# Mercury

*all about the planet mercury*

By [The Mercury](https://paragraph.com/@mercury) · 2023-09-25

planet, mercury, earth, mercury retrograde, moon, space

---

**_Smallest planet_**

Mercury is the smallest planet in the solar system. It is 18 times lighter than Earth, and its diameter is barely two-fifths the size of Earth. To better understand the size of Mercury, compare it to the Moon - Mercury is only a third larger than our natural satellite.

The already small planet became even smaller over time. The planet's core has cooled, causing Mercury's radius to decrease by about 5-10 kilometers

**_one day on Mercury_**

A solar day—the amount of time it takes the Sun to rise, set, and rise again in the same place—on Mercury lasts approximately 176 Earth days. And here’s another unusual fact: one year on this planet lasts only 88 Earth days, that is, almost two times shorter than one Mercury day. Why is this happening?

The smallest planet rotates slowly around its axis - one revolution takes 59 Earth days (one sidereal day). However, sunrises and sunsets on this planet are significantly different from those on Earth. Due to the planet's elongated orbit, the Sun rises (and sets) twice on Mercury. Thus, the Sun takes longer to reappear in the same place, and one solar day lasts twice as long as one year.

Despite the fact that Mercury rotates slowly around its axis, it rapidly rushes along its orbit around the Sun - at a speed of 47 km/s. For comparison, the second fastest planet in the solar system, Venus, moves at a speed of 35 km/s.

**_What is Mercury made of?_**

Since Mercury is a terrestrial planet, it is mainly composed of iron, nickel and silicates. Most of Mercury's volume—about 61%—is occupied by a huge iron core, roughly the size of our Moon. For comparison, the Earth's core makes up only 16% of its volume. The planet's core is surrounded by a mantle approximately 400 kilometers thick. The surface of Mercury also resembles the moon - it is rocky, hard and densely covered with craters.

Craters appear from collisions with asteroids or other space objects; The more craters there are on a planet, the older it is. The presence of so many craters on Mercury indicates its advanced age.

**_What is Mercury retrograde?_**

Mercury is called retrograde when it begins to move in the “reverse” direction for observers on Earth. In fact, the planet does not change the direction of its movement, it is just an optical illusion. You can learn more about retrograde movement in one of our previous articles.

The small, fast planet moves in the “reverse” direction three or four times a year for three weeks. In 2023, Mercury's retrograde motion will be observed from April 21 to May 14, from August 23 to September 15, and from December 13 to January 1, 2024.

---

*Originally published on [The Mercury](https://paragraph.com/@mercury/mercury)*