CassiniHuygens will truly be the benchmark against which all future space missions are compared

After almost twenty years in space, the Cassini spacecraft will tomorrow (15 September) make its final encounter with Saturn, ending humankind’s first detailed exploration of the ringed planet.

For 13 years, Cassini has been sending back to Earth images of its extraordinary discoveries at Saturn.

Cassini’s Grand Finale is the ambitious culmination of a mission by a nuclear-powered robotic explorer that has travelled a total of 4.9 billion miles, completing 294 orbits of Saturn, with 360 engine burns, 2.5 million commands executed and 635GB of science data collected.

Planetary Scientists from our University have played key roles in the mission since the 1990s, and Cassini’s breath-taking discoveries have helped shape Leicester’s research into planetary magnetospheres, ionospheres and atmospheres since the robotic explorer launched in 1997.

These unprecedented findings have helped to inspire and launch the career of many young scientists, including Dr Leigh Fletcher from our Department of Physics and Astronomy, who speaks fondly of the pioneering space mission and his involvement in the project.

“The most important credential that this mission can be proud of is its international nature,” Leigh says. “27 nations, including the UK, were involved in this fantastic mission. Cassini-Huygens will truly be the benchmark against which all future missions are compared.”

Leigh works closely with University of Leicester colleagues, including Professors Stan Cowley and Emma Bunce, who are co-investigators on the magnetic field experiment on the Cassini spacecraft. Leigh is co-investigator on the thermal infrared instrument of Cassini (CIRS), and members of the Department of Physics and Astronomy have been involved in analysing data from Cassini’s ultraviolet, infrared and plasma instruments. 

This week, postdocs and students from our University are using observatories in Hawaii and Chile to support the mission in its final moments.

Together, the team of Leicester scientists have had significant involvement in the space mission for almost three decades, back to the first instrument proposals in the early 1990s and Cassini’s launch in October 1997.

On Saturday 9 September 2017, Cassini executed its final dive between Saturn and the rings, skimming just 1680 km above the clouds. Then on Monday 11 September the final distant encounter with Titan slowed the spacecraft sufficiently to force Cassini into its final orbit.

Between 13-14 September, Cassini assembled its final picture show, including colour mosaics of Saturn and its rings, a movie of Enceladus setting behind the northern limb of Saturn, and observations of tiny moonlets within the ring system – powerful images that will be remembered fondly by the team that captured them and will be used by scientists to learn more about the mysterious distant planet.

Tomorrow, on Friday 15 September, Cassini will cross the orbit of Enceladus one final time. It is expected that Cassini will begin to tumble around several axes, such that the high gain antenna is no longer locked on Earth.

“It will continue to fight, its fault-protection systems trying in vain to stabilise the spacecraft, but within seconds the high loads on the spacecraft will start to destroy structural components,” Leigh explains.  “The spacecraft will break apart, burning up like a meteor and melting, the individual materials dissociating so that the debris forever becomes a part of Saturn.”

Tomorrow, Leigh will be discussing Cassini with the media and members of the public, giving lectures and a Q&A in the Live Space gallery at the National Space Centre from 11am onwards, as well as offering insights as enthusiastic people worldwide watch the livestream from NASA TV during Cassini’s final moments (11:30-12:00) and during the loss of signal (12:55 BST).

Leigh will also be interviewed about Cassini by BBC Radio Leicester on Friday 15 September and he has recently conducted interviews on BBC Breakfast and The Sky at Night.

“This has been a bittersweet week, watching as my Cassini colleagues gather for the final time to watch the end of this 20-year journey,” Leigh says. “This heroic spacecraft has done everything we’ve ever asked of it, even fighting with its last moments to deliver new scientific insights back to Earth.  So although I’m sad that Cassini’s exploration will now be a part of the history books, I think we can be proud of everything that this mission has accomplished.

“It just shows what wonders can be achieved when 27 nations work together.”

Stanley Cowley, Professor of Solar Planetary Physics, from our Department of Physics and Astronomy, said:

“The Cassini mission to Saturn has represented a massive chunk of my scientific career, having originally been involved in the successful bid to NASA to build its magnetic field instrument when working as Professor of Physics at Imperial College in 1990.  Since moving to Leicester in 1996 Cassini-related work has been a central part of my research programme, consisting of both data analysis and related theoretical studies, leading to the publication of over a hundred research articles in international journals and the training of a dozen doctoral research students.

“Our work has focused on the magnetic effects of the electric currents that flow in Saturn’s outer environment, figuring out the physical origins of the mega-amp currents that flow around Saturn in the equatorial plane, making the first observations of the polar currents that light up Saturn’s polar auroras, and characterizing the weird oscillations in the gas and field near the ~11 hour planetary rotation period that pervade Saturn’s outer regions.

“It will be sad to see Cassini go on Friday, especially as the instrument we built is still working perfectly after 20 years in space, but we recognise that it is important to bring the mission to an end in a tidy and controlled manner.”

Emma Bunce, Professor of Planetary Plasma Physics, from our Department of Physics and Astronomy, said:

"My involvement in the Cassini mission began not long after the end of my PhD work in around 2002. My PhD supervisor Stan Cowley was a Co-Investigator on the Imperial College led magnetometer (he still is, and I am too now), and he decided it was time to switch our attention from Jupiter to Saturn around that time. We started to work on the magnetometer data from interplanetary space as Cassini made its long journey to Saturn.

"From there, I was welcomed into the team and have worked on many aspects of the structure of Saturn’s magnetosphere and nature of the aurora in the upper atmosphere since that time. The unprecedented data from the Cassini mission has enabled the magnetometer team to make many amazing discoveries about the Saturn environment, and we still have much to learn from the Grand Finale orbits which we will be analysing for months to come.

"I owe a great deal to this mission, and I am so grateful for the opportunity to have been involved – in the lifetime of Cassini my career has progressed from new post-doctoral researcher to Professor and a significant fraction of that progression is owed to the fact that I was given the opportunity to be part of this fantastic team."

The BBC's live coverage of Cassini highlighted the University of Leicester team

Watch Dr Leigh Fletcher's interview with BBC East Midlands here:


BBC Sky at Night feature with Dr Fletcher: