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Mercury facts: First rock from the sun -

Mercury orbits the Sun at an average distance of about 57.9 million kilometers (36 million miles). It's the innermost planet in our solar system, i.e. the planet closest to the sun.

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It's the smallest planet -

Mercury's diameter is approx. 4,880 kilometers (3,032 miles), making it the smallest planet. Mercury is bigger than Pluto, but it's still considered the smallest planet because of Pluto's designation as a dwarf planet.

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Dramatic temperatures -

Wild temperature variations are the norm on Mercury, where surface temperatures can range from -173°C (-280°F) at night to 427°C (800°F) during the day.

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It has a short year... -

One year on Mercury, in which it completes one full orbit around the Sun, passes fast. It takes just 88 Earth-equivalent days.

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...But a long day -

However, in contrast, a single day on Mercury—where it completes one full rotation on its axis—is equivalent to 59 Earth-equivalent days.

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No atmosphere -

Mercury has a very thin exosphere composed mostly of oxygen, sodium, hydrogen, helium, and potassium. The heat on Mercury means the atoms escape quickly into space, with many blasted off its surface by the solar wind.

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A rough surface -

The lack of atmosphere means the planet doesn't have much to protect it from outside forces. As a result, Mercury's surface is covered with craters, ridges, and terrains that resemble the Moon's.

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Caloris Basin -

The biggest of these is the Caloris Basin. One of the largest impact craters in the solar system, it measures about 1,550 kilometers (960 miles) in diameter.

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Caloris Basin -

It's speculated to have been produced by the same remnant planetary building blocks (planetesimals), asteroids, and comets that also struck the moon around 3.9 billion years ago. During this time, an especially intense period of bombardment took place in the inner solar system.

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No moons -

One big difference between Mercury and many other planets in our solar system? It has no natural satellites or ring systems.

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It has a high density -

Mercury is the second densest planet in the solar system, due to its large iron core, which makes up about 85% of its radius.

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Weak magnetic field -

Mercury has a weak magnetic field that's only about 1% as strong as Earth's. The field is thought to be generated by its partially molten core.

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Axial tilt -

Even though Mercury is so close to the sun, due to the planet's axial tilt, the polar regions of Mercury receive very little direct sunlight.

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Icy poles? -

Despite its proximity to the Sun, radar observations suggest there are water ice deposits in permanently shadowed craters at Mercury's poles.

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NASA's MESSENGER -

The MESSENGER spacecraft, launched by NASA from Cape Canaveral, Florida, on August 3, 2004, fundamentally changed our understanding of Mercury.

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NASA's MESSENGER -

NASA's MESSENGER spacecraft orbited Mercury from 2011 to 2015, providing detailed information about its surface and composition.

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"Discovery" of Mercury -

As one of the five planets visible from Earth, no one person is credited with the "discovery" of Mercury. When Galileo used his first telescope, which confirmed the Sun-centered solar system theories of Copernicus, it wasn't powerful enough to reveal Mercury's disk shape.

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The first telescope -

However, Thomas Harriott and Galileo Galilei are among the first recorded people to observe Mercury, with the newly invented telescope, in 1603.

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Pierre Gassendi -

In 1631, Pierre Gassendi, a French mathematician and philosopher, used a telescope capable of watching Mercury as it crossed the face of the Sun.

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Mercury's symbolism: Sumeria -

To the ancient Sumerians, the planet we know today as Mercury was personified by the god Nabu. He was the patron god of the art of writing, scribes, literacy, and wisdom.

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Roman mythology -

Mercury is named after the Roman god Mercury, the messenger of the gods, symbolizing commerce, communication, and travel.

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Greek mythology -

Mercury is equivalent to Hermes in Greek mythology. Hermes is the god of trade, eloquence, and thievery, who is known for his cunning and speed.

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Egyptian mythology -

In Egyptian mythology, Mercury is connected to Thoth, the god of writing, wisdom, and magic, often depicted with an ibis head.

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Alchemy -

In alchemy, Mercury (or quicksilver) represents the principle of fluidity and transformation, due to the dual nature of the element as both solid and liquid.

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Wednesday's planet -

Wednesday is associated with Mercury in many cultures and languages. This is reflected in names like "Mercredi" in French and "Miércoles" in Spanish.

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Astrology -

In Western astrology, Mercury rules over the zodiac signs Gemini and Virgo, governing communication, intellect, and reasoning.

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Mercury retrograde -

For several weeks each year, Mercury seems to have a retrograde motion, appearing to move backward in the sky due to its placement inside Earth's orbit. In astrology, Mercury retrograde periods are believed to cause disruptions in communication, travel, and technology.

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Tarot -

The planet Mercury is associated with the Magician card in the Tarot, which symbolizes intelligence, communication, and skillful use of resources.

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Mercury symbol -

The alchemical and planetary symbol for Mercury is ☿. It depicts a caduceus (a staff intertwined with two serpents) surmounted by the god Mercury/Hermes.

Sources: (NASA) (Space.com) (Cool Cosmos) (European Space Agency) (Planetary Society) (Astrology and Mythology)

See also: 9/11 as seen from space and other out of this world photographs

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