Being the closest planet to the Sun gives Mercury a certain charm and its composition is as interesting as you might expect from its unique location. Its perilous atmosphere consists of a mixture of sodium, helium, potassium, oxygen and hydrogen. Although its surface is hard and rocky (unlike some gas giants elsewhere in the solar system), the so-called exosphere is not breathable at all.
Mercury, also the smallest of the eight planets, boasts crater-filled landscapes that call to mind another iconic resident of the solar system: Earth’s moon. However, lone Mercury does not have any moons of its own. He’s not the only one with this unique property – the flower doesn’t have one either. In fact, other than the planet Pluto has eight moons that it calls its own moons. So why not Mercury?
The many moons of the solar system
The planets of the solar system acquired their moons in different conditions. Earth’s solitary moon is believed to have formed when another body hit the planet. The force of such an impact would separate the small pieces which would then combine to form Neil Armstrong’s famous stomping ground.
Further in the solar system regions Jupiter, Saturn, Uranus and Neptune formed like miniature solar systems. Far from the sun’s immense gravitational pull, cold shards of gas and ice formed these vast planets, and the rest are believed to have become multiple moons. Saturn has the largest number of moons in the solar system: 82, although 29 of them are called temporary moons before further study.
Mercury, for its part, is a terrestrial planet, which means that it has the hard surface characteristics of those worlds closest to the Sun. It appears to lack any moons due to its close proximity to the most famous stars.
gravity
Mercury is about 66 million kilometers from the sun. This is a mind-boggling distance. But in terms of space, they are next door neighbors. Of course, this means that the extremely hot and dense star has an incredible amount of influence on Mercury. Since it is slightly larger than Earth’s moon, Mercury’s gravity is relatively low. As a result of this and the Sun’s gravity, the tiny planet (which is about the size of the United States, and has a diameter of 4,878 kilometers) will not be able to dominate any moons that have evolved. The sun will cut off its orbit and block it.
Venus, which also has no moons, is a slightly different case. At four-fifths the size of Earth, it would normally be able to keep any moons in orbit. Venus is believed to have had a moon at some point in the solar system’s long existence. However, they are much closer to that pesky life-giving Sun than we are, so any potential moons would be pulled away.
Reem El Shazly
1 comment
The simple reason for Mercury’s lack: its Roche Limit, where any moon would be so close to the planet it would be pulled apart, and its Hill Sphere where any moon would be pulled away by the sun’s gravity, overlap.
And Pluto only has five moons, not eight. See my book “Moons of the Solar System; revised second edition”