NASA’s Hubble Space Telescope is responsible for capturing some of the most detailed images of distant galaxies, but it isn’t particularly useful when it comes to photographing closer objects like Pluto and other trans-Neptunian objects in our solar system.
As it would seem, this has to do with the angular diameter of the object in question. The size and distance of the said object are incredibly significant factors in determining Hubble’s ability to view it clearly. Pluto is much closer than any galaxy, but it’s also insignificantly tiny, which makes it tougher to focus on. Galaxies, although much farther away, are massive.
One of the best photographs ever taken of the Andromeda galaxy was resolved with the Hubble Space Telescope, and it’s comprised of several smaller photographs because the galaxy is so large that the whole thing wouldn’t fit in Hubble’s viewfinder.
The next time you wonder why Hubble can’t photograph Pluto as clearly as it can galaxies, or even larger planets, remember that it has to do with Pluto’s size and distance relative to our location in the Solar System.