Uranus has 5 large moons as well as 10 smaller ones that were discovered by the Voyager 2 probe. [1], A gas dwarf is a gas planet with a rocky core that has accumulated a thick envelope of hydrogen, helium, and other volatiles, having as result a total radius between 1.7 and 3.9 Earth radii (1.7–3.9 R⊕). Had the search for the planet taken place a few years earlier or later it would not have been found anywhere near the predicted location. There are several Web sites that show the current position of Neptune in the sky, but much more detailed charts will be required to actually find it. google_ad_width = 120; Since we lost Pluto as an official planet, it appears that Mercury is now considered the smallest planet in the solar system. Neptune is the fourth largest planet in the solar system. So, the smallest “mini gas giants” are around 1.3–1.4R, 3.5–4M (Earth units). In fact it would be considered the second smallest planet.