This article presents a method for modeling extended small celestial (ESC) objects, which are mainly cometary systems. Special attention was given to the possibility of analyzing their structure and physical properties in line with the modern theories of the Solar System’s formation suggesting a rather complicated evolutionary dynamics. Modeling and investigating the structure of different extended celestial objects advance our understanding of the general evolutionary processes that have taken place in the Solar System because all its objects are evolutionarily related. The isoline modeling (IM) method was tested on the real comet data and proved effective in assessing the activity of the processes that occur as ESC objects move in space. The IM method is particularly useful for studying long-period comets that, in many cases, cross the perihelion only once within a foreseeable period of human existence.