Like water from a spinning lawn sprinkler, electrically charged particles in the solar wind spiral outward from the sun's corona in continuous streams. Hydrogen and helium make up about 99.9 percent of the wind, with a medley of heavy elements filling in the rest. Now, measurements from the Solar and Heliospheric Observatory (SOHO) satellite have provided the most detailed picture to date of these so-called minor elements, which carry major information about processes occurring in the sun's corona.

Antoinette B. Galvin of the University of Maryland in College Park presented data from the Charge, Element, and Isotope Analysis System (CELIAS), a group of instruments aboard SOHO that counts and evaluates particles in the solar wind.

Scientists recognized some of the chemical isotopes from previous satellite observations of the solar wind, but CELIAS also detected many that had not been reported there before. These include isotopes of silicon, sulfur, calcium, chromium, iron, and nickel. Isotopes of neon and argon were measured by SOHO but not by earlier satellites, although they had been detected in solar wind during the Apollo lunar landings more than 20 years ago, Galvin says.

Compared to instruments on previous satellites, SOHO's mass spectrometer collects more particles and can distinguish more accurately between them. This power enables the scientists to see the detailed time distribution of isotopes. "Before, we'd just grossly average over days or months," Galvin says. "Now, we can do it on a time scale of hours, occasionally minutes, so we're getting structures we didn't see before. It's very new and exciting."

The isotopes provide clues to where the solar wind originates, indicating how particles move to the corona from the sun's surface and the temperature in the corona, Galvin says.

Right now, most of the solar wind is coming from coronal holes, or openings in the sun's magnetic field, but later in the year, the scientists expect coronal mass ejections (SN: 2/1/97, p. 68) to step up. "There will be a lot to show with time," Galvin says.