This is the headline in a couple of news sources – the leaky atmosphere of Mars. See for example https://phys.org/print437390658.html … is about the way Mars lacks a magnetic field of note and that is generally thought to be the reason why it has a thin atmosphere – most of it lost to space as a result of being buffeted by the solar wind. New data from ESAs Mars Express spacecraft shows how ionisation plays a prominent role in safeguarding the planet. Magnetic fields are thought to protect planets – but is this just an assumption that may be overstated. Magnetic fields deflect charged particles from the solar wind by creating a bubble, the magnetosphere. However, Mars may lack much of a magnetic field but it has an ionosphere – just like the Earth. It creates a region of electrically charged plasma. Observation has shown that increased ion production triggered by ultra violet solar radiation shields Mars atmosphere from the energy within the solar wind. The Sun's radiation produces more ions than cane be removed by the solar wind.
The same story is at https://tallbloke.wordpress.com/2018/02/09/leaky-atmosphere-linked-to-li… … but has the benefit of comments.