Mercury is the closest planet to the Sun at an average distance of about 77 million kilometers. Mercury was named after the Roman god of travel, merchants, commerce, and the god of wealth. The planet’s astronomical symbol (☿) also reflects this.

Mercury is also the smallest planet in the Solar System and has the highest density of all the planets. Mercury’s mass is about 2.3 times that of Earth, whereas its volume is only 0.07 times that of Earth – making it one of the densest planets in our system.

Mercury’s orbit around the Sun is the most eccentric of all the planets, meaning that its distance from the Sun varies more than any other planet’s. Because it’s so close to the Sun, Mercury is only visible in the early morning and evening skies during specific times throughout the year, depending on where you are on Earth or which hemisphere you’re viewing it from. 

The young planet’s surface is similar to the Moon and has been heavily cratered from impacts. The surface is also covered in smooth plains and large scarps that formed when the planet contracted early in its history. Like Venus, Mercury has a very thick atmosphere consisting of helium and sodium gas. You may have heard of the “twilight zone” of Mercury, which is a band in the planet’s atmosphere where temperatures drop to -193°C.

While Earth orbits the sun for 365 days, Mercury orbits the sun for 88 days. In other words, it has a “year” that lasts less than an Earth year – which means it rotates on its axis in a similar time frame as well!

Mercury is mainly composed of rock and metal, just like Earth, but its core may still be molten. Scientists believe this because the planet still has a magnetic field which is thought to be caused by a molten core.

Although scientists think Mercury may have once supported life, current evidence suggests that it could not. In 2006, NASA’s MESSENGER probe was put in orbit around the planet, and its discoveries have helped scientists better understand this mysterious planet.