The classical view that comets do not evolve while they are stored far from the sun in the Oort cloud and Kuiper Belt began to change as far back as the 1970s, but the pace of discoveries about the way comets evolve picked up considerably in the 1980s and 1990s.As a result of these findings, astronomers now better appreciate that comets, though still the most pristine bodies known, have been modified in several important ways since their birth,says Stern.The realization that comets evolve during their long storage in the Oort cloud and Kuiper Belt provides insight and context to more confidently evaluate the results of astronomical and space mission observations of comets. So, too, it suggests that cometary sample return 16 missions now on the drawing board for NASA should employ relatively deep subsurface sampling if truly pristine, ancient material is to be collected.
