in ,

Mercury – The Smallest Planet of Solar System

Mercury Quiz
Mercury Quiz

Mercury, the smallest planet, goes whizzing around the Sun at a dazzling 31 miles per second. The planet travels so fast that it makes a complete loop in only 88 days. People have known about Mercury for thousands of years. It is named for the Roman god, Mercury, the fastest of all the gods.

Mercury Facts For Kids

  • Mercury is the closest planet to the Sun.
  • It’s the smallest planet in our solar system.
  • It doesn’t have any moons.
  • Mercury has a very thin atmosphere.
  • A day on Mercury is longer than its year.
  • The planet has many craters and mountains.
  • It’s named after the Roman messenger god.
  • Temperatures can be very hot and very cold.
  • Mercury has no liquid water on its surface.
  • It can be seen from Earth without a telescope.

Solar System

Mercury, the smallest and innermost planet in our solar system, is located closest to the sun, and orbits around it faster than any other planet, taking a mere 88 earth days – a characteristic that led to its naming after the swift Roman god. Despite its proximity to the sun, Mercury experiences extreme temperature fluctuations due to the lack of an atmosphere to retain heat.

Its unique surface, scarred with craters similar to our moon, is a testament to its numerous encounters with meteors and comets. However, due to its closeness to the sun’s intense brightness, Mercury remains invisible to the naked eye from Earth, necessitating the use of a telescope for observation.


Mercury and Venus, the two closest planets to the sun in our solar system, share intriguing similarities and stark differences. Both devoid of moons and incapable of supporting human life due to their inhospitable atmospheres, they nonetheless exhibit contrasting geological features; Mercury’s surface is heavily pockmarked with craters, much like our moon, whereas Venus’s terrain is marked by volcanic activity.

Visibility from Earth is another area of contrast; both planets can be observed without a telescope, but Mercury’s nearness to the sun often makes it harder to spot, unlike Venus, which is the brightest planet in our night sky. Regarding temperature, Mercury experiences intense fluctuations, soaring up to 800 degrees Fahrenheit in daytime but plummeting drastically at night. Venus, however, remains consistently scorching due to its dense atmosphere.

Smallest planet

Mercury, the smallest planet in our solar system, approximately 3,032 miles in diameter and only slightly larger than Earth’s moon, intrigues children as a point of study. Its fascinating surface, heavily cratered like our moon, along with its proximity to the sun, yet lack of the highest temperatures due to its almost non-existent atmosphere, make it an intriguing celestial body.

Despite its small size, Mercury’s unique characteristics and position in our solar system emphasize its significance, embodying the notion that even the smallest entities in our universe can spark substantial interest and hold considerable importance.


In our solar system, Mercury, due to its proximity to the Sun, holds the record for both extreme temperatures and the shortest planetary year. This close neighbor to the Sun can endure daytime temperatures reaching a searing 800 degrees Fahrenheit (430 degrees Celsius), outdoing even the hottest oven.

Yet, it can counter this with a dramatic nighttime drop to -290 degrees Fahrenheit (-180 degrees Celsius), due to its lack of an atmospheric heat trap, making it colder than Earth’s lowest recorded temperature. Despite its nearness to the Sun and extreme temperature fluctuations, it is Venus, not Mercury, that holds the title for the hottest planet, courtesy of its dense atmosphere.

Another notable characteristic of Mercury is its speedy orbit around the Sun; it has the shortest year among all planets, completing a full orbit in merely 88 Earth days.

Mariner 10

The American robotic space probe, Mariner 10, made history as the first spacecraft to visit Mercury, the smallest planet in our solar system. The mission, which took place from 1973 to 1975, yielded a treasure trove of intriguing information, captivating not only scientists but also sparking the curiosity of children.

On its groundbreaking journey, Mariner 10 made three close approaches to Mercury, taking the first close-up images of the planet. These images unveiled surprising characteristics of Mercury, such as its large iron core and magnetic field, despite its relatively small size.

The spacecraft’s findings also included the revelation that Mercury’s surface is heavily cratered, bearing a strong resemblance to our moon. The valuable insights gathered from the Mariner 10 mission have significantly enriched our comprehension of this enigmatic planet located so close to the sun.

Mercury’s surface

Mercury presents a captivating landscape that’s particularly fascinating to young adventurers. Resembling our moon, it’s marked by an abundance of craters and mountains, a testament to the countless meteor impacts it has endured.

The surface of this intriguing celestial body is composed of a grey, rocky substance and is peppered with distinctive deep, wide depressions known as ‘hollows.’ Its proximity to the sun causes Mercury’s surface temperature to soar to a blistering 800 degrees Fahrenheit during the day.

