A quintet of NASA science probes were launched February 17, 2007, on a two-year mission to better understand the shimmering auroras that light up the night sky near the Earth's poles.
  The unpredictable behavior of the aurora borealis, commonly known as the northern lights, has perplexed scientists for generations.
  Decades of research have revealed the spectacular phenomenon is caused by charged particles that stream from the sun. Known as the solar wind, the particles collide explosively with atoms in Earth's upper atmosphere.
  Magnetic fields that ring our planet capture the particles and carry them to the polar regions to form the multicolored curtains of light. But while auroras are increasingly well understood, a major mystery remains...