We’ve said goodbye to Cassini. What comes next?
November 19, 2017

We’ve said goodbye to Cassini. What comes next?

Prof. Nick Achilleos (left), Anastasia Kokori (centre) and Dr. Patrick Guio (right) at UCL.

Article by Anastasia Kokori, who has participated in a Europlanet expert exchange programme with the department of astrophysics at UCL.

The Cassini mission, a collaborative effort between NASA, the European Space Agency, and the Italian Space Agency, said goodbye on the 15th of September 2017. The mission reached an end after 13 years of orbiting around Saturn, proving us with a large legacy of data that is still being analysed, and will keep scientists occupied for many years to come.

The research of the Planetary Plasma Physics Group at UCL focuses on the two gas giant planets of our Solar System, Jupiter and Saturn. The team, which currently consists of five members, studies the magnetic fields of these planets by applying models which help us better understand the observations made by spacecraft like Cassini.

Prof. Nick Achilleos highlights that one of the major discoveries of Cassini was the observation of water plumes erupting from Enceladus, the sixth largest moon of Saturn. Until Cassini arrived there, it was not known that Enceladus was a very geologically active moon.

“The discovery of water plumes in Enceladus, in essence, was a magnetometer discovery. Enceladus is considered to be a potential habitat for life. Now we know that the principal source of the material, known as plasma, in Saturn’s magnetosphere, are the plumes on Enceladus,” said Prof. Achilleos.

Artist’s impression of the Cassini mission at Saturn. Credit: NASA

Another question that Cassini is helping to address is why the magnetic and the rotational poles of Saturn coincide.

“In a magnetized planet, such as Saturn, physical theory says that we shouldn’t expect to see this phenomenon. This remains a mystery – although there are interesting theories as to why the planet’s field is so symmetric, some dating back to the Voyager era,” said Prof. Achilleos.

Space missions such as Cassini are also important for studies focusing on the phenomenon of space weather – the interaction between a planet’s magnetosphere and the solar wind. Saturn and Jupiter, like the Earth, are magnetized planets and their magnetic fields act as ‘umbrellas’ which mainly protect them from the solar wind. The magnetic field of our planet thus acts as a natural shield and protects us from much of the impacting material in the solar wind.

Dr. Patrick Guio explained, “Data from Space missions helps us understand how space weather affects engineering systems and infrastructure on the Earth, a new and important aspect of risk assessment and management.”

Prof. Achilleos added that the technology that is developed for pure science exploration and which is used in space missions, often finds practical application in other areas. In particular, he pointed out that, “Our job as scientists, and I think as a civilization, is to be curious about what we see and try to explain it. And when we do so, quite often what we find is that the science and the technology that we develop for this purpose, finds its way to other applications, so everything is interconnected in an unpredictable way.”

Cassini can be considered as a successful space mission that helped humanity investigate different aspects of planetary science and the Solar System in which we live. Now that we have a better understanding of the giant planet, Saturn, the question is what the next step will be.

JUICE (JUpiter ICy moons Explorer), one of our future space exploration projects, is the first large-class mission in ESA’s Cosmic Vision 2015-2025 programme, and is planned for launch in 2022. The UCL Planetary Plasma Physics Group is part of this effort through its participation with the JUICE magnetometer team. The mission will focus on Jupiter, the largest of the planets and has an even larger magnetosphere than Saturn – in fact, if we were able to see Jupiter’s magnetosphere in the night sky, it would have a similar size to our Moon.

JUICE will also fly by the moons Callisto and Europa, but the radiation environment particularly around Europa is very harsh, thus limiting the time it will spend there. The mission’s principal target will be Ganymede, Jupiter’s largest moon, which is also considered to be a potential habitat for life. Ganymede is the only moon in the Solar System that has a significant internal magnetic field of its own, but the field we have observed at Ganymede has contributions from many different sources. This is quite challenging for the magnetometer team, who are aiming to ‘tease out’ a small part of the complex field in Ganymede’s environment – specifically, the induced field which is generated by currents in Ganymede’s subsurface ocean. To help us attain this goal, JUICE will finish its mission by spending several months as a dedicated orbiter of Ganymede.

Despite the challenges, Prof. Achilleos highlighted that at the end of the day, “We try to understand reality by using models of reality, and improving our models and our understanding is a never-ending quest – particularly since space missions often raise just as many new questions as they answer.”

We stay tuned, waiting for missions such as JUICE to contribute to humanity’s efforts towards answering scientific questions, relevant not only to our giant planet neighbours, but also to our own home, the planet Earth.

This expert exchange has been funded through the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654208, Europlanet 2020 Research Infrastructure.