There is no doubt that the Rosetta space mission captured the public’s imagination. Rosetta was the first spacecraft to orbit a comet, the first spacecraft to fly alongside a comet, and the associated Philae lander performed the first soft landing on a comet. The Rosetta mission ended in September 2016 with a controlled impact onto comet 67P/Churyumov-Gerasimenko, which it had been investigating for more than two years.

Shortly before this, a discussion meeting was held at the Royal Society to examine the results of the mission and the implications for cometary and solar system science in general. The latest issue of Philosophical Transactions A brings together papers from the meeting to provide a comprehensive summary of the ground-breaking discoveries from Rosetta, placing them in the context of cometary science as a whole. The issue was guest edited by Geraint Jones from University College London’s Mullard Space Science Laboratory alongside Matthew Knight from the University of Maryland, Alan Fitzsimmons from Queen’s University Belfast and Matt Taylor from the European Space Agency.

Comets are believed to provide scientists with a direct insight into the conditions that existed in the early Solar System. Since the first cometary mission in 1985, several probes have been launched to study comets directly, but “Rosetta was the most ambitious and sophisticated cometary space project yet attempted”, explains Jones. “The mission’s observations provide our first in situ record of the changing nature of a comet’s nucleus and coma over an extended period, complementing the ‘snapshots’ of comets provided by other targeted missions. This wealth of information should lead to great steps forward in our understanding of comets, and hence the conditions prevalent in the early Solar System”.

The collection of papers opens with a review looking at what we knew about cometary science before the Rosetta mission. The following papers go on to examine various aspects of the mission, including a summary of the mission operations, an analysis of the composition of cometary ices, the interaction of the solar wind with comets, and analysis of cometary dust particles. Michael A’Hearn from the University of Maryland brings the volume to a close by looking at ahead at the questions about cometary science that still need to be answered. “This is an exciting time for cometary scientists,” he concludes. “As we have dramatically increased our knowledge, we have also opened up many new questions. It is important that agencies focus on projects that lead to a better understanding of the important questions that drive cometary science”.

The Guest Editors were greatly saddened by the passing of Michael A’Hearn, whose death coincided with the publication of these papers. In view of his major contributions to the field of cometary science over several decades, all pursued with great enthusiasm, the Guest Editors wish to devote this collection of papers to his memory.

This issue will be free to read until 12 June and will also be available to buy in print.