What planetary attribute is required to hold onto a life-enabling atmosphere over cosmological timescales?

Answer

Sufficient mass, dictated by planetary size, leading to adequate gravity.

Planetary size determines mass and gravity, which are necessary physical characteristics for retaining an atmosphere over billions of years.

What planetary attribute is required to hold onto a life-enabling atmosphere over cosmological timescales?
astronomyplanetshabitable zonelifeHabitabilitygoldilocks zoneliquid water