Eight months after storms exploded from the sun's surface at 5 million mph, the spectacular blast wave is still traveling to the edge of the solar system, scientists said yesterday.
A fleet of spacecraft on a variety of missions gave scientists an unprecedented opportunity to study the "Halloween storms" and their effects. On Earth, aircraft were rerouted, astronauts took cover in the international space station to avoid the effects and the aurora borealis surged southward to the Mediterranean.
The wave triggered magnetic storms on Jupiter and Saturn and peeled away parts of Mars's upper atmosphere. Scientists suggested that such storms, spread over billions of years, could explain how Mars lost the seas that once may have covered its surface.
"We know [from the Mars rovers] that there was water on the Martian surface," University of Michigan physicist Thomas H. Zurbuchen said at a NASA-hosted telephone news conference. "Where did it go? There's a number of ideas, and one of them . . . is a kind of erosion" caused by solar storms.
Scientists still await data from Voyager I, outward bound from Pluto 9 billion miles away, and in position, possibly, to record the blast wave's encounter with the heliopause -- the boundary between the bubble of matter and energy dominated by the sun and the vastness of interstellar space.
"We don't know exactly where the boundary is," said California Institute of Technology physicist Edward C. Stone. "We think it's 3 or 4 billion miles beyond Voyager I." When the blast wave reaches the heliopause, the meeting may trigger low frequency radio signals that Voyager can record and relay to Earth, he said.
The Halloween storms began Oct. 22 when solar flares began exploding from sunspots, emitting enormous surges of energy and radiation as billions of tons of charged particles deluged the solar system.
On Oct. 28, a solar flare triggered two "coronal mass ejections" that headed for Earth at 5 million mph. Although the Earth's magnetic field and atmosphere deflected harmful effects on the planet's surface, the blast wave caused an immense magnetic surge at the poles, forcing aircraft on high-flying polar routes to alter flight plans.
On the space station, astronauts took cover in the shielded Russian service module to avoid the radiation that accompanied the storm.
The excess magnetism caused both polar auroras to creep deep into temperate latitudes.
"These were enormous explosions," said Eric R. Christian, chief of NASA's solar physics division, but they were topped by a Nov. 4 surge, the most intense solar flare ever recorded. "In a short time, all these explosions combined to form an amazing blast wave."
Christian said scientists did not know how the explosions affected Mercury and Venus, because no spacecraft were in the vicinity, but they were watched by Earth-orbiting satellites and they disabled a radiation recording instrument aboard NASA's Mars Odyssey, which is orbiting the planet.
Zurbuchen explained that Mars's lack of a generalized magnetic field made it vulnerable to the storm of zooming magnetic particles. "The higher in space, the more [Mars's] atmosphere is charged," Zurbuchen said. "When a magnetic field comes by, charged particles want to follow it."
Zurbuchen suggested that solar storms probably depleted what may once have been a more robust Martian atmosphere, and may have helped break Mars's surface water into hydrogen and oxygen so it, too, was peeled away.
The blast swooped by Mars but began to slow as it moved outward. The Ulysses spacecraft tracked the wave as it passed Jupiter, and Cassini-Huygens picked it up as it neared Saturn.
In April the blast wave passed Voyager II, 7 billion miles from Earth, and headed toward the outer edge of the "bubble" defined by the solar wind.
Stone said the wave should push the boundary out 400 million miles farther into the thin gas between stars before the "interstellar medium" shoves the heliopause back into place.