We tend to see the large planets farthest away from their stars. So it is unlikely we will find any small planets close to their star similar to Mercury.
Uranus
Mars The inner planets such as Mars, Earth or Mercury. these are too small to identify in other systems and too close to the star.
They least resemble rocky planets like Venus Earth and Mars, particularly they least resemble planets that we would consider as possible life sustaining planets.
We tend to see the large planets farthest away from their stars. So it is unlikely we will find any small planets close to their star similar to Mercury.
Mars The inner planets such as Mars, Earth or Mercury. these are too small to identify in other systems and too close to the star.
Jupiter
This question is impossible to answer. As of today, 11th April 2011, there are over 540 known extrasolar planets - each one is different in it's own unique way. The only answer, based on today's knowledge, is that none - so far - are like the inner planets but that is due to our technology rather than the actual planets.
Neptune is the most unknown since it's far away
It was not "found out" but a decision that was made by a panel of planetary experts to define what is a planet and what is not which "degraded" Pluto from planet status of "dwarf planet" on August 24, 2006.There are at least 44 dwarf planets known.
The planet with the least mass and smallest is Mercury. The planet with the lowest density is Saturn
Yes, Uranus is known to have at least 13 distinct rings. (see related question)
Jupiter has 63 known moons, followed by Saturn with 61. ( as of April 2009 ).