It will come as no surprise that the solar system, shockingly, is very big! Spanning as much as one light year you’ll find a collection of all sorts of space oddities, from comets and asteroid belts. That’s not to mention the numerous planets and dwarf planets. However, what’s the closest planet to the Sun?
As you probably know, the Sun is located at the center of our solar system. In the past, it was thought that Earth was at the center of the universe, but we now know that to be incorrect.
The Sun is the source of all our light. It is over a hundred times our diameter and almost a million times bigger. The Sun is the center of our solar system. Without the Sun, life on Earth would have never existed. In fact, nearly all of the energy we use today originated in the Sun. The only exceptions are energy-derived nuclear fuel and geothermal schemes.
However, it is also an incredibly heavy ball of ‘burning’ gas, meaning tha objects that are closer than Earth are exposed to more radiation. Any close celestial bodies get exposed to heat. A lot of heat.
Thousands, if not hundreds of thousands, of comets and smaller objects, fall and burn up into the sun every year. However, other larger objects, like planets, can maintain their orbit while staying close to the sun. They do this by maintaining stable orbits.
So, which planet is the closest?
In this guide, we’re going to explain a little more about what the closest planet to the Sun. Of course, this planet is Mercury.
Which Planet Is Closest To The Sun?
So, as most people will likely already know, Mercury is the closest planet to the sun.
Being at a distance of only 36 million miles (57.9 million km), it is about half the distance as the next planet out. This planet is, of course, Venus. Venus orbits at around 67 million miles (108 million km) from the sun. Incidentally, despite it being farther from the Sun, Venus’s surface is hotter than Mercury due to its thick greenhouse gas atmosphere.
It’s certainly a lot closer than Earth, which sits at around 93 million miles (149.6 million km), almost 3 times the distance.
Of course, saying that Mercury is ‘close’ to the sun is purely on an astronomical scale. It’s still tens of millions of kilometers away from it!
Elliptical Orbit
However, that figure of 36 million miles (57.9 million km) is the average distance that Mercury is from the sun. Depending on when you catch it in its orbit, it can be much further or significantly closer to the sun.
That sounds a little weird, so let’s explain more about its elliptical orbit.
See, in many diagrams of the solar system, it’s very common to have the orbits of every planet be shown as completely circular, at their average distance from the sun.
It’s a very simple method of showing distances, and it more or less gets the point across on where they sit in the solar system.
However, the truth is that most planets’ orbits, or the orbits of any celestial body, are much less a perfect circle, and more of an ellipse, or oval shape. Or, as it is better known, an elliptical orbit.
The eccentricity, or how extreme this elliptical orbit is, varies from planet to planet. However, what this means is that in a planet’s orbit around the sun, there will be points when it is closer to the sun, and times when it is further away from it.
In Mercury’s case, this means that at its closest, it is only 46 million kilometers away, and at its furthest, it’s over 69 million kilometers away.
As we’ll soon find out, this also means that it can have some interesting results.
As an aside to this story Mercury’s orbit was one of the proofs for Einstein’s Theory of General Relativity. Before Einstein Mercury’s orbit was observed to precess in a way not explained in our earlier understanding of gravity. Precession is where the ecliptic orbit of a planet moves between orbits. Einstein’s theory explained the observations perfectly.
Mercury: Closest Planet To The Earth?
When you think of planets closest to the Earth, you’ll probably think of either Mars or Venus.
After all, when it comes to average distances from the sun, their averages are always on both sides of the earth. It’s like a celestial Goldilocks zone, in that way.
However, applying what we now know about elliptical orbits to these inner planets’ routes around the sun, you’ll find that, at various points of their orbits, these planets are much further apart from Earth than we might think.
And, because Mercury orbits the sun at a much faster speed than the other planets do, its elliptical orbit means that, at many times, it is much closer to Earth than either Venus or Mars is.
So, the next time someone asks you what the closest planet to Earth is (you know, whenever that happens to come up), you can say, with confidence and a little bit of a story behind it, that Mercury is the closest planet.
At least, sometimes.
Other Mercury Facts
So, aside from trivia around its distance, what else do we know about Mercury?
A Hot Planet (But Not The Hottest)
Being the closest planet to the sun, it’s no surprise that Mercury can get incredibly hot. At an average of a balmy 354 degrees Fahrenheit (179 Celsius), the surface of Mercury is hot enough to melt most metals, including tin!
However, despite how close it is, it can sometimes surprise people to learn that it’s not the hottest planet in the solar system. That honor goes to our twin planet, Venus.
Planet Venus, Objectively Hotter
Venus might be twice the distance from the sun as Mercury, but it has something that Mercury simply doesn’t: A thick atmosphere.
Venus has a very strong greenhouse effect (similar to the one on Earth, but much stronger) that traps any heat that might enter through the atmosphere from leaving, meaning that temperatures rise, and stay high, even when it is technically night.
Compare that to Mercury, which has no atmosphere and drops to -333 degrees Fahrenheit (-203 Celsius), and there’s no contest.
The result is a surface that, at 847 degrees Fahrenheit (453 Celsius) on average, can easily melt lead.
The Smallest Planet
Since Pluto was reclassified as a dwarf planet, Mercury has now become the smallest planet in the solar system.
With a radius of only 1,516 miles (2,440 km), it is almost half the radius of Earth and is only slightly larger than our moon!
Closing Thoughts
So, Mercury might be the closest planet to the sun, but its path around it is an interesting one!
Hi, my name is Jason Anderson, and I am a Physics Professor. Ever since I was a kid, I’ve been fascinated with space, the universe, the moon, you name it. I spent hours and hours at the planetarium close to my hometown, wondering what else could be out in the universe.
Since then, I’ve been an avid stargazer and astronomer, and love nothing more than spending my time charting stars, observing planets, and finding constellations.
This is why I decided to start Telescope Guru. I only wish to share this fun pastime with the world. With this site, I hope to answer all of your questions relating to astronomy, telescopes, and stargazing.
