A PASSION FOR SPACE
The Sky at Night presenter recaps her Cassini highlights as the probe begins its Grand Finale
The Cassini spacecraft is on a mission that keeps giving. Originally it was due to be operational for just four years, but it gathered so much data during that short time that it was extended to a whopping 13 years. All good things must come to an end, however, and on 15 September 2017 Cassini will be crashed into the planet it has been observing for so long. Its seems a fitting end: even in its death throes the spacecraft will be collecting information about the amazing Saturn system.
The Cassini-Huygens space probe was launched in 1997 and made a journey of 3.5 billion km to rendezvous with Saturn. The combined spacecraft went into orbit around the planet in July 2004. In December that year the Huygens lander, made by ESA, was released and touched down on the surface of Saturn’s largest moon Titan. This set the record for the farthest landing from Earth that a spacecraft has ever made.
Since then our knowledge of Saturn and its moons has been transformed. My top five highlights of the mission so far are:
When Cassini launched from Cape Canaveral in 1997, we were aware of 18 moons in orbit around Saturn. Now, with observations from Earth and analysis by Cassini, many more have been found – perhaps as many as 62, ranging in size from larger than planet Mercury to about the size of a football stadium.
2) Titan has lakes and seas of liquid methane, replenished by rain from hydrocarbon clouds. The mission also provided evidence that Titan is hiding an internal, liquid ocean beneath its surface, likely composed of water and ammonia.
3) The particles that make up Saturn’s rings range in size from smaller than a grain of sand to as large as mountains. Cassini found that water jets from the moon Enceladus provide some of the material in Saturn’s E ring, a diffuse ring situated outside the main, bright rings.
4) Saturn’s moon Enceladus is a small, icy body, but Cassini revealed that a liquid ocean exists under its crust. Geyser-like jets spewing water vapour and ice particles from its underground ocean were also detected. Analysis of this water revealed the presence of organic material, molecular hydrogen. With its global ocean, unique chemistry and internal heat, Enceladus is now thought one of the Solar System’s most scientifically interesting destinations.
5) Analysis of Saturn’s poles revealed giant hurricane systems. At the north pole the system is hexagonal in shape. Enormous planet-engulfing thunderstorms sometimes erupt from Saturn’s atmosphere, affecting the climate of the planet for many years.
As the mission enters its Grand Finale, manoeuvres are becoming more daring and risky, with orbits taking the spacecraft to within 300km of the inner edge of the rings and through unknown regions that could bombard its instruments with dust. Even with just a few months left, Cassini still has the opportunity to transform our understanding and I for one can’t wait to see what it will reveal.