In December 2021, ESA called for proposals for the next M-class mission, pencilled in for launch in the mid-2030s. From 27 responses, experts within and outside ESA used rigorous scientific and technical assessments and a peer review selection process to narrow down the number of proposals in the running. In November 2022, five mission concepts remained.

Between January and September 2023, these final five went through ‘Phase 0’ studies – an undertaking that explores the expected science that could be achieved with each mission, as well as coming up with a preliminary mission design.

Today, ESA’s Science Programme Committee endorsed the decision that three of the five – M-Matisse, Plasma Observatory and Theseus – will enter a more detailed study period (Phase A) to continue exploring their potential. More information about the science goals of each mission can be found at the end of this article.

“All five mission proposals that went through Phase 0 were excellent – they addressed unique and exciting topics, and were achievable in the mid-2030s timeframe, so it was really difficult to come to a final decision,” explains ESA Director of Science, Carole Mundell.

“We established a panel of experts from ESA Member States to review the candidate missions. The reviewers followed a strict selection process, which included looking at science value, scientific feasibility, timeliness and complementarity with other projects.”

Cecilia Hernández of AEE (Agencia Espacial Española), Spain, Chair of the Science Programme Committee, adds: “We would like to congratulate all five proposals, each of which showed excellent promise to shed light on unanswered space science questions. We look forward to the many discoveries that will be made by the final selected mission.”