Eli5: Venus is the second planet from The Sun, Mercury is first. Why is Venus still the hotttest planet in the Solar System?
In: Planetary Science
Mercury has no atmosphere. Venus has a very thick atmosphere made up of gasses that hold heat very well.
Mercury may be sitting a little closer to the campfire, but Venus is wrapped up in a super thick sleeping bag.
It’s mostly due to a powerful greenhouse effect on Venus. Mercury essentially has no atmosphere while Venus has a thick atmosphere made mostly of carbon dioxide. This thick atmosphere traps heat that the surface radiates. This also means that Venus is hot all around on both the day side and the night side.
On the other hand, there is nothing to stop Mercury from radiating its heat out into space. While the day side is very hot, the night side is actually very cold because the surface cools off fairly quickly once it is no longer getting heat from the sun.
All things being equal, Mercury ought to be hotter. But all things aren’t equal.
The main difference is that Venus has a dense atmosphere (much denser than Earth’s) made mostly of carbon dioxide. You’ve probably heard of the greenhouse effect in relation to global warming on Earth; well on Venus it’s that much worse.
Mercury on the other hand has almost no atmosphere to speak of. At any given time, the side facing the sun is extremely hot while the side facing away is extremely cold. It gets a lot of energy from the sun, perhaps more than Venus, but it has no way to hold onto that heat so on average it’s not as hot.
So basically Mercury is like being naked in the desert, but Venus is like wearing a snowsuit in a slightly cooler desert.
Greenhouse Gases. Kinda in the same way global warming works on earth where gas lets heat in but diminishes the ability for it to be transferred out
Mercury doesn’t have much of an atmosphere compared to Venus’ super dense atmosphere.
The atmosphere holds onto heat like a blanket. So Venus’s “blanket” holds onto the heat from the sun, while the heat from the sun on Mercury just escapes into space.
Imagine it’s super duper cold out and two people are sitting around a campfire. One is right next to the fire but is just wearing a tshirt and shorts. The other person is a bit further away from the fire but wrapped in lots of nice warm blankets. The person further away with the blankets will be warmer. Fire is the sun, and the two people are Mercury and Venus. (It’s not a perfect analogy because in this instance the people are also producing their own body heat which planets don’t do. But gives a good visual.)
On a hot day being outside might be hot. But if you go into a black car it’s sweltering.
That’s how it is with Mercury and Venus. Mercury may be closer to the sun but it has no/very little atmosphere so it doesn’t trap the heat in/ this creates a polarity on Mercury where the side facing the sun is very hot due to being directly exposed but the other side cold due to not trapping any heat.
Venus has a very thick atmosphere, so although it’s farther it’s trapping in the heat very much like the car in the analogy above.
You know how earth’s average temperature is rising due to greenhouse effect caused by CO2 emissions? Venus’ atmosphere is almost exclusively made out of CO2 and other gases that cause greenhouse effects. Venus is a planetary-scale greenhouse so it gets really really hot.
Venus has a greenhouse gas atmosphere, so it’s like being in a greenhouse. Mercury has no atmosphere so it’s like being in no house
Not for nothing but couldn’t this particular question be answered through a Google search?
Although I do admit that the first answer about the camp fire is clever.
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