Staring at the Sun
On the morning that NASA’s MESSENGER spacecraft was scheduled to pull into orbit around Mercury after its near seven year journey, Michael Hesse, chief of the Space Weather Laboratory at NASA’s Goddard Space Flight Center, noticed something on his monitor: A bright flash of ionized gas spewing from the sun.
“It looks like we have a CME,” Hesse said. Images on a computer screen captured by NASA’s twin STEREO spacecraft showed a burst of light. He clicked on the screen. ”Here you see it now. It’s going away from the Earth, but it may still go to a place NASA cares about,” he said. ”Like Mercury.”
CME is short for Coronal Mass Ejection. These are balls of gas ejected from the sun’s outer atmosphere, consisting of charged particles and magnetic field. The eruptions occur when magnetic energy in the sun piles up and then gets suddenly released in a twisting motion caused by convection in the sun’s outer zone. The fastest CMEs travel as fast as 93 million miles in a day. That’s millions of miles per hour.
Within minutes, a team of heliophysicists had gathered in an operations room at Goddard’s Space Weather Laboratory. “It could be that there are two different ones,” said scientist Aleksandre Taktakishvili, studying the images.
Huddled around the monitors, they noted the direction of the solar burst – it was moving away from the Earth. Using images from different spacecraft, they studied it from various angles, and determined its size, shape and velocity. Then they stuck those parameters into a model.
The model they use, called WSA-ENLIL, is a nod to Enlil, a Sumerian lord of wind and storms. Enlil, who wears a crown of horns, is known for being a kind but also cruel god who sends forth disasters, including a great flood that wiped out humanity.
When launched, the ENLIL model generates an animated spiral with the sun in the middle, the planets surrounding the sun in orbit and the coronal mass ejection propogating outward, revealing its direction in relation to the planets.
Scientists at the Space Weather Laboratory monitor data captured from various space satellites and beamed back to earth. Screens in their operations room show the various measurements. The Solar Dynamics Observatory (SDO) spacecraft measures ultraviolet bursts. The twin STEREO probes and the Solar and Heliospheric Observatory (SOHO) probes capture visible images, similar to photographs of solar weather.
“A solar eruption can have any of following features,” Hesse said. “It can have an X-ray burst, a UV burst, there can be visible light and there can be energetic particle acceleration. Sometimes they happen altogether. Sometimes only some of them happen.”
A solar flare that erupted on Valentine’s Day and sent charged particles and radiation coursing toward Earth grabbed headlines for being the most powerful flare in four years, but had little obvious impact, other than disrupting some radio communications in China and creating a spectacular set of northern lights, or aurora borealis.
But they’re not all harmless. When powerful solar eruptions go earthbound, these electrical storms can disturb the Earth’s magnetic field, jolting and disrupting satellites and power grids. The upper atmosphere of the earth, the ionosphere, becomes turbulent, like an ocean in a storm. And our Global Positioning System, which lives within satellites above the ionosphere, has to punch through that electrical storm to send its signals to earth.
“The signals might become unavailable to you,” said Joseph Kunches, a space scientist from NOAA’s Space Weather Prediction Center. “You might have errors embedded in the system. That’s where the rubber meets the road. There’s not much you can do. The power is set when it’s up in the satellite, and you can’t turn the volume up.”
A geomagnetic storm in 1989, for example, knocked out the power grid in Quebec, disrupting power through most of the city.
On this particular day, MESSENGER spacecraft operators were alerted to the slightest possibility of a glancing blow to Mercury, but the planet and space probe made it through unscathed.
Like Earth, the sun has a seasonal cycle: a quiet phase that lasts roughly two years, followed by a stormy season. The time varies. This last solar minimum was unusually long.
But the sun has now awakened from its hibernation phase, and is climbing toward the most turbulent part of its cycle, the so-called solar maximum, when solar eruptions become stronger and more frequent. That solar maximum is expected to peak in 2013.
Threats from solar eruptions have become increasingly risky as we’ve become more dependent on weather and navigation satellites. “We have way more technology that’s susceptible to these effects and we rely on it much more,” Hesse said.
At their most powerful, solar storms can disrupt GPS signals and blow out transformers. Air travel will become more vulnerable, as the Federal Aviation Administration transitions to the Next Gen system, which will allow for more traffic in the airways, but be much more reliant on GPS.
Much of this can be avoided, Hesse says, by good forecasting, advanced alerts, and reducing the electrical load on transformers to prevent geomagnetically induced current from overloading them.
“But this is if nothing surprising happens,” Hesse adds. “With a huge X-ray burst, GPS could be reduced over the entire dayside of the earth. And that can happen out of the blue. You can’t do much to prevent that from happening.”
Understanding the genesis of these flares – why they happen – is central to the research, and one of the field’s still unanswered questions, he added: “If I could tell you that at 10 a.m. EST, there would be a big eruption, we’d be so far ahead of the game. It would let us act preemptively.”