The first of an unprecedented series of powerful solar storms that punished Earth late in 2003 is now at the edge of the solar system, some 8 billion miles (13 billion kilometers) away, poised to move beyond the farthest manmade object in the cosmos.
Scientists have monitored all the storms' progress with a fleet of spacecraft arrayed between Earth and the near the edge of the solar system. Each event flung billions of tons of matter into space in clouds that expanded, slowed down and were diluted.
But the storms remained strong while clear out at the giant planets and beyond. One disrupted the magnetic fields of both Jupiter and Saturn, creating fresh localized storms similar to those that strike Earth in the hours after initial eruptions.
"It's striking that this blast wave was powerful enough to generate a magnetic storm all the way out to Saturn, almost ten times farther from the Sun than Earth is," said Ed Stone, a physics professor at Caltech.
Another storm stole air from Mars, hinting at where water that was once abundant on the red planet might have gone.
The findings were presented to reporters during a NASA teleconference Thursday.
During late October and early November of 2003, 10 powerful solar flares kicked up extreme doses of X-rays and other radiation, along with slower-moving storms of charged particles. One flare was by far the most powerful ever measured.
All the eruptions were spawned by huge, magnetically unstable sunspots during a two-week stretch of heightened solar activity unlike anything on record. Expanding clouds of charged particles known as coronal mass ejections (CMEs) raced into space.
The events were spotted in their infancy by the SOHO spacecraft, which sits partway between Earth and the Sun.
A few of the CMEs moved abnormally quickly, reaching Earth in less than a day and helping scientists to later determine a speed limit for the electrified gas clouds. One set a new space speed record of 5 million mph (2,235 kilometers per second).
"It's the largest speed we've ever measured in space of a gas stream from the Sun," said Thomas Zurbuchen of the University of Michigan in Ann Arbor.
The storm later slowed down. Its average speed has now been put at about 1.5 million mph (670 kilometers per second).
Some of the light-speed radiation and particle-based CMEs slammed squarely into our planet, hampering radio communications, forcing the FAA to divert airline traffic away from polar routes (which are exposed to higher radiation doses), and crippling two Japanese satellites. Astronauts aboard the International Space Station took cover multiple times in protected areas.
More than half of all NASA spacecraft showed anomalies during the storm, Zurbuchen said. People as far south as Virginia were treated to fantastic auroral displays in the night sky.
Smacking into Mars
Initial radiation from the solar flares — radio waves, visible light and X-rays — traveled at light-speed, well ahead of the clouds of charged particles. The Cassini spacecraft, then past Jupiter en route to Saturn, recorded the sound of one storm swooshing by less than two hours after the eruption.
The not-quite-so-swift gas clouds raced on to the orbit of Mars and beyond. One of these radiation tempests exercised a little cosmic irony by knocking out a radiation-monitoring instrument on NASA's Mars Odyssey orbiter.
Odyssey was, however, able to record how the blast compressed and stretched the atmosphere of Mars, which is only about 1 percent as dense as Earth's atmosphere. Mars has no globally protective magnetic field like Earth, so the storm interacted much differently there than it does here.
"Substantial parts of the upper atmosphere [of Mars] escaped into space," Zurbuchen said.
Zurbuchen said similar solar events over the course of 3.5 billion years might have contributed to the loss of Mars' atmosphere and water, a mystery researchers have been working on for decades since pictures revealed that Mars likely had large amounts of flowing water in the distant past.
To the edge of the solar system
The ominous clouds caught up with other probes launched years and even decades ago, as nervous engineers monitored the storms' rapid progress to the outer planets and beyond.
In mid-May the quickest of the blasts caught up with NASA's Voyager 2 probe, launched in 1977 and now about 7 billion miles (11 billion kilometers) away and nearing the edge of the solar system.
Sometime this month, the leading eruption is expected to catch up with Voyager 1, which also launched in 1977 and is now piercing the edge of the solar system more than 8.4 billion miles (13.5 billion kilometers) from Earth. That's 90 times the distance between Earth and the Sun, covered by the space storm in less than 9 months. Voyager 1 is the most distant probe ever sent by humans.
Later this year the blast should reach the true edge of the solar system, some 3-4 billion miles (4.8-6.4 billion kilometers) beyond Voyager 1. There the storm will meet head-on with a wave of interstellar particles at what's called the heliopause. Radio disturbances caused by that interaction then might be picked up by the Voyager craft, giving scientists their first measurement of where the edge really is.
Stone said the interaction will also temporarily push the Sun's influential boundary another 400 million miles (644 million kilometers) into space. It should rebound within a year or two.
Researchers plan to keep a continued watch.
The top priority in monitoring space storms is to predict their arrival, in order to safeguard power systems on Earth and satellites in space. A storm in 1989 disabled a large power grid in Quebec, and last year's storms were blamed for a minor power failure in Sweden.
For the most part, the storms do not threaten humans, though airline passengers on polar routes can get extra doses of radiation that leak through cracks in Earth's otherwise protective magnetic field.
Knowing how the clouds of radiation travel through the solar system could one day allow life-or-death forecasts.
If humans travel back to the Moon or on to Mars, they would be at great risk from solar storms unless housed in highly protective habitats or spacecraft. High doses of radiation from a storm — say, during a spacewalk — could be lethal. Lower doses over time might damage the central nervous system.
"Space radiation can also cause cancer and cataracts in humans," said Carl Walz, an astronaut and program executive for NASA's Advanced Concepts, Project Prometheus.
When Mars is on the other side of the Sun, storms that leap from the side of the Sun not visible from Earth could, given the current lack of monitoring devices in space, surprise anyone residing there, other NASA officials have said. Increased space travel would have to be matched by more Sun-monitoring spacecraft throughout the solar system.
The angry Sun has provided a useful lesson.
"Like a storm on Earth, the storms [in space] vary depending on which way they're going," said Eric Christian of NASA's Solar Physics Division, adding that there's a strong need to learn more about how the storms develop as the propagate outward. "We're in the early days of space weather forecasting now."
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