Planet Mercury in color

Mercury is the innermost planet in the Solar System. The Romans named it after the fleet-footed messenger of the gods, as it seemed to move more speedily than any other planet.

Mercury is Dense

Mercury is the second smallest planet in the solar system and is only larger than Pluto, which is technically not a planet anymore anyway. Mercury is the second densest planet after Earth, having a large iron core with a radius of 1,100 to 1,200 miles – roughly about 75% of the planet’s radius. Mercury’s outer shell, comparable to Earth’s outer shell (or mantle), is only 300 to 400 miles thick. Its magnetic field is considered to be a small version of Earth’s; however scientists are uncertain of the strength of the field.#1

Temperature Extremes

There is lot of difference in the day and night temperatures. Day time temperatures on Mercury’s surface can reach 801 degrees Fahrenheit and nighttime temperatures on the surface can drop to -279 degrees Fahrenheit. This is due of the fact that the planet has no atmosphere to retain that heat.

Atmosphere on Mercury

Mercury has almost no atmosphere; it is too small and has inadequate gravity to hold onto an atmosphere. Mercury has a thin exosphere which is made up of atoms blasted off its surface through solar wind and striking micrometeoroids. Owing to the planet’s extreme surface temperature, the atoms quickly get away into space. Unlike other planetary atmospheres, no wind erosion of the surface happens and meteorites do not burn up because of friction.

Best time to observe Mercury


Because Mercury lies so close to the Sun, it is usually lost in the glare of the star. It is not easy to directly observe Mercury from Earth except during twilight. Mercury is often called a morning star because it shines brightly just before the sun rises in early morning hours. It has also been called an evening star as it is often visible for a brief period of time just after the Sun sets. With the exception of for solar eclipse Mercury can be viewed from Earth’s Northern Hemisphere only. Although it’s extreme elongations take place in Declinations south of the celestial equator, such that one can see it at favorable apparitions from moderate latitudes in the Southern Hemisphere in a fully dark sky. Observers from the Earth can watch Mercury pass across the face of the sun and this event is called a transit. These rare transits fall within May 8 and November 10.#2

Time on Mercury

Scientists used to believe that the same side of Mercury always faces the sun, however in 1965 astronomers discovered that it rotates three times during every two orbits. Owing to its close location to the Sun, Mercury has become tidally locked to the Sun, or nearly so. The consequence is that Mercury rotates very slowly. The length of one day on Mercury (sidereal rotation) is equal to 58.646 Earth days. However even as Mercury’s days are very long, its revolution around the Sun is fairly fast. Mercury can complete one orbit around the Sun in just 88 Earth days, which is equal to about 3 months here on Earth.

Your weight on Mercury

Did you know that you will weigh lesser on Mercury than your weight on Earth? Not for the reason that you would lose weight on the spaceship, however it is because of the fact that Mercury is smaller and has lesser gravity. If you weight is 70 pounds on Earth, you would weigh roughly about 27 pounds on Mercury.

Mercury Has Wrinkles

Mercury surface

Researcher in recent times found some evidence that Mercury has a molten core, as it has not cooled completely. As Mercury’s iron core cooled it contracted, or shrunk, therefore Mercury has wrinkles. Because of this its rocky crust became wrinkled which are named as wrinkles Lobate Scarps by scientists. These scarps can be hundreds of miles long and even up to a mile high.

Planet Mercury’s surface is covered with craters. Asteroids and comets that hit plant’s surface over the time have produced these craters. All celestial bodies in the Solar System are subject to these bombardments and many of the planets have the ability to heal through natural geological processes.

One of the main features on Mercury’s surface is the Caloris Basin which is about 1300 km in diameter. It is considered to be similar to the large basins (maria) on the Moon. Similar to the lunar basins, it was possibly caused by a very large collision early in the history of the solar system. In addition to the heavily cratered topography, Mercury also has regions of comparatively smooth plains. Some may be the due to ancient volcanic activity however some may be because of the deposition of ejecta from cratering impacts.

Missions to Mercury

Two spacecrafts (Mariner 10 and MESSENGER) have visited Mercury. Marriner 10 flew by three times in 1974 and 1975. Merely 45% of the surface was mapped (however, it is too close to the Sun to be safely imaged by HST). MESSENGER was launched by NASA in 2004 and will orbit Mercury starting in 2011 after a number of flybys. Its first flyby in Jan 2008 presented new high quality images of some of the terrain not seen by Marriner 10.

Related Mercury Articles
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