At some time in the next year or so, the space probe Ulysses will become
the first man-made object to pass over the poles of the Sun. By 12 October
it had already reached 37degrees south and was 3.95 astronomical units from
the Sun. Ulysses’ visit to the Sun, which involves scientists from 12 countries,
will be the grand finale of the first of two space explorations that have
both astronomers and physicists on the edge of their seats. The second is
much closer to home. At the end of 1995, the European Space Agency will
launch its four Cluster spacecraft, packed with identical instruments, which
will orbit the Earth as a group. They will be at the corners of an imaginary
tetrahedron, some 1000 kilometres apart.
These two missions will investigate some of the strangest places in
the Universe – the plasma that surrounds the Earth and the Sun. In these
regions of space, which are up to 100 or so times the radius of the Earth
or Sun, charged particles (ions and electrons) are accelerated to unheard
of energies, by moving magnetic fields. By investigating how they differ
from each other and from plasmas created in fusion experiments on Earth,
physicists aim to answer some big questions. How are particles accelerated
to such high energies? Is there a better way of controlling plasmas on Earth?
Ulysses’s mission encompasses more than a study of plasmas, however.
Its task is to make a pioneering exploration of the vast region of the Solar
System that lies outside the ecliptic plane – the plane in which the Earth
and planets orbit around the Sun.…
