Why Is Venus Hotter Than Mercury? Understanding The Solar System

The sun and objects that orbit it makes up the solar system. Of these objects, planets are well known and have been under research for a very long time.

Scientific research has brought about many theories and experiments. From this research, the scientists have come up with various conclusions.

That helps us to understand these bodies that orbit around the sun better. Amongst these planets, there exists Venus and Mercury.

Venus is the second nearest to the sun in our solar system. On the other hand, Mercury is the smallest in size of all the planets, and it is closest to the sun.

Following several mathematical calculations and experiments in physics, it has been established that Mercury is only slightly larger than the moon.

The sun could appear thrice its size when compared to how it looks from planet Earth. Venus is the brightest object apart from the moon at night.

This article is about the temperature of the planets Venus and Mercury. It will also touch on another planet in the solar system to help you understand it better. So let’s get back to the question.

Why is Venus hotter than Mercury?

Venus is hotter than Mercury because the atmosphere of Venus is denser than that of Mercury. Mercury has almost no atmosphere, whereas the atmosphere of Venus is thicker. 

The heat from the sun will quickly be radiated back to space for the case of Mercury; however, Venus will tend to trap the heat resulting in very high temperatures on its surface.

The Solar System

The term ‘solar system’ describes the planetary system which has our lovely planet EarthEarth. According to NASA (National Aeronautics and Space Administration), several planetary systems with planets orbiting a host star exists.

It is known as the solar system because of the sun, the host star, known as ‘solis’ in Latin. Anything that relates to the sun is then referred to as solar.

Some bodies are bound by the sun due to its gravitational pull. These masses in our solar system include planets, dwarf planets, dozens of moons, numerous comets, meteoroids & asteroids.

The planets that rotate around the sun include are Saturn, Earth, Uranus, Mercury, Venus, Neptune, Mars, and Jupiter. A familiar dwarf planet is Pluto.

The known moons which exist within the solar system are more than 200. Mercury and Venus are the first two planets of proximity to the sun. They are the only planets of all eight without moons.

The largest planets are Saturn and Jupiter. These two planets are known to have many moons. The popular Pluto has five moons, and even tiny asteroids do have moons.

The solar system’s formation is attributed to the ‘birth’ of the sun from a combination of hydrogen atoms to form helium. This releases a very high amount of energy in the process.

Gravity plays its part in smashing clumps of matter into one another. Thus, large bodies were big, and gravity played the role of shaping them into spheres. It’s the spheres that are now known as planets.

What Is The Role Of The Atmosphere In Planets?

The atmosphere is from Greek words that mean ‘vapor, steam’ and ‘sphere.’ It is a layer or layers of gases. These layers envelop a planet.

They are gases and could quickly diffuse away. Still, a planetary body usually has its force of gravity, which would hold these layers of gases, thereby retaining the atmosphere.

The atmosphere plays a crucial role in determining the temperatures and surface characteristics of substances found within a planetary body.

To understand the role of the atmosphere on planetary bodies and their composition and structure, we take a look at the Earth’sEarth’s atmosphere before discussing the atmospheres of both Mercury and Venus.


Earth’s atmosphere comprises layers of gases. Extensive studies have been done on the Earth’s atmosphere. Findings show that the planet earth has five different layers, each with other characteristics.

Earth’s atmosphere comprises seventy-eight percent of nitrogen, twenty-one percent of oxygen, and small percentages of argon and other gases.

About fifteen kilometers from the surface of the EarthEarth, we have the first layer, which is known as the troposphere.

Most of the substance that accounts for the entire mass of the atmosphere is found in the troposphere.

Dust, water vapor, and ash particles would mostly be found within this layer, explaining why most clouds are located. The other layers include the stratosphere, mesosphere, thermosphere, and exosphere.


The planet mercury is the nearest to the sun. It does not have an atmosphere but instead possesses a thin exosphere.

An exosphere is almost equivalent to an atmosphere. However, its density is so low that the molecules which are gravitationally bound to the body- in this case.

