UCL Astrophysics Group


Professor Nick Achilleos awarded medal for Jupiter and Saturn discoveries

16 January 2023

Astrophysicist Professor Nick Achilleos has been awarded the 2023 Chapman Medal from the Royal Astronomical Society (RAS) for his outstanding work advancing understanding of the magnetic bubbles (magnetospheres) of planets, in particular Jupiter and Saturn.

Prof Nick Achilleos

The award citation noted his investigations use numerical modelling of the forces at play in planetary magnetospheres – regions of space around a planet where its magnetic field dominates.

Through these investigations, Professor Achilleos discovered that hot plasma significantly altered the disk-like shape of Jupiter and Saturn’s magnetic bubbles, helping to better match theoretical models with observational data recorded by NASA’s Cassini spacecraft. He also found, contrary to previous understanding, that hot plasma pressure significantly affected the environment around Saturn’s biggest moon Titan.

These discoveries were made using the UCL Magnetodisc Model – a numerical simulation of the immense centrifugal stresses, magnetic forces and plasma pressure present in rapidly rotating magnetospheres.

The citation also noted Professor Achilleos had encouraged wide community use of this model, making some of its outputs available to open access initiatives, the Europlanet Virtual European Solar and Planetary Access and Planetary Space Weather Services.

Nick, said: “It is a very surprising and welcome honour to be receiving this award. I share it with all of my colleagues at UCL and elsewhere who played a role in this work. I hope as a result we can attract more talented students and early career scientists to the field of magnetospheric plasma physics – they have been critical in advancing this field.

“I dedicate this award to my amazing mother, Georgia, whose sacrifices inspired me to reach for opportunities that she never had for herself. For their support in both good and bad times, I also thank my partner Kevin, my chosen family in the UK and my family in Australia.”

Each year the RAS recognises significant achievement in the fields of astronomy and geophysics through its awards, encompassing different types of talent from research to education and outreach. 

The Chapman Medal is awarded for investigations of outstanding merit in the science of the Sun, space and planetary environments or solar-terrestrial physics. This medal is awarded for a single investigation, or a series of closely linked investigations, of outstanding merit.

Professor Mike Edmunds, the President of the Royal Astronomical Society, said: “One of the best parts of my role as President is celebrating the remarkable talent in the astronomy and geophysics community. Our medals and awards honour the very best people in our sciences, marking both those with extraordinary promise at the start of their careers and those who have shaped our understanding of the Earth and the cosmos over decades. My congratulations to everyone!”



  • Courtesy of Professor Nick Achilleos