Question

what could be explained from the straing horizontal line observed at the begining and end of the graph

Answer 1

The head of the comet and the beginning of its long tail are shown. ... Comets are icy bodies in space that release gas or dust. They are often compared to dirty snowballs, though recent research has led some scientists to call them snowy dirtballs. Comets contain dust, ice, carbon dioxide, ammonia, methane and more.