems. In 1997, an AT&T Telestar 401 satellite used to broadcast television shows from networks to local affiliates was knocked out during a solar storm. In May 1998 a solar blast disabled PanAmSat's Galaxy IV. Among the casualties: automated teller machines; gas station credit card handling services; 80 percent of all pagers in the United States; news wire service feeds; CNN's airport network; and some airline weather tracking services.
The greatest solar storm on record occurred in 1859, shorting out telegraph wires and starting fires in the United States and Europe. Brekke told SPACE.com that if this week's storm had hooked up with Earth in just the right way, it could have been about one-third as strong as the 1859 tempest and possibly stronger than the 1989 event.
The coronal mass ejection is one in a series sent out by two huge sunspots, the largest pair to grace the Sun at one time in recent memory. Sunspot 486 was responsible for this blast.
More major flares and space storm are possible in coming days, forecasters said.