The figure above shows a concentration of comets where today's telescopes can observe. In clicking here, an animation of this image extended to beyond Pluto figure.
The number of known comets increases from year to year: large telescopes and automatic telescopes for the detection of asteroids (LINEAR, SpaceWatch, NEAT ...) detect comets increasingly tenuous. Moreover, the SOHO Space Telescope detects a large number of comets when approaching the Sun. Some fall and disappear into the Sun ...