Mercury- is essentially collision-less. The exosphere of Mercury is made up of oxygen, sodium, hydrogen, helium & potassium.


Venus is Earth’sEarth’s closest planet and is similar in size and density to the EarthEarth. It has been labeled as Earth’s twin. Venus has a thick and toxic atmosphere.

This is because carbon dioxide gas is perpetually shrouded in thick, somewhat yellow clouds of sulfuric acid.

This immensely affects the air pressure at the surface. Scientists describe it as ‘crushing’ since it is estimated to be more than ninety times that of the Earth. This kind of pressure is similar to that which is a mile below the ocean on Earth.

The enveloping of the planetary bodies by these layers of gases exerts a force on the surface. This force is known as the atmospheric pressure and differs from one planetary body to another.

The atmospheric pressure is entirely dependent on the thickness and density of the atmosphere and the molecular substances that make up the gases present within these atmospheres.


Temperature is the degree of hotness or coldness of a body. The planets orbit the sun, which is the primary source of heat.

The presence of heat energy would consequently lead to a rise in the temperature of a given body. The solar system has its temperatures.

The study of planetary bodies within the solar system helps researchers obtain planets’ average temperatures.

The average temperatures of these eight planets and the dwarf planet, Pluto, in degrees Fahrenheit in their very order of proximity from the sun are as follows;

  • 800
  • 900
  • 60
  • -80
  • -238
  • -285
  • -353
  • -373
  • -387

The temperature always drops from one planetary body to another as the distance from the sun increases. Only Venus is an exception because of its extremely dense atmosphere.

Greenhouse Effect

After understanding the role, structure, and composition of the atmosphere and the relative surface temperatures of the planetary bodies, let’s look at the greenhouse effect.

The greenhouse effect comes in to help understand the correlation of the two parameters and how this relationship affects planets. The greenhouse effect determines energy flow in and out of planetary bodies.

Heat energy from the sun radiates to the surface of planets. The planets then release the energy into space; however, some atmospheric gases trap this outgoing heat.

This is a natural phenomenon that has aids the planet Earth to accommodate life. Without it, average temperatures on EarthEarth will be thirty degrees lower than the current fifteen degrees Celsius.

Greenhouse gases strengthen the greenhouse effect.  Some of these gasses are Water Vapor, Carbon dioxide, and many more.


On planet Earth, the combustion of fossil fuels and deforestation have led to increased greenhouse gases in the atmosphere.

This causes drastic changes in climate due to the increased amount of heat energy trapped within the atmosphere.

Most heat energy can longer escape to space, and surface temperatures have risen over the last century. Icebergs are melting, and the level of ocean water keeps growing.


The Venus atmosphere is thick, and it consists mainly of carbon dioxide. This major component of the Venusian atmosphere is a greenhouse gas.

This means that the greenhouse effect is robust in Venus. Due to its proximity to the sun, it receives more heat energy.

Still, it fails to radiate most of this energy back to space since the high carbon dioxide concentration in its atmosphere retains the heat energy.

The greenhouse effect on planet Venus makes it the hottest world, hotter than Mercury, closest to the sun.


Mercury planet is the smallest and closest to the sun. Due to its location within the solar system, it is only logical that anyone would think of it as the hottest planet.

However, Mercury has an almost non-existent atmosphere. The molecular components of the atmosphere enveloping Mercury do not exhibit the characteristics of greenhouse gases.

As a result, the exceptionally high heat energy that gets on the surface of Mercury from the sun is quickly radiated to space with almost no heat getting trapped within its atmosphere.

The Venusian atmosphere, which is mostly carbon dioxide, traps the heat that radiates back to space from the surface while allowing heat from the sun. This causes very high temperatures on the surface of the planet Venus.

The proximity factor could have easily made Mercury hotter than Venus, but the atmosphere and its contents have had a say in dictating the surface temperatures of these two planets.

In conclusion, Venus is hotter than Mercury because of the atmosphere’s role in retaining heat radiated back to space by the planetary bodies in the solar system.

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