Ten years after Rosetta final landing, Imperial researchers unlock new comet insights

New analysis from the European Space Agency’s Rosetta mission is shedding fresh light on the plasma environment surrounding Comet 67P.

On 30 September 2016, the European Space Agency’s (ESA) Rosetta spacecraft made a controlled descent onto the surface of Comet 67P/ Churyumov-Gerasimenko, bringing one of the most ambitious comet missions ever attempted to an end.

Rosetta was ESA’s landmark comet-chasing mission and the first spacecraft to orbit a comet and accompany it on its journey around the Sun. By travelling alongside Comet 67P for more than two years, it provided a unique view of how cometary activity evolves over time.

During its two-year escort of Comet 67P, the spacecraft collected a vast dataset on the comet’s composition, structure and interaction with the surrounding space environment.

Ten years later, data collected during the mission is still yielding new discoveries. A recent study published in Monthly Notices of the Royal Astronomical Society sheds new light on the complex plasma environment surrounding the comet, demonstrating the enduring legacy of the mission.

Imperial researchers played a key role in the mission. Scientists from the Department of Physics worked on the Rosetta Plasma Consortium (RPC), with Chris Carr acting as Principal Investigator.

Chris said “Imperial's Space Magnetometer Laboratory built the power and data-processing electronics which operated the 5 sensors of the RPC, which was designed to study the plasma environment around Comet 67P.”   

Using data from these instruments, scientists were able to track how the cometary plasma, the ionised part of the comet’s escaping atmosphere, or coma, evolved as the comet travelled from more than three times Earth’s distance from the Sun to its closest approach near Earth’s orbit and back again.

Scientists from the Department were also associated with ROSINA, the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, which studied the composition of gases released from the comet. The measurements revealed how the comet interacted with the solar wind and provided the most detailed picture of a cometary plasma environment over an extended period.

Despite Rosetta’s many discoveries, some questions remained about how charged particles behaved around the comet as its activity declined towards the end of the mission.

A decade later, new answers

The study revisited observations collected during the spacecraft’s final year at Comet 67P. The team combined Rosetta measurements with advanced simulations to investigate how charged particles behaved when the comet was releasing relatively small amounts of gas, a phase known as weak outgassing.

The research focussed on a poorly understood transition in the comet’s plasma environment that occurred after Rosetta’s final detections of a diamagnetic cavity, a region around the comet where the solar wind’s magnetic field is excluded. Previous models struggled to explain the observations recorded by the spacecraft during this period.

This study not only explains the observed ion dynamics but also provides a consistent thread that ties together all of the previous studies of Rosetta plasma observations under weak outgassing conditions. Victor Steinwand lead author of the study and a PhD student in Imperial's Department of Physics

By bringing together Rosetta observations and three-dimensional plasma kinetic and hybrid simulations, the researchers were able to identify how ions move and evolve around a weakly active comet and what the drivers are. The findings help explain observations that could not be interpreted when the mission ended in 2016 and provide a more complete picture of the interaction between the comet and its surrounding space environment.

Victor Steinwand, lead author of the study and a PhD student in Imperial's Department of Physics, said "This study not only explains the observed ion dynamics but also provides a consistent thread that ties together all of the previous studies of Rosetta plasma observations under weak outgassing conditions."

For researchers, the study highlights the lasting value of the mission’s dataset. Ten years after the spacecraft’s final landing, its observations continue to generate new scientific discoveries.

Professor Marina Galand, who leads the magnetometer on probe B2 of Comet Interceptor, said “The Rosetta mission returned an amazingly rich dataset of the cometary environment over a range of outgassing.

Exploiting this multi-instrumental dataset over the past years using physics-based models has allowed us to start building a self-consistent picture of the processes at play in this natural plasma laboratory.”

Looking to the future

Rosetta’s legacy also lives on through the next generation of comet missions. Imperial researchers are now contributing to ESA’s Comet Interceptor mission, which will seek to investigate a previously unvisited and yet-to-be-detected comet entering the inner Solar System for the first time.  

Professor Galand added, “With a currently unknown target, it is key to test our plasma models against the dataset returned from past cometary missions, such as Rosetta, and improve an understanding of the solar wind-comet interaction over a range of outgassing. A magnetic-field free region, formed around the cometary nucleus, remains however, so far, largely a puzzle, which probe B2 may be able to help solve”

Building on expertise developed through Rosetta, the mission promises to provide another opportunity to study some of the most primitive material left over from the formation of the Solar System.