Fun Facts About Mercury: What Mercury Is Like and Its One-of-a-Kind Characteristics
Mercury is the smallest planet and it's packed with extremes: 88-day years, 176-day solar days, wild temperature swings, and even a comet-like tail. In this guide, you’ll find the most interesting Mercury facts (size, color, temperature, composition, moons) plus quick, practical tips for spotting Mercury in the sky. Since it stays close to the Sun, timing is everything – open the free Star Walk app to track Mercury’s position in seconds and catch it during the best viewing windows.
Contents
- Mercury facts in short
- What’s Mercury like? Size, temperature, composition
- What does Mercury look like?
- Mercury in the sky 2026: visibility guide
- Mercury F.A.Q.
- Most interesting facts about Mercury: to sum up
Mercury facts in short
- Planet type: terrestrial
- Radius: 2440 km (1516 miles)
- Mass: 3.3011×10^23 kg
- Aphelion: 69.8 million km (43.4 million miles)
- Perihelion: 46.0 million km (28.6 million miles)
- Average distance from the Earth: 77 million km (48 million miles)
- Surface temperature: -173°C to 427°C (−280 °F to 800 °F)
- Solar day length: 176 Earth days
- Sidereal day length: 59 Earth days
- Year length: 88 Earth days
- Age: 4.503 billion years
- Named after: Roman god of commerce
7 fun facts about Mercury we bet you didn’t know
Mercury doesn't have seasons like Earth
On Earth, the seasons occur because our planet is tilted, approximately 23.5 degrees relative to the ecliptic. In contrast, Mercury's axis is nearly straight, tilted only about 0.034°, meaning neither hemisphere can tilt more toward the Sun. To understand how it works, take a look at the article “What Causes the Seasons to Change?”.
However, Mercury still experiences a type of seasonal change: thermal seasons. Its orbit is highly elliptical, so it is sometimes much closer to the Sun and at other times much farther away. When Mercury reaches aphelion (its farthest point), it receives less sunlight and cools down. At perihelion (its closest point), Mercury receives much more sunlight and heats up. Mercury's distance from the Sun at its aphelion is approximately 1.5 times greater than its perihelion distance, which is why the difference is so noticeable.
Mercury has a tail
Many people know comets have tails. But have you heard about a planet that has one? Mercury has a cometlike tail produced when solar radiation and the solar wind release sodium atoms from the planet’s surface. It’s not easy to see: you’ll have to take a long-exposure photo using a telescope and a special filter.
Mercury is not the hottest planet
Mercury is the closest planet to the Sun, but it isn’t the hottest. The title goes to Venus. Here’s why: Mercury has only an extremely thin exosphere, so it can’t trap heat – the planet’s surface bakes in sunlight, then cools down fast at night. Venus, on the other hand, is wrapped in a thick carbon-dioxide atmosphere that creates an intense greenhouse effect, keeping the planet scorching hot day and night.
A day on Mercury lasts two Mercury years
Mercury spins once every about 59 Earth days, but one solar day – from sunrise to sunrise – takes about 176 Earth days. That’s roughly two Mercury years, since Mercury orbits the Sun in only about 88 Earth days. In other words, on Mercury, you could celebrate two birthdays before sunset.
Mercury can have two sunrises in a row
Around perihelion, when Mercury is closest to the Sun, the planet moves fastest along its orbit. For a short time, this orbital motion can overtake its slow rotation. That's why from certain locations on its surface, the Sun may appear to slow down, stop, or even move backward across the sky. This phenomenon can create the illusion of double sunrises. The Sun rises, reverses, sets again, then rises once more.
Mercury is a Budha planet
In Sanskrit, Mercury is called Budha (not to be confused with Buddha, the founder of Buddhism). The Vedic texts call it Budha planet, and refer to it as a deity, the son of Soma (or Chandra, the Moon god) and Tara (wife of Bṛhaspati, the god of Jupiter).
Mercury is the smallest – and it’s getting even smaller
Mercury is the smallest planet in the Solar System, and it’s still shrinking. As the planet’s interior slowly cools, Mercury contracts, and its crust crumples like a drying apple. That process creates huge cliff-like “wrinkles” called lobate scarps – long ridges and steep slopes that cut across craters and plains, showing that Mercury has remained geologically active far longer than you might expect.
What’s Mercury like? Size, temperature, composition
How big is Mercury?
Mercury is the smallest planet in the Solar System in both mass and diameter. It’s 18 times less massive than the Earth, and its diameter barely reaches two-fifths of the Earth’s size. To give you a better understanding of Mercury’s size, let’s say that it’s only a third larger than the Moon.
