A secondary atmosphere<span> is an </span>atmosphere<span> of a </span>planet<span> that did not form by </span>accretion<span> during the formation of the planet's </span>star<span>. A secondary atmosphere instead forms from internal </span>volcanic<span> activity, or by accumulation of material from </span>comet<span> impacts. It is characteristic of </span>terrestrial planets<span>, which includes the other terrestrial planets in the </span>Solar System<span>: </span>Mercury<span>, </span>Venus<span>, and </span>Mars<span>. Secondary atmospheres are relatively thin compared to </span>primary atmospheres<span> like </span>Jupiter's.<span> Further processing of a secondary atmosphere, for example by the processes of </span>biological life<span>, can produce a </span>tertiary atmosphere<span>, such as that of </span>Earth<span>.</span>
