Why Is Mercury Not The Hottest Planet? (The Reasons Why!?)

If you’re aware of the placement of each planet within our solar system I’m sure you’d be know that the closest planet to our Sun is in fact Mercury however, what may surprise you is that it isn’t the hottest planet within our solar system, the hottest planet is in fact Venus.

The main reasons why are because unlike Venus, Mercury doesn’t have an atmosphere therefore, it cannot trap heat from the Sun and it’s rate of reflectiveness is much lower than Venus too which makes it harder to maintain heat levels comparable to Earth’s so called sister planet. 

Of course I’ll go over the details more thoroughly throughout this article to help you understand in more detail why Mercury is not the hottest planet in our solar system.

How Hot Is Mercury?

At its hottest Mercury has been recorded to have achieved a maximum temperature of 427 degrees Celsius (801 Fahrenheit) whilst at its coldest it can achieve a bone shatteringly cold -180 Degrees Celsius (290 Fahrenheit).

Venus on the other has achieved a max temperature of 477 Degrees Celsius (891 Fahrenheit) with a low of around 460 degrees celsius (860 Fahrenheit) which simply means its blazing hot every minute of its extremely extremely long day (1 Day in venus is equal to 116.75 days in earth days).

On average Venus is over 30 Degrees Celsius (86 Fahrenheit) hotter than Mercury’s max temperature, which is pretty darn insane when you consider it’s 108 million km away from the Sun compared to Mercury’s 58 million km.

The Reasons Why Mercury Isn’t The Hottest Planet


There are 2 main reasons why Mercury is not the hottest planet within our solar system despite the it being much closer to the Sun than Venus ever is within its orbital cycle. The first reason is of course the lack of an atmosphere within Mercury and the second reason is due to the differences on both planets absorption and reflective rates.

Reason 1 – It Has No Atmosphere

The most obvious reason why Mercury isn’t the hottest planet in our solar system is due to its lack of an atmosphere. Venus on the other hand has an extremely thick atmosphere which means that not only is it an extremely reflective planet (I’ll explain why in the next reason) but, it’s also capable of trapping heat within its atmosphere allowing it to increase the surface temperature of the planet further.

Venus' thick atmosphere


In most cases when a planet is done absorbing as much light as it can, the light re-radiates back into outer space so, the lack of an atmosphere makes it pretty simple for Mercury

However, because Venus’ atmosphere is so thick (roughly 100 times that of earth) the re-radiation process is literally hundreds of times harder as more heat is trapped within. This is further amplified by the fact Venus’ atmosphere has huge amounts of infrared absorbing gases like Carbon dioxide which is shrouded in thick reflective clouds.

When all of these factors are taken into. account, it does make sense why Venus is generally hotter.

Reason 2 – It’s Absorption Rate Is Much Higher Than Venus

Due to the lack of an atmosphere, the heat and light that travels from the Sun to Mercury cannot actually be trapped on the planet and is instead absorbed. This is known as a planets albedo.

In short the albedo rating spans from 0 – 1 with 0 labeling an object as having the perfect rate of absorption and a rating of 1 meaning the object is a perfect reflector.

Mercury’s albedo rating is actually very similar to the moon at 0.0119 (with the Moons rating being 0.012). This means that for Mercury a little under 12% of the light that travels from the Sun to it is reflected and 88% of the heat is absorbed.

Venus on the other hand has an albedo rating of 0.9, which is in fact the highest rating within our solar. This is also one of the reasons why it’s the brightest planet within our solar system too.

Generally, most people would assume that Mercury is the hottest planet purely because it’s much closer to the sun than Venus, with Venus being roughly 2 times the distant away.

However, due to Venus’ extremely reflective nature and even taking into account the  amount of light and heat that reaches the planet being 4 times weaker (this is taking into account the distance squared train of thought regarding energy emissions), as Venus is essentially 9 times more reflective than Mercury along with its thick atmosphere, Venus at its peak and pretty much year round is a fair bit hotter than Mercury.


So they are the 2 reasons why Venus is the hottest planet in our solar system.

Hopefully this article has taught you something new today and if you feel it’s interesting enough to share , we would very much appreciate it if you did!

Thanks for reading.

2 thoughts on “Why Is Mercury Not The Hottest Planet? (The Reasons Why!?)”

  1. The article explains the phenomenon well. Would be nice if some of the repetitions were removed.
    Also, some Celsius and Fahrenheit conversions don’t appear to be correct – maybe in some instances you meant Kelvin and Rankine.


Leave a Comment