Mercury and Venus are the only two planets in the solar system without moons. It remains a mystery why the two lack moons but astronomers have ruled out mere coincidence.
Reasons Why Venus Has No Moon
Some have suggested that the absence of natural satellites around the planets is because of their proximity to the sun. Venus and Mars are not only exposed to extreme solar radiation but also experience high gravitational pull from the sun. The closer the objects in space, the higher the gravitational force between them. In this case, the sun is likely to pull any debris from Venus and Mars because it is significantly bigger and holds more mass.
A more recent model suggests that Venus might have had a moon in the past, but it was destroyed. The Earth's moon was formed when a rogue planet collided with Earth during the early stages of formation of the solar system, hurling debris into orbit. Typically, the material falls back to the surface of the planet but the impact distorted Earth's shape and its gravitational field resulting in lopsided gravity that allowed debris to remain in space. The material coalesced over millions of years and gave birth to the moon. Presumably, Venus also collided with an interstellar body that was either not large enough to distort Venus' gravity, and everything fell back to the surface of the planet or its moon just drifted away over billions of years.
Moons On Other Planets
Earth has one moon; the least of all the planets with moons.
Mars has two moons, the larger Phobos orbits 3,700 miles above the surface and takes three days to complete a revolution around Mars while the much smaller Deimos orbits at 14,573 miles and takes 30 days to complete a revolution. Phobos is spiraling inwards at a rate of 6 feet a century and will crash into Mars in 50 million years.
Jupiter has 79 known moons, the most of any planet in the solar system, but astronomers believe there are many more yet to be discovered. The well-known moons are Europa, Callisto, Io, and Ganymede, which is the largest moon in the solar system. The moons of Jupiter are large enough to be seen by amateur telescopes from Earth.
Saturn has 62 moons of which 53 have been confirmed and named while nine are awaiting confirmation of whether they are moons or asteroid trapped in the planets orbit. Titan is Saturn's largest moon and the second largest after Jupiter’s Ganymede. It is the only other place other than Earth in the Solar System where matter can exist in liquid form on the surface. It is also the only moon with an atmosphere.
Uranus has 27 known moons some of which are made of ice while Neptune has 14 known moons.