There isn't two there is four Jupiter Saturn Uranus and Neptune.
do the densities of the solar system planets fall into two or more groups
Saturn is most famous for having rings. You can even see them with a simple telescope. Other planets have rings. Neptune, Uranus and Jupiter do, though their rings are much hard to see that those of Saturn.
Mars and Earth
In our solar system, Mercury and Venus are the two planets which do not have moons.
Two of them
Jupiter and Saturn
Mercury and Venus
rock and gas
Neptune and Uranus
Uranus and Venus are the two planets in our solar system that have a retrograde rotation. All of the planets orbit the Sun.
There are two types of planets in the solar system. These are, the smaller, rocky planets, which are Mercury, Venus, Earth, and Mars, and the gas giants, which are Jupiter, Saturn, Uranus, and Neptune.
The answer is there are two planets which have no moons. Venus and Mercury