Surprisingly enough, this small planet got even smaller over time. Cooling of its core has caused the entire planet to shrink, reducing Mercury’s radius by about 1-7 kilometers.
How hot is Mercury?
The temperature of Mercury’s surface varies more than on any other planet in our Solar System. It can range from −173 °C (−280 °F) at night to 427 °C (800 °F) during the day. This happens because the smallest planet has almost no atmosphere to trap heat, and it quickly loses the energy it receives from the Sun during the day.
Although Mercury is the closest planet to the Sun, it isn’t the hottest one (Venus is).
Do you know which object is the coldest, the biggest, or the fastest in the Solar System? Which planet hosts the highest mountain, and where is the largest ocean of liquid water (spoiler: not on the Earth)? Take this quiz and learn more about the space record holders!
How long is a day on Mercury?
A solar day – the amount of time it takes the Sun to rise, set, and rise to the same place again – on Mercury lasts about 176 Earth days. And here is another weird fact about Mercury: a solar day on this planet is about twice as long as a year, which lasts 88 Earth days. How come?
The smallest planet spins slowly about its axis – one rotation takes 59 Earth days. However, its sunrises and sunsets are quite different from those on Earth. Due to the planet’s unusual 3:2 rotation pattern (it rotates three times on its axis for every two orbits around the Sun) and its eccentric orbit, the Sun can appear to rise twice: once, shortly before setting, and then again from some parts of the surface. The same thing occurs in reverse at sunset. Thus, it takes much longer for the Sun to appear in the same place again, and one solar day lasts almost twice as long as a year.
Even though it spins slowly, Mercury travels around the Sun faster than any other planet – at 47 km/s (29 mi/s). In comparison, the second-fastest planet in our Solar System, Venus, has a speed of 35 km/s (21 mi/s).
What is Mercury made of?
Since Mercury is a terrestrial planet, it’s mainly composed of iron, nickel, and silicate rock. It has a large iron core, which is about 60% of the planet’s volume (in comparison, the Earth’s core is only 16%), and a 400-kilometer (250 miles) thick outer shell. By the way, Mercury’s core is about the same size as our Moon. Another similarity to the Moon is that the planet’s dry, rocky surface is full of craters.
Craters are the result of impacts with asteroids or other space objects – the density of craters on a surface generally indicates its age. Since Mercury’s surface is heavily cratered, it’s most likely ancient.
What does Mercury look like?
In space, Mercury looks roughly similar to the Moon, a little grayer and bigger than our natural satellite. In NASA images of Mercury, you can see bright impact craters with “rays” of pulverized rock spreading outward. Mercury’s surface is also shaped by long ridges, fractures, and jagged cliff-like scarps — features that, along with countless craters, create the planet’s rugged landscape. With only an extremely thin exosphere to soften the sunlight, shadows are razor-sharp, and the landscape has a stark, high-contrast look.
In the sky, to the naked eye, Mercury looks like a bright “star” low above the horizon, often tinted yellow or orange by Earth’s atmosphere. In binoculars, it remains star-like. In a small telescope, you can see Mercury’s phases (like the Moon’s): it changes from a thin crescent to a half phase and a gibbous shape as it moves around the Sun. The best views come during twilight, when Mercury is highest above the horizon, and the sky is still relatively dark.
Mercury in the sky 2026: visibility guide
Here is a quick visibility guide for Mercury in the upcoming months of 2026:
- March: Mercury becomes unobservable as it reaches inferior conjunction on March 7. Later in the month, it appears in the morning sky. On March 19, Mercury ends retrograde motion.
- April: Mercury is a morning object, reaching its greatest elongation on April 3. This is the year’s greatest elongation of Mercury!
- May: The morning apparition ends in early May as Mercury disappears into the sunrise glow; it reaches its superior conjunction on May 14.
- June: Mercury appears in the evening sky, reaching its greatest elongation on June 15, best visible from the Southern Hemisphere. The planet begins retrograde motion on June 29.
- July: Mercury heads toward inferior conjunction on July 13, appearing lower in the evening sky; it switches from retrograde back to direct motion on July 23 and becomes a morning object by the end of the month.
- August: Mercury is visible in the morning sky, best-seen from the Northern Hemisphere. It reaches its greatest elongation on August 2.
- September: Mercury remains in the morning sky into mid-September; it reaches superior conjunction on September 27, getting lost in the Sun’s glare.
- October: Mercury returns to the sky as an evening object. On October 24, Mercury begins retrograde motion.
- November: Mercury reaches inferior conjunction on November 4 and disappears into the Sun’s glare. The planet ends retrograde motion on November 13, and reaches its greatest elongation on November 21, appearing in the morning sky.
- December: Mercury remains a morning object until mid-December, gradually slipping back into the sunrise glow.
