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The Big Questions
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The Sun's outer atmosphere (the Corona) is hotter
than 1,000,000°C (1,800,000°F) while the visible surface has a
temperature of only about 6000°C (10,000°F). The nature of the processes that heat the
corona, maintain it at these high temperatures, and accelerate the
solar
wind is a third great solar mystery. Usually temperatures fall as you move away from a
heat source. This is true in the Sun's interior right up to the visible surface. Then,
over a relatively small distance, the temperature suddenly rises to extremely high values.
Several mechanisms have been suggested as the source of this heating but there is no
consensus on which one, or combination, is actually responsible.
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Areas on the Sun near sunspots often flare up, heating material to
millions of degrees in just seconds and blasting billions of tons of material into space.
The precise causes of solar flares and coronal
mass ejections is another one of the great solar mysteries. Here again, we now know
many details about these explosive events and we understand the basic mechanisms, but many
details are missing. We still cannot reliably predict when and where a flare will occur or
how big it will be. This problem is a little like trying to predict tornadoes.
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Over about 11 years the number of sunspots
seen on the Sun increases from nearly zero to over 100 and then decreases to near zero
again as the next cycle starts. The nature and causes of the
sunspot
cycle constitute one of the great mysteries of solar astronomy. While we now know many
details about the sunspot cycle, (and also about some of the
dynamo
processes that must play key roles in producing it), we are still unable to produce a
model that will allow us to reliably predict future sunspot numbers using basic physical
principles. This problem is a little like trying to predict the severity of next year's
winter or summer weather.
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The Sun should produce more than twice as many neutrinos than are
observed. These ghostly subatomic particles are released by nuclear reactions in the Sun's core. They then pass directly through the Sun and out
into space. Detecting neutrinos is difficult, but the results from several independent
experiments now confirm that only about a third of the expected numbers are counted here
on Earth. Solar astronomers have attempted to alter their models of the Sun and its
evolution over the last 4.5 billion years to make a model of the Sun that produces fewer
neutrinos. These attempts have proven to be unsuccessful. This has led many scientists to
question our understanding of neutrinos themselves. This final mystery may thus shake some
of the foundations of Physics itself.
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June 5, 1998 - Neutrinos have mass! see:
http://www.phys.hawaii.edu/~jgl/neutrino_news.html
For more on neutrinos see:
http://www.physics.helsinki.fi/neutrino/
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