Mercury Facts
planet mercury
Image taken by the NASA probe Messenger on its approach to Mercury.
Planet Mercury Facts
  • Mercury is the planet nearest the sun. It has a diameter of only 3,032 miles (4,879 km), around 40% of Earth's diameter.
  • The planet orbits the sun at an average distance of around 36 million miles (58 million km), compared with 93 million miles (150 million kilometers) for Earth.
  • Mercury is the smallest planet in the solar system, Jupiter's moon Ganymede and Saturn's moon Titan are also both larger in diameter.
  • Mercury orbits the sun faster than any other planet, taking only 88 days to make one complete orbit.
  • The planet rotates on its axis extremely slowly, taking 59 days compared to Earth's 24 hours.
  • The sun appears around two and a half times larger in its sky compared to how we see the sun on Earth.
  • Despite incredibly warm surface temperatures water ice exists in the permanently shadowed parts of craters in Mercury's north polar region.
  • NASA's Messenger spacecraft crash landed into Mercury after running out of fuel in April 2015, it surveyed the planet over a four year period gathering new data.
  • Mercury is usually very difficult to see in the night sky with the naked eye.

Spider Impact crater
Strange looking crater imaged by Messenger.
Mercury's Surface
The planet's colorless and cratered surface gives it a similar appearance to the moon, indeed like the moon it is covered in fine dust particles, between the craters there are smooth plains, mountains and valleys.
Mercury's Atmosphere
The planet has very little atmosphere, only tiny amounts of helium, hydrogen, oxygen and sodium. Because of the lack of atmosphere Mercury's sky is black with stars being visible during the day.
Mercury's Temperature
Mercury's lack of atmosphere leaves it unprotected from the sun's rays. The temperature on the planet may reach 450C (840F) during the day but at night the temperature may drop as low as -170C (-275F).

Mercury has no moons.
Life on Mercury
It is improbable that any form of life could exist in the harsh conditions.
Origin of Name
The Romans named the planet after the messenger to the gods.

Is Mercury Just Like the Moon?

surface of mercury
The cratered surface of Mercury.
Superficially Mercury seems very like the Moon, a long dead world with no atmosphere to speak of featuring extremely high temperatures during the day and freezing cold temperatures at night. The terrain also looks very similar, a highly cratered surface made up of a powdery grey dust. So what are the differences if any?

The first major difference is when you compare the density of the two worlds. Mercury’s density is much higher than the Moon’s and actually almost equal to Earth’s. This means that a portion of the planet would weigh only slightly less than an equal portion of Earth. This is because Mercury has a large iron core which accounts for 40% of its volume. Which brings us to the second major difference, it has an active molten iron core which means that like Earth and unlike the Moon it produces its own magnetic field, although the strength of the field is only around 1% of Earth’s. The third difference is that the force of gravity found on Mercury is more than twice as strong as that found on the Moon, the planet’s gravity is around two fifths of that we have on Earth. Lastly it has recently been discovered that the planet was far more volcanically active in its early history than previously thought, much more so than the Moon. Indeed the latest evidence indicates that there may have been geological activity up until 1 billion years ago, if this evidence is confirmed it would mean the planet would have much younger surface features than there are on the Moon.

Missions to Mercury
bepicolombo Launch: 2017
Arrival: 2024
Agency: ESA & JAXA
Summary: Two orbiters built by the ESA (Europe) and JAXA (Japan) which will hopefully gather a large range of data on its 1 year mission around the planet.
messenger Launch: August 2004
Arrival: March 2011
Agency: NASA
Summary: Messenger made three flybys of Mercury before making its orbital insertion in March 2011, the spacecraft undertook a comprehensive four year survey of the planet before crash landing into its north polar region in April 2015.
Mariner 10
mariner 10 Launch: November 1973
Arrival: March 1974
Agency: NASA
Summary:Mariner 10 was the first spacecraft to use "gravity assist", flying close to a planet to increase speed. It made 3 flybys during 1974-75 taking 3,500 images. It is believed to be still flying past the planet every 6 months.

crater impact
Crater impact.
Planet Mercury Statistics

Diameter: 3,032 miles (4,880 km)
Average Distance from Sun: 36 million miles (58 million km)
Orbital Period: 88 days
Rotation Period: 59 days

Maximum Surface Temperatures: 450C (840F)
Minimum Surface Temperatures: -170C (-275F)

Gravity: 3.7 m/s2 (38% Earth's Gravity)
Density: 5.427 g/cm3 (98.4% Earth's Density)
Mass: 3.3022 x 1023 kg (5.5% Earth's Mass)
Volume: 6.08272 x 1010 km3 (5.6% Earth's Volume)

Atmosphere: 42% Molecular oxygen, 29.0% sodium, 22.0% hydrogen, 6.0% helium, 0.5% potassium, Trace amounts of argon, nitrogen, carbon dioxide, water vapor, xenon, krypton and neon.

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