How can the Hubble Space Telescope (HST) take pictures of objects light-years away but not get a good picture of Pluto?

Pluto is very small. At its distance, it subtends a smaller angle on the sky than does a galaxy at a distance of billions of light-years. Consequently, even HST cannot resolve the planet's surface very well, because that would require a resolution of better than about 0.1". Still, HST has produced a spectacular image of Pluto and its moon Charon. — DANIEL CHRISTLEIN, UNIVERSIDAD DE CHILE AND YALE UNIVERSITY