Exploring Unseen Depths of the Sun

Overview

The Sun is energized by the fusion of abundant hydrogen nuclei within a hot, dense core where the temperature rises to 15.6 million degrees. We know the sequence of nuclear reactions that occur down there, and have used models to describe how the energy is generated and works its way out by radiation and convection. There was one nagging problem involving neutrinos produced in vast quantities by the nuclear reactions. Massive underground instruments detected only one-third to one-half the number of neutrinos that theory said they should. The theoretical models have now been tested by directly probing the solar interior, showing that the neutrino calculations are not in error, so we seem to have an incomplete knowledge of neutrinos.

The inner structure and dynamics of the Sun are being studied by a new science called helioseismology. It uses observations of ripples or oscillations in the visible solar gases to detect low-pitched sound waves and thereby look deep down inside the Sun, in much the same way that an ultrasonic scanner can peer inside a mother’s womb and map out the shape of an unborn infant. Hehoseismologists have taken the temperature of the Sun’s energy-generating core, showing that it agrees with model predictions. This strongly disfavors any astrophysical solution for the solar neutrino problem.

Helioseismology instruments aboard the SOlar and Heliospheric Observatory, or SOHO, have shown how the Sun rotates inside, and suggested the internal location of the dynamo that sustains its magnetism. They have also described hot, gaseous rivers that circulate beneath the photosphere, detected internal tremors, or sunquakes, generated by flaring explosions in the corona, and discovered how to look through the Sun to observe active regions on the hidden back side of the Sun.