Earth Solar System

Planets in Order

Eight planets live within our solar system. Here's a quick overview of their order from the sun, and some of their features.

1. Mercury is the smallest planet in our solar system. It also has the shortest planetary year, taking just 88 days to orbit around the Sun.
2. Venus is the hottest planet in the solar system - with an average surface temperature of 465°C. The high temperatures and toxic sulfuric acid clouds make it impossible to support life.
3. Earth is the only planet in our solar system to have liquid water on its surface. Around two-thirds of the planet's surface is covered by oceans.
4. Mars gets its signature red colour from iron oxide dust.
5. Jupiter is by far the largest planet in the solar system. This gas giant is home to an estimated 79 moons.
6. Saturn is well known for its visible rings, made of ice and rock.
7. Uranus orbits on its side. Its clouds are made of a compound that smells like rotten eggs - hydrogen sulfide.
8. Neptune is furthest from the sun and the coldest planet. It is known for its supersonic strong winds.

If you are struggling to remember the order of the planets, try this mnemonic: My Very Excellent Mother Just Served Us Noodles!

Nearest Planet to Earth in Solar System

If you imagine the solar system from above, you may envisage the planets in a row. However, Mercury, Venus, and Earth rarely lie in a straight line from the sun as Mercury’s year is equal to 88 Earth’s days and Venus’s 225.

Most of the time, venus is the closest planet to Earth as it lies 67 million miles from the sun. The Earth lies 93 million miles from the sun. Every 584 days, Earth and Venus are 26 million miles apart. However, when they are on opposite sides of the sun, there is a massive 160 million miles between them and at this time only 33 million miles between Mercury and Earth.

Size and Mass of the Earth

Earth is not very big - it's only the fifth largest planet in the solar system. It is the largest of the inner, rocky planets (Mercury, Venus, Earth and Mars), but much smaller than the gas giants in the outer solar system.

Size: Earth has an equatorial radius of 6386 km (or 3963 miles).

Mass: Earth's mass is 5.972 x 10²⁴kg. This is equivalent to 5,972,000,000,000,000,000,000,000 kg!

Earth Orbiting the Sun

Like all planets in the Solar System, the Earth orbits around the Sun.

Years

Our planet is very far from the Sun - approximately 150 million kilometers - so during the 365 days of our year it makes a complete orbit. This is equivalent to a year on Earth.

Days

Whilst travelling around the Sun, the Earth constantly spins on its axis. It takes 24 hours to rotate - equivalent to a day on Earth. Some of these hours are spent facing away from the sun, resulting in what we call nights.

Seasons

The Earth's axis is tilted slightly to its orbital plane by 23.44°. As the Earth orbits the Sun, this results in greater heating and extended daylight hours in one hemisphere over the other. Essentially, this tilt is responsible for the cyclic changing seasons.

Fig. 2 - The northern and southern hemispheres experience opposite seasons at the same time

What Makes Earth Unique?

Earth is the only planet in the solar system that supports life. Why is this?

Liquid Water and The Goldilocks Zone

Liquid water is required by life as we know it. But what does this have to do with the three bears?

The Goldilocks Zone applies to the range of distances a planet can be from its host star to maintain liquid surface water.

• If a planet is too close to its star, surface temperatures will be too high, causing water to evaporate.
• If a planet is too far from its star, surface temperatures will be too low, causing water to freeze.

In our solar system, the Goldilocks Zone extends from the orbit of Venus to the orbit of Mars.

• Venus is too hot.
• Mars is too cold.
• Earth is just right!

Temperatures on Earth allow vast oceans of liquid water, allowing life to thrive.

Plate Tectonics

Another unique feature of Earth is its plate tectonic system.

Many scientists believe that without water, Earth's tectonic movements would not be possible. Water lubricates the plates, which leads to the variation between continents and seafloors. Additionally, plate tectonics help to regulate Earth's temperature, so liquid water can be maintained.

Interactions with Other Objects

The conditions supporting life on Earth are regulated by other objects in our solar system.

The Moon

Our large moon stabilises our planet's rotation. This helps to prevent drastic movements of the poles that would cause major changes in the planet's climate. The moon also creates tides, which shape surface conditions.

Jupiter

Despite its great distance from Earth, Jupiter has a major effect on Earth. Its huge mass acts as a vacuum for debris that clutters the solar system, preventing it from colliding with the Earth.

I hope that this has explained the importance of Earth's position in the solar system to you. Remember that liquid water is essential for life. The Earth's distance from the sun maintains liquid water on its surface.

^{1. Britannica, Earth, 2021}

^{2. Clara Moskowitz, What makes Earth unique?, 2021}

^{3. Daisy Dobrijevic, Solar system planets, order and formation: A guide, 2022}

^{4. Mary Whitehorne, Why Earth is Closest to Sun in Dead of Winter, 2007}

^{5. NASA, Earth, 2022}

^{6. NASA, Our Solar System, 2022}

^{7. NASA, The Milky Way Galaxy, 2015}

^{8. National Geographic, Goldilocks Principle, 2022}

^{9. Ulrich Kutschera, Evolution, Brenner's Encyclopedia of Genetics, 2013}