Why is Venus hotter than Mercury?

Generally, the further that you go away from the Sun, the colder each planet gets. This is the case for most of the planets, but there’s one big exception to that; Venus. Even though Venus is further away from the Sun than the planet Mercury, it’s actually hotter than the smaller planet. But why is this, and what causes Venus to be hotter than Mercury? Well, that’s what we’re going to run through quickly.

The reason why Venus is hotter than Mercury is because it has a thick atmosphere primarily made up of carbon dioxide, which is a greenhouse gas that helps retain the heat from the Sun. In comparison to this, Mercury has almost no atmosphere, so any heat that beats down on the planet isn’t retained.

How hot can the planet get? Well, on average Venus has been shown to stay at a temperature of around 460°c. Mercury, in comparison, stays at a temperature of 430°c on average across the course of time. Not too much distance, but when you consider Mercury is tens of millions of miles closer to the Sun, it can be difficult to know why.

The atmosphere of Venus is made up of 96% carbon dioxide, and 3.5% nitrogen, along with trace amounts of other gases like carbon monoxide too. And actually, at the outer atmosphere of Venus, the temperature isn’t actually that hot, which is why there have been many different flyby missions to Venus. You can check out some more interesting facts about Venus by clicking this link.

The atmosphere of Venus is surrounded with yellow sulfuric clouds, and the atmosphere itself is very thick; about 100x the thickness of our atmosphere here on Earth. Venus was once thought to be a potential location that astronomers could visit, with hot but capable temperatures – the many space missions throughout the 1960s and 1970s discovered the true temperature of its surface and put these possibilities to bed.

So when the sunlight passes through the Venusian atmosphere onto the surface of the planet, it doesn’t bounce off the planet and escape like it does on planets with little atmosphere. Instead, the heat becomes trapped, causing high temperatures on the planet’s surface than can be in excess of 500°c. We call this the greenhouse effect, as it’s the same principle that we use in greenhouses here on Earth.

Mercury, in comparison to Venus and most other planets in the solar system, has very little atmosphere – in fact, many folks refer to Mercury as having no atmosphere at all. This isn’t strictly true, as the planet does has some form of thin atmosphere surrounding it.

The truth is that instead of a traditional atmosphere that we have on Earth, Mercury is left with a thin exosphere that is made up of oxygen, sodium, hydrogen, helium and other trace gases too. However, missions to Mercury have left astronomers in doubt as to how much oxygen is actually in the exosphere there (it was previously thought that up to 42% of the atmosphere was oxygen).

Now, did Mercury have an atmosphere once upon a time? There’s definitely a distinct possibility that it did. Astronomers believe that billions of years ago Mars had an atmosphere that was gradually worn down by solar winds, so it’s possible that the same could be said for Mercury too.

This thin exosphere means that the temperature on the planet Mercury can vary drastically, from over 400°c at one point to as cold as -180°c on the dark side of the planet. So, it’s clear to see why Mercury’s lack of atmosphere has left it as the second hottest planet as opposed to being the first. The surface temperature of the planet is still extremely hot, mind you.

To sum it up, it’s pretty easy to see why Venus has the title of the hottest planet in the solar system, despite actually being further away from the Sun than the much smaller Mercury. There are those that think that Venus may have been habitable once upon a time, with much research around the topic in recent years. Of course, this would have been potentially billions of years ago, and now, Venus would be