The polar lights known as
auroras are produced when charged subatomic Line particles, such as
protons and electrons flowing from the sun through Earth’s
magnetosphere, collide with atoms and molecules in Earth’s upper
atmosphere. For reasons not entirely understood,
magnetic storms, called substorms, (5) occasionally occur where the
flow of particles greatly increases and the
interplanetary magnetic field becomes much stronger. These substorms are
frequently visible on the Earth because they increase
the intensity of the polar lights.
Recently, five identical probes were blasted into orbit in a $200 million
US project known as the THEMIS mission. Scientists hope
the probes will be able to (10) investigate a number of mysteries about
the nature of the substorm instabilities, including when
and where substorms begin, how the individual components
of the substorm interact, and how substorms power the auroras. The
mission’s secondary objectives involve understanding and
predicting variations in the flux of electrons in
Earth’s outer radiation belt. These electrons pose a hazard to the (15)
safety of both astronauts and spacecraft. Understanding substorm
instabilities would thus improve success rates of future
space missions. The main purpose of the passage is to
A． explain why it is important to invest in space research B． explain how magnetic substorms interfere with satellite communications C． define magnetic substorms and identify a recent scientific experiment to study them D． compare two alternative approaches to the study of magnetic substorms E． demonstrate that unmanned probes are the best way to conduct research in space