At this scale, light requires a little over a month to cross the picture. The orbit of Pluto lies at a distance of less than 6 light hours from the Sun so we are still roughly 100 times further from the Sun than Pluto. Hence the dot in the center is still a bit larger than the entire solar system. The average distance from the Sun to Earth, about 150 gigameters (150 000 000 000 m), is called the astronomical unit (ua). This picture is over 6500 ua across.
We are still within the Oort Cloud of comets, chunks of rock and ice orbiting the Sun very slowly in random directions. The largest of the proto-comets is at most a few kilometers wide. To account for the number of comets reaching the inner solar system, it is estimated that there may be as many as 1011 (100 thousand million) of them. The total mass of the cometary halo is thought to be only 1/10 to 1/100 of the mass of Earth.
Copyright © 2016 by Bruce Bryson