What Planet Is Closest to the Sun?

When asking the question: What planet is closest to the sun? we can’t forget about the smallest of the planets: Mercury! Besides being the tiniest planet in the Solar System, Mercury has the quickest orbit around the Sun. Like its namesake, the swift-footed ancient Roman god, Mercury speeds around the Sun in a mere 88 Earth days, compared to Earth’s 365 days and faraway Neptune’s 60,190 Earth day orbit (165 Earth years!)

What is the Order of the Nine Planets?

Mercury, Venus, Earth, and Mars make up the Solar System’s inner four rocky planets, while distant Jupiter, Saturn, Uranus, and Neptune are gas giants. The dwarf planet Pluto resides beyond Neptune.

Here is our Solar System’s planet placement order, starting from the Sun and moving outward.

Order from Sun	Planet Name
1	Mercury
2	Venus
3	Earth
4	Mars
5	Jupiter
6	Saturn
7	Uranus
8	Neptune

There are several ways to remember the order of planets closest to the Sun and moving outward. Mnemonics use the first letter of each planet’s name in an easy-to-remember phrase.

My Very Excellent Mother Just Served Us Nachos (or Noodles)

As you can see, the M in “my” stands for Mercury. Then V in “very” for Venus, and so on.

Planets in Order of Size

Comprehending the sheer size of space takes mental gymnastics. Our solar system resides within the Milky Way Galaxy on one of the outer Orion spiral arms. When you consider how many galaxies astronomers explore, it brings the vastness of space into a clearer view.

Mercury is our solar system’s smallest planet, slightly larger than Earth’s moon. Similar to Earth’s moon, it has no atmosphere, so debris-impact craters litter Mercury’s pockmarked surface.

In order of size by radius, here is the planet line-up.

Planet Name	Radius Miles	Radius km	Mass (kg)
Jupiter	43,441	69,911	1.9 X 10^27
Saturn	36,184	58,232	5.7 X 10^26
Uranus	15,759	25,362	10.2 X 10^25
Neptune	15,299	24,622	8.7 X 10^25
Earth	3,959	6,371	5.97 X 10^24
Venus	3,761	6,052	4.9 X 10^24
Mars	2,460	3,390	6.4 X 10^23
Mercury	1,516	2,440	3.3 X 10^23

Jupiter, Saturn, Uranus, and Neptune. Credit Lunar and Planetary Institute

The planets line up differently in order of size by mass, with Neptune and Uranus trading places.

Look at the mass of Jupiter in the chart above. 1.9 X 10^27 kg. What does that mean? The short answer is that it means Jupiter is gigantic! The longer answer is that Jupiter has a mass of 318 Earths. That’s big!

Mercury, the planet closest to the Sun, comes in last place as the smallest planet by radius and by mass.

Mercury, Venus, Earth, and Mars. Credit: Lunar and Planetary Institute

How Many Moons Does the Planet Closest to the Sun Have?

When thinking about what planet is closest to the Sun, also consider the number of moons and natural satellites that planet has. It raises the question, how many moons does Mercury have? The answer is ZERO! Mercury has no moons of its own.

Mercury’s lack of natural satellites stems from its very proximity to the Sun. If a large object drew close enough to Mercury to become its satellite, the Sun would snatch it up into its own vast gravity field.

Mercury’s small size and hill sphere combine with its weak gravity and contribute to its isolated orbit. Now add Mercury’s nearness to the Sun’s immense gravitational pull to better understand the planet’s inability to attract and hold a moon.

The planet closest to the Sun also has no cosmic dust and gas rings surrounding it.

what planet is closest to the sun — Image Credit: SpacePlace NASA

Why Doesn’t Mercury Burn Up Since It’s So Close To The Sun?

Since Mercury is sun-scorched, why doesn’t it just burn up? Its surface temperatures vary from extremely hot to icy cold.

Mercury’s dayside superheats to around 800 degrees Fahrenheit (430°C). But at night, it plummets hundreds of degrees below freezing, down to -290°F (-180°C). It’s so cold that ice may form in some surface craters.

While the Sun superheats one side of Mercury, it is still not hot enough to melt the dense planet. The radius of its metallic inner core is 1,289 miles (2,074 kilometers). So that’s almost 85% of the planet’s entire radius.

Evidence exists that part of the inner core is molten or liquid. It is similar to the Earth’s solid inner core, surrounded by a fluid, molten iron, and nickel outer core. Mercury’s outer shell is like Earth’s rocky mantle and crust.

How Big Would the Sun Look if You Could Stand on Mercury?

Standing on Mercury, the Sun looks three times larger in the skies than it appears on Earth. The Sun is the same size, but you’re closer to it. The sunlight is seven times brighter and hotter than it is on Earth.

Mercury has an elliptical orbit with a slow rotation, making the Sun seem to rise, set, and rise again. When it sets in the evening, the same phenomenon takes place. The slow rotation makes one Mercury solar day (one complete day-night cycle) equal 176 Earth days. That’s the same as just over two Mercury years.

The orbit gets Mercury within 29 million miles (47 million kilometers) of the Sun. Then sweeps it as far away as 43 million miles (70 million kilometers).

Characteristics of the Planet Closest to the Sun

This tiny planet, Mercury, has exciting characteristics.

How Old is Mercury?

Mercury formed about 4.5 billion years ago. Gravity pulled nearby dust and gasses together to create the planet closest to the Sun.

What is Mercury Made Of?

Even though it has a tiny radius and mass, Mercury is very dense. It is second only to Earth’s density and has a big metallic core.

The core’s 1,289 miles (2,074 kilometers) radius comprises about 85 percent of the entire planet’s radius. That means the planet’s outer shell is only about 250 miles (400 kilometers) thick.