This past year solar astronomers got their answer to the Hubble Space Telescope: soho, the Solar and Heliospheric Observatory, launched in December 1995 by the European Space Agency and nasa. The billion-dollar satellite has now settled comfortably into orbit around a point 1 million miles from Earth, where our planet’s gravitational pull and the sun’s and the centrifugal force on the spacecraft are exactly in balance. From that privileged location soho can stare at the sun 24 hours a day, measuring everything from the temperature of the corona (3.6 million degrees) to vibrations caused by sound waves inside the sun--the solar equivalent of earthquakes. The latter measurements have already forced researchers to reconsider their picture of how the sun’s roiling outer layers carry heat to the surface. Instead of rising in giant convection cells that reach deep into the sun, as had generally been assumed, the hot gas seems to flow through a series of thin cells that are stacked like pancakes under the surface, five to ten deep.
Even in the middle of a quiet period in the sun’s cycle of activity, soho has been able to pick out jets and storms that would have been undetectable from Earth. You can see the dynamics--explosions and little jets all over the place, says astronomer Art Poland of nasa’s Goddard Space Flight Center. Even just seeing the surface of the sun bubble around tells you a lot. It’s really a wild place.
