Presence of planets in Milky Way and other galaxies Are there only planets in the Milky Way galaxy, or are there other planets in other galaxies? 
If planets are only in the Milky Way, why aren't there planets in others?
 A: Observing planets in other galaxies is really hard to do because they are so far away and planets are so small. One of our closest neighbors, the Andromeda Galaxy (also called M31), is about $10^{19}$ km away (just under 780 kpc), so finding a planet the size of Jupiter (roughly $10^5$ km diameter) is pretty tough (radius to distance is very small). Even the closer neighbors, the Magellanic clouds at distances of 50 and 60 kpc (LMC & SMC respectively), are still over $10^{18}$ km away so finding planets orbiting stars there are equally challenging.
It has been proposed that one can use microlensing to detect (large) planets orbiting stars. Some people have claimed to have found a star with an gravitational lensing aberration that could be the result of a planet. This is really a guessing game because the resolution is, at best, a few pixels on a CCD.
We do not believe that the Milky Way galaxy is unique in its development of planets, especially given the findings of the Kepler mission (prior to its failure) that there's roughly 1.6 planets per star. But we can't really say that there is indeed planets in other galaxies simply because we haven't had observations confirming the hypothesis.
