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Why isn’t Mercury the Hottest Planet?

If any planet in our Solar System were going to be the hottest, you would have to think it would be Mercury.


It is the closest to the sun, and its name is synonymous with temperature because of the metal of the same name which used to be in thermometers. However, this is not the case.

In this article, you’ll find some quick facts about Mercury, as well as an explanation as to why it isn’t the hottest planet.

We will also reveal which planet is the hottest planet, and why!


The Planet Mercury: Quick Facts

Here are some quick and interesting facts concerning Mercury.

Mercury is the closest planet to the sun.

As such, it takes the least amount of time to orbit the sun of any of the planets in the Solar System. One year on Mercury is only 88 days on Earth.

sun and planets

While a year on Mercury passes by pretty quickly about Earth, a day on Mercury is a different story. It takes the planet 176 Earth days to rotate once on its axis.

Due to its speedy orbit, it was named by the Romans after their god Mercury, who was the swiftest of all the gods.

Mercury is the smallest of all the planets and only has about 38 % the gravity of Earth. That means that if you weigh 200 pounds on Earth, you’d only be 56 pounds on Mercury!

So why isn’t Mercury the hottest planet?

Though it would seem to make sense that Mercury is the hottest of all of the planets in our Solar System, this is simply not the case.


Since Mercury lacks an atmosphere, it has no way of trapping the heat that is generated by the sun, thus leading it to have periods of both hot and cold.

Though it isn’t the hottest planet, it is still comes in a respectable second place, even without an atmosphere.


How Hot is Mercury?

The surface temperature of Mercury is believed to be about 800 degrees Fahrenheit or around 430 degrees celsius.

What is the hottest planet?

The hottest planet in the Solar System is none other than the second planet from the sun, Venus.

Venus is the second planet from the Sun and is also the closest planet to our little blue home, Earth. 

It is one of the four inner rocky planets, and astronomers often refer to it as Earth’s twin because of the similarities in their size and density. 

nasa image venus
This picture of Venus was captured by the Mariner 10 spacecraft during its approach to the planet in early 1974. Courtesy: Nasa

Venus also has crushing air pressure, which is more than 90 times the atmospheric pressure of earth. That would be akin to being a mile deep in an ocean on Earth

Why is Venus Hotter than Mercury?

While it is further away from the sun than Mercury, it has a dense atmosphere that traps the heat from the sun.

This raises the overall sustained temperature on its surface above the levels found on Mercury.


How Hot is Venus?

The surface temperature has been observed to be close to 900 degrees Fahrenheit or 475 degrees Celsius which is hot enough to melt some metals. 

This raises the overall sustained temperature on its surface above the levels found on Mercury.

The Surface of Venus is covered in mountains and volcanoes which scientists believe to be active.

venus surface volcano

And there it is! Mercury might be the closest to the sun and also the fastest planet, but Venus is the hottest.

Planets & Science

planets grouped together

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