Why doesn't Mars have an atmosphere?

The atmosphere of a planet can vary a lot, and it can make a massive difference to the weather on the planet. Take Venus for example; it’s the hottest planet in the solar system solely because it has a very thick atmosphere that retains all of the that it receives from the Sun. Mercury, in comparison, has barely any atmosphere at all, and even though it’s much closer to the Sun than Venus, is actually a lower temperature on average on the planet.

And if we go a little further out from those two we come to Earth, which has an atmosphere that allows humans to survive. But what about Mars, which is commonly referred to as having no atmosphere or lacking an atmosphere? Well, we’re going to take a quick look at that now.

The fact of the matter is that it’s not that Mars has literally no atmosphere; it just has very little of an atmosphere in comparison to most other planets, including Earth.

However, it is true that Mars barely has an atmosphere, and for a long time astronomers wondered why that was the case. In more recent years, we’ve discovered that Mars likely had a magnetic field that protected the planet, which was lost billions of years ago.

So there’s definitely the potential that Mars had an atmosphere just like Earth at some point in time, and billions of years ago, it may have had water running across its surface and even life on the planet too.

But with the disappearance on the magnetic field around the planet meant that the planet was subject to strong solar winds, which eventually over time, caused the Martian atmosphere. So the answer is that Mars likely did have a thick atmosphere once upon a time, but it has slowly eroded away as it was subject to solar winds. You can check here for more facts about Mars, but for now, let’s compare the Martian atmosphere to other planets.

And actually, one of the major factors of how hot a planet will stay over the course of time is whether it has enough greenhouse gases in its composition. This is probably best exemplified by looking at the three planets Venus, Earth and Mars.

First, we’ll start with Mars, which as said above, has lost most of its atmosphere. even though it’s made up of a whole lot of carbon dioxide, in comparison to Earth this is actually very little. So, it doesn’t have enough of an atmosphere to retain the heat, and it’s nowhere near thick enough to do so either.

Next we have Earth, which is sort of a balance between the two. You may think; but I thought the Earth’s atmosphere was primarily nitrogen and oxygen? And yes, whilst this is true, there are still relatively large amount of trace greenhouse gases in the atmosphere too. This amount is a lot more than Mars, and it’s what creates a habitable environment for humans.

So, we can live on Earth because of this extra percentage of greenhouse gases which keeps us warm. The other extreme is Venus, which has a super thick atmosphere that is mainly made up of carbon dioxide. This thick atmosphere retains a lot of the heat that comes from the Sun, meaning that the planet has an extremely high temperature that can reach as high as 460°c.

This gives us a good comparison about the lack of atmosphere on Mars and why it has such a big impact on the temperature of the planet, as well as the weather there too.

Mars isn’t alone in lacking what many astronomers consider to be a true atmosphere – Mercury also has very little of one, and it results in a lower average temperature on the planet. Like the other planets though, it’s thought that Mars has an internal heating system too, with a hot inner core that helps to contribute to the temperatures of the planet. Though despite this, it’s still much colder than Earth.