Which Is the Hottest Planet in Our Solar System?
Last Updated: September 20, 2021
Though Earth is the only planet we’ve been able to physically visit so far (aside from robotic exploration), scientists have developed methods of measuring, estimating, and understanding our neighboring planets. They’ve even discovered which is the hottest planet in this arm of the Milky Way galaxy.
Venus is the hottest planet in our solar system, able to regularly reach surface temperatures higher than 465 degrees Celsius or 869 degrees Fahrenheit. Despite Mercury’s proximity to the sun, its atmospheric composition and cloud layers trap heat more efficiently than Mercury.
Here’s what you need to know about Venus and its scorching surface, as well as the advantage it has over its closest competitor for the hottest planet in the solar system.
How scientists measure extra-planetary temperature
Before delving into the specifics of the temperatures on other planets, it’s worth addressing how we know those temperatures at all. This simple answer is that it’s the work of decades of estimation and data collection.
As mentioned, scientists from institutes such as NASA have been exploring our solar system with robotic measurement devices since the 1950s, when the first satellites were launched.
The former Soviet Union had a space program called “Venera” whose goal was to gather more information about Venus by sending multiple space probes. Between 1961 and 1984, 10 of these space probes landed on the Venusian surface. However, since Venus is extremely hot, none of these robots lasted more than two hours.
Since then, they’ve constructed more advanced, multifunctional, and accurate instruments that can measure light and heat energy from great distances. Most temperature measurements for other planets are conducted by infrared probes sent as close to the planet’s surface as possible while remaining recoverable.
Those measurements are combined with the planet’s distance from the sun, its atmospheric composition and how we know those materials to interact with heat, and the size of the planet itself.
All of this information is put into various formulas to create a reasonably accurate summary of the temperature range on a particular planet’s surface. The validity of these formulas has been confirmed and improved by data from the Mars rovers’ temperature-gauging equipment.
Average Temperature on Each Planet
- Venus: 880°F (471°C)
- Mercury: 800°F (430°C)
- Earth: 61°F (16°C)
- Mars: -20°F (-28°C)
- Jupiter: -162°F (-108°C)
- Saturn: -218°F (-138°C)
- Uranus: -320°F (-195°C)
- Neptune: -331°F (-201°C)
- Pluto: -388°F (-233°C)
NASA's various probes are equipped with state of the art technology. They can make various measurements from orbit, including surface temperatures.
How Venus traps heat
Venus, the second planet from the sun, was the first planet to be explored by a spacecraft. Venus is lit up in phases similar to the moon that can be seen from Earth with an ordinary telescope, so it’s been studied planet-side since ancient times.
Its atmosphere is dense and composed of just the right materials to induce massive heat retention. Venus is hot due to the same greenhouse effect as modern emissions are creating on Earth.
The Mariner 2, launched by NASA in the 1960s, conducted a 42-minute scan of the planet’s atmosphere before continuing to orbit. Since then, many other agencies and spacecraft have explored the planet and recorded it.
Venus has intense coloration and odd rotation that has earned it a reputation as something of a dark mirror of Earth. Scientists have even given it the nickname of our “sister planet” or “toxic twin.”
Though new research has revealed the potential for microbial life high in the outermost cloud layers, it’s unlikely that Venus could sustain Earth-like life. It is similar to Earth in many ways. It is very similar in size – roughly 38,000 kilometers in circumference to Earth’s 40,000 kilometers, making it about 1.1 times smaller.
It has a rocky, solid surface composed of multiple (potentially active) volcanoes and asteroid impact craters running along massive plateaus and mountain ranges obscured by cloud cover.
Venus’s toxic atmosphere
Venus is beautiful and would be the most logical choice for exploration if it weren’t for that atmosphere. The gaseous layer surrounding Venus is incredibly dense, more than 90 times denser than Earth’s atmosphere, and is composed primarily of carbon dioxide and sulfuric acid clouds. This makes it extraordinarily toxic.
This pressure and composition mean that the gasses are creating an intense “greenhouse effect” on the surface. The thick atmosphere traps heat from the sun more quickly and easily than anywhere else in the solar system, meaning the planet can reach temperatures upwards of 465 degrees Celsius—hot enough to melt lead.
Because Venus also has incredibly long days and relatively short nights (its “day” is about 243 days on Earth and longer than its 225-Earth-day year), the surface is exposed to the sun more often than it is not.
This, combined with the incredible heat retention of the atmosphere, means that the nights on Venus are as hot as the days are.
An artist rendition of what the surface might look like on planet Venus.
Why Mercury isn’t the hottest planet in our solar system
You might be thinking to yourself “Hold on! Isn’t Mercury really close to the Sun? Why would Venus be hotter than Mercury??”
well, Mercury is indeed the closest planet to the sun, and though it hasn’t been as widely explored as Venus, we still know quite a bit about it from the measurements we have taken over the years.
Mercury receives the most direct and intense solar radiation because of its proximity. The sun-facing side of the planet can and regularly does reach up to about 426 degrees Celsius, or 800 degrees Fahrenheit. So, on its sun-facing side, it is nearly as hot as Venus.
The main reason Mercury isn’t the hottest planet in our solar system despite its proximity to the sun is its atmosphere or lack thereof. Like Venus and Earth, Mercury has a gaseous layer surrounding it. Unlike either twin planet, though, this layer is incredibly thin.
Scientists refer to it as an exosphere, given that it only covers the outermost layer of the planet, far from the surface. It’s composed primarily of oxygen, sodium, hydrogen, helium, and potassium. It’s incredibly thin and therefore makes a poor conductor of heat.
So, the side of the planet not immediately facing the sun actually gets incredibly cold… down to minus 180 degrees Celsius or minus 290 degrees Fahrenheit.
And that’s why Venus is hotter than Mercury!
By using the most reliable information we have, scientists have confirmed that, though Venus is more similar to Earth in measurement than any other planet in our solar system, it is nowhere near as habitable.
Venus is the hottest planet in our solar system for many reasons, including the composition of its atmosphere and the planet’s rotation speed. It might have been an habitable world millions of years ago but unfortunately, it is located too far away from the goldilock zone and sadly this turned the planet into a hellish world overtime.
Written by Lizzie B.
I have always had a deep fascination with the stars, but particularly asteroids. I enjoy the idea of philosophizing with the planets, personifying them and their traits to build stories & studying their changes. You can see more about how I value the planets, stars and asteroids (specifically) at backyardbanshee.com
Is the order of the planets important? In a way, yes, for the stability of our solar system is entirely based on where each planet is currently located.
Almost all major planets have moons and scientists are discovering new ones every year. Let’s visit some of these beautiful worlds.