However, in the absence of an atmosphere to retain this heat, temperatures plummet to minus 290 degrees Fahrenheit at night, making Mercury a planet of extreme contrasts.

Messenger probe

Launched by NASA, the Messenger probe has revolutionized our understanding of Mercury, the closest planet to the Sun, by delivering fascinating information to science enthusiasts, especially kids. In March 2011, Messenger made history as the first spacecraft to orbit Mercury, making ground-breaking discoveries that included the presence of water ice in the planet’s permanently shadowed craters – an unexpected revelation for scientists.

The probe further revealed that Mercury’s surface is riddled with impact craters, a result of frequent collisions with other space objects. Essentially, the Messenger probe’s mission has greatly enriched our comprehension of this small, incandescent planet.

No moons

Mercury, an intriguing planet within our solar system, is distinctive because it does not possess any moons, unlike our own Earth which has one, and several other planets that have multiple. This absence of moons is attributed to Mercury’s close proximity to the sun, the immense gravitational pull of which prevents any moon from maintaining a stable orbit around the planet.

Therefore, when we admire our own moon in the nightly sky, we should recognize the unique privilege it is, as not all planets are fortunate enough to have one.

Shortest solar day

Mercury, our solar system’s smallest planet, holds a captivating fact about its solar day that would intrigue kids. Contrary to what one might assume due to its close proximity to the Sun, a day on Mercury, measured from sunrise to sunrise, isn’t swift but is the shortest solar day among all planets.

This is attributed to Mercury’s slow rotation speed, requiring approximately 59 Earth days to complete a full spin on its axis. However, this slow rotation, combined with its fast orbit around the Sun, results in a solar day – the duration from one sunrise to the next – being only 176 Earth days. Interestingly, even though a year on Mercury, dictated by its full orbit around the Sun, is merely 88 Earth days, a day on Mercury is paradoxically twice as long!

Mercury’s orbit

Situated closest to the sun in our solar system, Mercury’s intriguing orbit promises to capture the curiosity of children. Its proximity to the sun enables it to orbit faster than any other planet, completing a full revolution in a mere 88 Earth days, thus marking the shortest year in our solar system.

But Mercury’s orbit is not a perfect circle as we see with most planets; instead, it adopts an elliptical or oval shape, leading to variations in its distance from the sun. Despite its swift orbit, Mercury has an exceptionally slow rotational speed, with a single day, defined as one full rotation on its axis, lasting a staggering 59 Earth days.

Mercury Image - Science for Kids All About Mercury
All about Mercury, the smallest planet. This planet  is the densest planet next to Earth.

Mercury is the densest planet next to Earth. It has a solid core and crust. Its core is made of metal – mostly iron. Its crust is made of rock. Because Mercury is so small, it has a very weak magnetic field. Gases, like oxygen or hydrogen, blow away into outer space. Mercury doesn’t have a blanket of gases to protect it like Earth. Instead, it has a very thin atmosphere. When comets and meteors enter the Earth’s thick atmosphere, they usually burn up long before they reach Earth. When comets and meteors enter Mercury’s atmosphere, they don’t slow down. Instead, they slam into the planet, causing craters and pock marks.

Mercury, the Fastest Roman God Image
Mercury planet is named for the Roman god, Mercury, the fastest of all the gods.

Fun Facts about Mercury for Kids

  • Mercury has extreme temperatures because it is so close to the Sun and because it has almost no atmosphere. The sunny portion of the planet has a temperature of 800 degrees. The other side of the planet is -300 degrees. Ouch!
  • Mercury can be seen from Earth. Look for it just as the Sun rises in the morning or as the Sun is setting at night. It looks like a bright star that sits close to the Sun.
  • Mercury is just a bit larger than our moon.
  • Some of the craters on Mercury are very deep. Scientists believe there is frozen ice in deep craters at the poles.
  • One crater is over 8 miles long.
  • If you weigh 60 pounds on Earth, you’d weigh only 18 pounds on Mercury.
Mercury's Core Layers Image
All About Mercury: It has a solid core and crust. Its core is made of metal – mostly iron. Its crust is made of rock.

Mercury Vocabulary

  1. Whiz: fly or flash past
  2. Dense: heavy, solid
  3. Magnetic field: force that causes gravity
  4. Crater: deep, round hole

Learn More All About Mercury, the Smallest Planet of Solar System

Take a peek at this Mercury video:

A video documentary all about Mercury.

Mercury Q&A

Question: Does Mercury have volcanoes on it?

Answer: Mercury’s crust is too hard and thick for volcanoes to form. There are no tectonic plates that move like there are on Earth. Scientists believe Mercury might have a molten, or liquid metal, crust, but the molten liquid can’t erupt through the surface.