Solar flare today zaps spacecraft camera with protons
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April 21, 1998: The sun itself has just provided a not-so-subtle hint that this sunspot cycle will be stronger than usual.
Above are quarter-sections of images from two of the SOHO coronographs before (left in each pair) and after (right) the spacecraft was showered with protons from the flare that caused the coronal mass ejection seen rising from the surface. The C2 coronagraph (left; (1018x504-pixel image) covers an area from 2 to 6 times the Sun's radius. The C3 coronagraph (1017x530-pixel image) covers from 4 out to 30 radii. In each, the Sun's disk is the small white circle drawn inside the occulting disk. So faint is the corona that stars can also be seen in these images. The full-size images (1024 pixels square, are available; go to the SOHO LASCO C2 and C3 images.
On Monday morning (about noon, UT, April 20), the sun emitted a medium-size flare that included a blast of high-energy protons that zapped the cameras on the Solar and Heliospheric Observatory (SOHO) in a "halo" orbit just outside the Earth's protective magnetosphere. The protons (recorded at right) appear as tracks inside the cameras' charge-coupled devices, the electronic retinas that build the images.
"SOHO has experienced things like this before, but this is the first time I've seen so much garbage," said Edwin Reichmann, a solar physicist at NASA's Marshall Space Flight Center. "This is another indication of the kind of stuff that will cause detectors to give false signals."
Reichmann is a co-author, with Dr. Dave Hathaway and Robert Wilson, also of NASA/Marshall, of a paper predicting that solar cycle No. 23 will be larger than usual, but not a record.
Reichmann said the flare that was observed Monday evening was classified as an M 1.4 flare as seen by solar X-ray monitors aboard a Geostationary Operational Environmental Satellite GOES-8; click on the image at right for a 2-day graph of X-ray data. Flares are measured on four levels - B, C, M, X - each 10 times stronger than the last.
At the same time, the SOHO's LASCO telescope saw a coronal mass ejection, an eruption of hot, electrified gas from the sun into deep space.
"Most of the flares we have in a solar cycle are C-class," Reichmann explained. "As the cycle proceeds toward maximum, we begin to see M- and X-class events." The biggest flare on the last cycle was an X13, 100 times more powerful than what was seen Monday. (The scale runs X1 to X10, but large flares saturate the detectors, so the estimate is X13.)
Upper-level M-class flares and X-class flares can overload electrical power grids and cause black outs if operators do not take precautions. Satellites can be damaged or even destroyed when their electronics are saturated by charged particles from large flares.
Evidence of that is seen in SOHO images where streaks indicate hits by high-energy protons traveling near the speed of light. The noise will diminish as the proton levels decrease. The detectors are continually evaluated by ground controllers and refreshed by a process called a bake-out when the noise level is too high.
Meanwhile, Earth is awaiting the possible arrival of the coronal mass ejection from this event.
"If it arrives, it will be 24 to 48 hours later," Reichmann said. The uncertainty comes from not knowing exactly where it was aimed when it left the sun, or the shape of the interplanetary magnetic field which will help direct it.
"One of the earliest indications will be a brightening
in the aurora as seen by the Ultraviolet
Imager aboard the Polar spacecraft," Reichmann said. (MPEG movies of images
gathered by the UVI are made every
six hours.) Then again, it might miss the Earth altogether.