The interaction of unmagnetised objects with the solar wind is of major interest to plasma physics and planetary formation and evolution. Understanding the processes at play will enable a deeper understanding of the way planetary atmospheres and magnetospheres work at a variety of objects. Two of the best studied unmagnetised objects are Mars and comets (67P/Churyumov-Gerasimenko in particular) where a large variety of boundaries and regions have been investigated in the last decades.

In particular the last years have brought large advancements in knowledge due to the MAVEN and Rosetta missions. However the similarities between these two fields and teams of scientists have not been explored sufficiently. The aim of this ISSI team is to bring together experts from the Mars and cometary plasma fields to profit from the different points of view and areas of expertise. We aim to investigate three main topics:

1. Which boundaries and processes exist at both Mars and a comet and what are their common properties?

2. The diamagnetic cavity at a comet has been studied in detail, but many questions remain unanswered. What does a field-free region like this look like at Mars?

3. Mars atmosphere and ionosphere change with orbital changes. How are these changes related to the changes in the plasma environment of a comet?

Answering these questions will help to better understand both Mars’ and a comets plasma environment and advance our knowledge on plasma physics and planetary evolution.