If I recall you should have an event that says who executed you or the reason you died (e.g. sunning). I doubt it was sunning by accident as I am sure you have to double confirm that in the same way as if you want to drop character.
Maybe check your events and see if they say anything.
You can fill out a support ticket. But there is nothing the system can do to you to actually kill you. It was intentional. You said you were on the ground then someone arrested you and then executed you. If this was on a Darkness planet you can appeal to have the death reversed.
If you were on the ground, then an arrest and execute is the only possible option. Atmospheric damage will never take you lower than 1hp IIRC, bandits and creatures don't attack you outside of Derra, and even other players cannot attack you as of yet.
That leaves only the possibility of an Arrest and Execute. It was an intentional kill.
Derra and Serocco also Dante as far as I know but regardless, as you stated they will only knock you to 1hp too. I concur with intentional arrest/execute. There are many who are willing to do this for no other reason than "they can", if you were outside of your ship on their planet...and it wasn't a Darkness or Quest planet.