Solar Flares
You may have seen the "northern lights" in the fall of 2003, even if you live as far south as Texas or Italy. This energy in the sky originated in record-setting solar flares and coronal mass ejections triggered by the sudden release of magnetic energy near sunspots. The images show the flares and sunspots on October 28, 2003. These flares can equal one-tenth of the sun's total output, or, to put it another way, they can be as powerful as millions of large hydrogen bombs going off at once. The emitted energy is spread across the electromagnetic spectrum, from radio waves through gamma rays. The October 28 flare was followed by a record-breaker on November 4, which produced such intense radiation that the x-ray detectors on National Oceanic and Atmospheric Administration's satellites went off-scale for eleven minutes.
Movie of the coronal mass ejection (CME) on October 28, 2003. A disk blocks the light of the sun itself to make the CME visible. The “snow” at the end of movie is noise from the blast of charged particles from the sun. (image/movie courtesy of NASA)
The flares of October 28, in extreme ultraviolet light, along with the sunspots on that date. Compare the positions of flares and sunspots. (images courtesy of NASA).
In coronal mass ejections (CMEs), mentioned above, the sun belches forth vast amounts of matter—up to 10 billion tons of plasma (see Plasma Power). CMEs are often associated with solar flares, and the one that followed the November 4 flare is shown in the movie.
Even in its quiet state, the sun emits a constant stream of plasma called the solar wind, which fills space in the solar system. The solar wind and the CME—two plasmas—interact. The leading edge of the CME produces damaging high energy particles as it moves through the solar wind, even far from the sun. The Mars Odyssey spacecraft, more than halfway to its destination, was briefly disabled by these charged particles from the October 28 flare, and a radiation-monitoring instrument on the satellite has not recovered yet. Moreover, had astronauts been on the surface of Mars at this time, they would have been in great danger from the heavy dose of particle radiation.
The CME can also disturb Earth's magnetic field and produce damaging space weather effects, which can include communications problems and disruptions of electric power (see Space Weather). In addition, the high energy charged particles produced by the CME can be dangerous to spacecraft and astronauts. Two Japanese satellites were crippled by the October 28 flare, and numerous others had to be powered down into “safe mode” until the volley of particles had passed. On the other hand, Earth's magnetic field protects us by deflecting incoming charged particles, trapping them in orbits that extend along Earth's magnetic field lines, far above the surface (see drawing).
Charged particles trapped along a line of Earth's magnetic field. Note that the particle spirals in, reaches a minimum altitude, and is then reflected in the opposite direction. (image courtesy of NASA)
