Concept

Mercury (planet)

Overview

Mercury is the first planet from the Sun and the smallest in the Solar System. It is a rocky planet with a trace atmosphere and a surface gravity slightly higher than that of Mars. The surface of Mercury is similar to Earth's Moon, being cratered, with an expansive rupes system generated from thrust faults, and bright ray systems, formed by ejecta. Its largest crater, Caloris Planitia, has a diameter of 1,550 km (960 mi), which is about one-third the diameter of the planet (4,880 km or 3,030 mi). Being the most inferior orbiting planet, it always appears close to the Sun in Earth's sky, as either a "morning star" or an "evening star". It is the planet with the highest delta-v required for travel from Earth, as well as to and from the other planets in the Solar System.

Mercury's sidereal year (88.0 Earth days) and sidereal day (58.65 Earth days) are in a 3:2 ratio, in a spin–orbit resonance. Consequently, one solar day (sunrise to sunrise) on Mercury lasts for around 176 Earth days, or twice Mercury's sidereal year. This means that one side of Mercury will remain in sunlight for one Mercurian year of 88 Earth days; while during the next orbit, that side will be in darkness all the time until the next sunrise after another 88 Earth days. Above the planet's surface is an extremely tenuous exosphere and a faint magnetic field just strong enough to deflect solar winds. Combined with its high orbital eccentricity, the planet's surface has widely varying sunlight intensity and temperature, with the equatorial regions ranging from −170 °C (−270 °F) at night to 420 °C (790 °F) during sunlight. Despite being the closest planet to the sun, it is the second hottest after Venus, lacking an atmosphere to trap heat. Due to its very small axial tilt, the planet's poles are permanently shadowed. This strongly suggests that water ice could be present in the craters.

Like the other planets in the Solar System, Mercury formed approximately 4.5 billion years ago. There are competing hypotheses about Mercury's origins and development, some of which incorporate collision with planetesimals and rock vaporization; as of the early 2020s, many broad details of Mercury's geological history are still under investigation or pending data from space probes. Its mantle is highly homogeneous, which suggests that Mercury had a magma ocean early in its history, like the Moon. According to current models, Mercury may have a solid silicate crust and mantle overlaying a solid outer core, a deeper liquid core layer, and a solid inner core. Mercury is expected to be destroyed, along with Venus, and possibly the Earth and the Moon, when the Sun becomes a red giant in approximately seven or eight billion years.

Mercury is a classical planet that has been observed and recognized throughout history as a planet (or wandering star). In English, it is named after the ancient Roman god Mercurius (Mercury), god of commerce and communication, and the messenger of the gods. The first successful flyby of Mercury was conducted by Mariner 10 in 1974, and it has since been visited and explored by the MESSENGER and BepiColombo orbiters.

Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).

In the original texts

Passages from public-domain books where Mercury (planet) is discussed.

By this means, as soon as any small portion of mercury is got beyond the end of the thread of glass, it breaks off, and falls into the ball in very small drops. This thread of glass is fastened by the heat given to the tube in making the bend next to the ball.
Various, Philosophical transactions, Vol. L. Part I. For the year 1757.
names the idea; states what it is; opens on it
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_Serpens_ is like Saturn and Mars. _Sagitta_ is like Saturn, and moderately like Venus. _Aquila_ is like Mars and Jupiter. _Delphinus_ is like Saturn and Mars. _Equus_ (or Pegasus). The bright stars are like Mars and Mercury. _Andromeda_ is like Venus. _Delta_ (or the Triangle) is like Mercury.
Ptolemy, Ptolemy's Tetrabiblos
names the idea; opens on it
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I will not dispute much whether they are different individuals or not. It is sufficient to know that this Mercury of whom Hermes speaks is, as well as Æsculapius, a god who once was a man, according to the testimony of this same Trismegistus, esteemed so great by his countrymen, and also the grandson of Mercury himself.
of Hippo Augustine, The City of God, Volume I
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'Tis a very sensible Question you ask, how the Air can affect the Barometer, when its Opening appears covered with Wood? If indeed it was so closely covered as to admit of no Communication of the outward Air to the Surface of the Mercury, the Change of Weight in the Air could not possibly affect it. But the least Crevice is sufficient for the Purpose; a Pinhole will do the Business. And if you could look behind the…
Benjamin Franklin, Benjamin Franklin
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At some points of its orbit it is nearer to the sun than at other points. The point where it is nearest to the sun is called its “perihelion.” Now it was found by observation that, from one occasion when Mercury is nearest to the sun until the next, Mercury does not go exactly once round the sun, but a little bit more. The discrepancy is very small; it amounts to an angle of forty-two seconds in a century.
Bertrand Russell, The A B C of Relativity
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Philosophers who discussed Mercury (planet)

Related ideas

Opposing perspectives

Ancient Greek astronomy

Place in the tradition

Part of Confirmation holism.

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