Inverse square law
The Pluto system is about 40 times further away from the sun than the earth. So the available sunlight is 1/(40x40) = 1/1600 of the solar illumination on earth.
This is why photos and movies of astronauts on the moon or in spacewalks never show any stars. The stars are there all right, but you have to stop down the camera so much to get the astronauts that the stars don't show up in the picture at all. If you opened the shutter wide enough to see the stars, the astronauts and their surroundings would be totally overexposed: a featureless white glare.