Mercury events to see in 2026
Mercury likes to stay close to the Sun, so you can’t see it whenever you want, but when it does pop into view, it often comes with some great sky moments: close passes with the Moon, planets, or stars. To quickly check whether Mercury is visible now from your location (and exactly where to look), use the Star Walk 2 planetary guide. Just type the name of a planet in the search field, and the app will show you its position in the sky.
March 7: Mercury at inferior solar conjunction
On March 7, 2026, Mercury reaches an inferior solar conjunction, passing between Earth and the Sun and disappearing into the Sun’s glare. After its recent appearance in the western evening sky, the planet shifts into the morning sky, heading toward greatest elongation on April 3.
March 14: Mercury near Mars
- Conjunction time: 06:44 GMT
- Conjunction distance: 3°58′
- Close approach time: March 15, 19:09 GMT
- Close approach distance: 3°21′
On March 14, Mercury and Mars will appear close together in the morning sky, low above the eastern horizon shortly before sunrise. Mercury will shine at magnitude 2.5, while Mars will be brighter at magnitude 1.1. The conjunction will be more favorable for observers in the Southern Hemisphere, where Mars rises earlier and appears higher above the horizon. In the Northern Hemisphere, Mars rises almost at the same time as the Sun, making it harder to spot.
March 17: Moon near Mercury
- Conjunction time: 14:07 GMT
- Conjunction distance: 1°59′
- Close approach time: 15:45 GMT
- Close approach distance: 1°45′
On March 17, the 2%-illuminated Moon will be close to Mercury (mag 1.6) in the sky. They will be positioned in the constellation Aquarius. Due to their proximity to the Sun, both objects will be difficult to see. In the Northern Hemisphere, the Moon and Mercury will be close to the horizon. In the Southern Hemisphere, Mercury will appear higher above the horizon during morning twilight, providing a better view.
March 19: Mercury ends retrograde motion
Mercury has been moving retrograde since February 25 and will change back to direct motion on March 19. This means the planet will stop drifting "backward" against the background of the stars and will begin moving eastward (prograde) again. If you are still concerned about Mercury retrograde, read our article on retrograde motion in astronomy to finally understand how it works.
April 3: Mercury at greatest western elongation (best of 2026 ⭐)
On April 3, at 22:32 GMT, Mercury (mag 0.3) will be at 27°49′ west of the Sun. The planet will be visible in the constellation Aquarius before sunrise. This is the year’s greatest elongation of Mercury, so don’t miss your chance to see this elusive planet! This will also be the best morning apparition of Mercury for the Southern Hemisphere in 2026.
Two more planets, Mars (mag 1.2) and Saturn (mag 0.9), will rise near Mercury. These planets are usually bright enough to be observed without optics, but this time they will be very close to the rising Sun, lost in its glare.
Mercury F.A.Q.
What color is Mercury?
Mercury is primarily dark gray. A planet’s color depends on the color of its surface and its reflective abilities. Unfortunately, Mercury’s rocky exterior, covered with dust, doesn’t give a wide variety of colors.
How many moons does Mercury have?
Mercury doesn’t have any moons. Because it orbits so close to the Sun, the Sun’s strong gravity would pull away or destabilize any potential moon, preventing Mercury from keeping one for long.
How far is Mercury from the Sun?
Its average distance from the Sun is about 58 million km (36 million miles). Thus, among other planets in the Solar System, Mercury is the closest one to the star.
When was Mercury discovered?
Mercury has been observed since ancient times. The earliest recorded observation occurred in 265 BCE. The first people who observed Mercury through a telescope were Galileo Galilei and Thomas Harriot in the 17th century.
Why is Venus hotter than Mercury?
Despite Mercury being the closest planet to the Sun, Venus is hotter because of the thick Venusian atmosphere trapping heat. Mercury, in its turn, has no significant atmosphere and can’t hold the Sun’s energy.
What does the Sun look like from Mercury?
If you could stand on Mercury, at aphelion (the farthest Mercury can get from the Sun), you would see the Sun twice as big as it appears from the Earth. At perihelion (the closest distance), the Sun would appear three times as large as it does on our planet.
Most interesting facts about Mercury: to sum up
Mercury is full of surprises. It’s the closest planet to the Sun, yet not the hottest. It’s small, yet it has a giant iron core the size of the Moon. Mercury has no moons and almost no atmosphere. It is also difficult to observe because it stays close to the Sun and near the horizon. But we've made it easier for you – use the free Star Walk 2 app to find Mercury in seconds from your exact location.
You can also watch the fun and educational cartoon about Mercury that explains the main facts about the planet in simple words.
Wishing you clear skies and happy observations!
