The Planet Mercury


The Planet Mercury is the closest planet to our sun and is the smallest planet in the solar system. It is named after a roman god.

The Planet Mercury PhotoIt has no natural satellites and no substantial atmosphere.

Facts about Planet Mercury

Diameter: 4,878km (3,032 miles)
Surface Temperature: Ranges from -170 degrees at night to 350 degrees in the day.
Orbit: 57,910,000 km (0.38 AU) from Sun. Orbiting the Sun once every 88 days.
Average Distance: About 58 million km (36 million miles)
Time to Rotate: 58.6 days
Mass: 3.30e23 kg (5.5% of Earth’s)
Moons: 0
Period of Rotation: 58.6462 days.


Mercury has a very elliptical (oval-shaped) orbit. At perihelion (at its closest point) it is about 46 million km (28.58 million miles) from the Sun, but at aphelion (at its farthest point) it is 70 million km. Mercury is about 77.3 million km (48 million miles) from Earth at its closest approach. Mercury is not easily seen from Earth due to its small angular separation from the Sun. Mercury moves around the sun faster than any other planet. Mercury travels about 48 km (30 miles) per second and it takes 88 Earth days to orbit the sun. The Earth goes around the sun once every 365 days (one year).


The planet rotates once about every 59 Earth days, a rotation slower than that of any other planet except Venus. Due to the planet’s slow rotation on its axis and rapid movement around the sun, a day on Mercury lasts 176 Earth days (interval between one sunrise and the next).


Mercury is the second densest major body in the solar system after Planet Earth and its density is slightly less than the Earths. Mercury’s smaller mass makes its force of gravity only about a third as strong as that of the Earth. An object that weighs 100 pounds (45.4 kg) on the Earth would weigh only about 38 pounds (17.2 kg) on Mercury.

Mercury has a large iron core which is most likely at least partially molten and generates a magnetic field about 1% as strong as that of Earth’s. Mercury’s interior appears to resemble that of the Earth. Both planets have a rocky layer called a mantle beneath their crust and both planets have an iron core.


Mercury is only 4,878km (3,030 miles) across. It is about the size of mainland USA and roughly one-third Earth’s size. Earth’s diameter is 12,742 km (7917.5 miles). It is also not much larger than our moon which is 3475 km (2,160 miles) wide. It is smaller than Jupiter’s Ganymede moon and Saturn’s Titan moon, which are the first and second most largest moons in the solar system.


The surface of Mercury consists of smooth plains, cratered terrain and many deep craters similar to those on the moon. The craters formed when small comets or meteors crashed into the planet. Caloris Basin is the largest crater on the surface of Mercury. It has a diameter of 1300 km (800 miles).

Like the other terrestrial planets (Venus, Earth and Mars) Mercury is made mostly of rock and metal. Mercury’s surface appears to be much like that of the moon. It reflects approximately 6 percent of the sunlight it receives, about the same as the moon’s surface reflects. Like the moon, Mercury is covered by a thin layer of minerals called silicates in the form of tiny particles.


Scans of Mercury made by Earth-based radar indicate that craters at Mercury’s poles contain water ice. The floors of the craters are permanently shielded from sunlight, so the temperature never gets high enough to melt the ice.


Mercury is a planet of extreme temperature variations. It is hotter on Venus, but with less fluctuations. The temperature on the planet may reach 450 degrees C (840 degrees F) during the day. But at night, the temperature may drop as low as -170 degrees C (-275 degrees F). The sunlight on Mercury’s surface is 6.5 times as intense as it is on Earth due its closeness to the sun.


Mercury is dry, extremely hot and almost airless. Planet Mercury is too small for its gravity to retain any significant atmosphere over long periods of time. The weak atmosphere contains hydrogen, helium, oxygen, sodium, calcium and potassium.

Due to the heat of the planet, the very thin atmosphere is blasted off its surface by the solar wind and quickly escapes into space. Mercury’s atmosphere is constantly being replenished.

Mercury does not have enough atmosphere to slow down meteoroids and burn them up by friction. The sun’s rays are approximately seven times as strong on Mercury as they are on the Earth. The sun also appears about 2 1/2 times as large in Mercury’s sky as in the Earth’s.


The Greeks gave it two names: Apollo for when it appeared as a morning star and Hermes when it came as an evening star.

In Roman mythology Mercury is the god of commerce, travel and thievery, the Roman counterpart of the Greek god Hermes, the messenger of the Gods. The planet probably received this name because it moves so quickly across the sky


The plant and animal life of the Earth could not live on Mercury because of the lack of oxygen and the intense heat. Scientists doubt that the planet has any form of life.


Because of Mercury’s size and nearness to the sun, the planet is often hard to see from the Earth without a telescope. At certain times of the year, Mercury can be seen low in the western sky just after sunset. At other times, it can be seen low in the eastern sky just before sunrise.


When viewed through a telescope, Mercury can be seen going through ‘changes’ in shape and size. These apparent changes are called phases and resemble those of the moon. They result from different parts of Mercury’s sunlit side being visible from the Earth at different times.


Mercury has been known since ancient times. Until the mid-1960’s, astronomers believed that Mercury rotated once every 88 Earth days, the same time the planet takes to go around the sun. If Mercury did this, one side of the planet would always face the sun and the other side would always be dark. However, radar studies conducted in 1965 showed that the planet rotates once in about 59 days.

The only spacecraft to come close to Mercury was Mariner 10 from 1974 to 1975, which was only able to map 40%–45% of the planet’s surface.



Mariner 10: Planet Mercury was explored in three flybys by the Mariner 10 spacecraft in 1974 and 1975.

Messenger Spacecraft: NASA’s second mission to Mercury is named MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging). It was launched on 3 August, 2004 from the Cape Canaveral Air Force Station on a Boeing Delta 2 rocket.

In 2004, the United States launched the Messenger probe to Mercury. Messenger flew by Mercury twice in 2008 and once in 2009. The probe entered orbit around the planet in March 2011. Messenger was the first spacecraft to orbit Mercury. It mapped Mercury’s surface and studied its composition, interior structure and magnetic field.

In the future, Russia is planning to explore Mercury with the Mercury-P Spacecraft and Europe/Japan with BepiColombo Spacecraft.

BepiColombo is a joint mission by European Space Agency and Japan. It will orbit Mercury with two probes: one to map the planet and the other to study its magnetosphere. It is named after Giuseppe (Bepi) Colombo an Italian scientist. Probes will be launched on a Russian Soyuz rockets in 2018. The spacecraft will make close approaches to other planets en route to Mercury. The spacecraft will reach Mercury in about 2025.


Mercury has been suggested as one possible target for space colonization of the inner solar system, along with Mars, Venus, the Moon and the asteroid belt. Permanent colonies would almost certainly be restricted to the polar regions due to the extreme daytime temperatures elsewhere on the planet, although excursions to the other parts of the planet would be feasible with appropriate measures

More Facts on Planet Mercury – Did you know?

Mercury is the fastest moving planet in our Solar System and is the nearest planet to the Sun. Mercury is one of the four terrestrial planets, being a rocky body like the Earth. It is the smallest of the four. The largest feature on Mercury is the Caloris Basin.

How big is the planet mercury? 2440 km
When was planet mercury discovered? Unknown
Color of planet mercury? Orangery
How long is a year on Mercury? 88 days. Venus is 225 days, Mars is 687 days and Earth is 365 days.

Mercury orbits the sun at an average distance of about 36 million miles (58 million kilometres), compared with about 93 million miles (150 million kilometres) for Earth.


Planet Mercury (True Books) by Ann O Squire (Author)

The Planet Mercury Links



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