16 February: Saturn's aurorae are powerful light shows generated when charged particles flowing from the Sun hit the planet's upper atmosphere. These particles, known collectively as the solar wind, create similar effects on Earth.

Cassini has measured how the intensity of Saturn's aurora depends on the pressure of particles in the solar wind. This picture shows three Hubble Space Telescope images taken on 24, 26 and 28 January 2004. The strong brightening of the aurora on 28 January corresponds with a surge in the solar wind. Cassini also found an associated boost in radio-wave emissions from the planet's atmosphere. The results are described in three papers in this week's Nature.

Clarke, J. T. et al. Nature 433, 717-719 (2005);Crary, F. J. et al. Nature 433, 720-722 (2005);Kurth, W. S. et al. Nature 433, 722-725 (2005).