What are the Planets that Have No Natural Satellites called?

The planets that do not have natural satellites are called Mercury and Venus. A natural satellite is a smaller celestial body that orbits a planet. Satellites are usually smaller in size than the planet they orbit. These planets are usually found, in turn, orbiting a parent star.

In our solar system there are 6 other planets apart from Mercury and Venus, which do have natural satellites. They are Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The only natural satellite of the Earth is called the Moon, however, this term is accepted to refer to any natural satellite of another planet.

Planets that do not have natural satellites

There are several theories about why Mercury and Venus do not have natural satellites, although the most accepted is that their sizes are the main reason.

The 4 planets closest to the sun, Mercury, Venus, Earth and Mars, are significantly smaller than the rest of the planets in the solar system..

This would imply that during their formation (as planets) there was not enough mass to form 2 celestial bodies so close. 

It makes even more sense if we take into account that the Earth's satellite is the product of a collision with a protoplanet, and those of Mars are practically taken as asteroids..

Mercury

It is the planet of our solar system closest to the sun, it is part of the inner or terrestrial planets, whose main characteristic is the abundance of silicates.

This means that it has a solid surface, unlike the gaseous planets like Jupiter or Saturn, made up mainly of hydrogen and helium in various states..

Mercury has no natural satellites and is the smallest planet in our solar system. Its proximity to the sun means that it has extreme temperatures, being this of more than 300 ° C during the day and -170 ° C during the night.

Its geology has numerous craters and a lot of erosion. In general, the conditions of Mercury are extreme (especially the temperatures), therefore it is normally described as a planet "where human life would be impossible".

Venus

It is the second closest planet to the sun. Like Mercury, it is an inner planet, so it has a solid Earth's crust.

It is occasionally compared to the Earth for the common characteristics they share in terms of composition and size, with our planet being slightly higher in mass and volume..

Despite sharing certain physical characteristics, Venus has very different environmental conditions..

One of the most peculiar is the composition of its atmosphere, which has many greenhouse gases, which raises the average temperature of the planet to more than 400 ° C. It is the hottest planet in our solar system despite not being the closest to the Sun.

Planets that do have natural satellites

Excluding Mercury and Venus, all the other planets in the solar system have at least one satellite or moon..

By observing what the known satellites are called, it can be seen that they all bear names belonging to different world mythologies, except for Uranus, whose moons are named after characters from works by William Shakespeare.

The planet with the most known moons is Jupiter, with a total of 69. The largest moon in the solar system is located precisely on Jupiter and is Ganymede, with a larger size than the planet Mercury.

References

1. About the Moon (s.f.). Retrieved on October 4, 2017, from Nasa.
2. Moons Of The Planets (s.f.). Retrieved on October 4, 2017, from Go Astronomy.
3. Phillips Davis (s.f.). Venus: Overview. Retrieved on October 4, 2017, from Nasa.
4. Kim Zimmermann (June 15, 2016). Ganymede: Facts About Jupiter's Largest Moon. Retrieved on October 4, 2017, from Space.
5. All About Mercury (July 7, 2016). Retrieved on October 4, 2017, from Nasa.
6. Sandra May (March 30, 2011). What Is the Planet Mercury? Retrieved on October 4, 2017, from Nasa.