Mercury: Quick Facts

Updated on July 23, 2019
Larry Slawson profile image

Larry Slawson received his Masters Degree at UNC Charlotte. He specializes in Russian and Ukrainian History.

The planet Mercury (Image taken by MARINER).
The planet Mercury (Image taken by MARINER). | Source

Scientific Properties of the Planet Mercury

Orbital Semimajor Axis: 0.39 Astronomical Units (57.9 Million Kilometers)

Orbital Eccentricity: 0.206

Perihelion: 0.31 Astronomical Units (46 Million Kilometers)

Aphelion: 0.47 Astronomical Units (69.8 Million Kilometers)

Mean Orbital Speed: 47.9 Kilometers Per Second

Sidereal Oribital Period: 88 Solar Days (0.241 Tropical Years)

Synodic Orbital Period: 115.9 Days (Solar)

Orbital Inclination to the Ecliptic: 7.00 Degrees

Greatest Angular Diameter (As Viewed From Earth): 13”

Overall Mass: 3.30 x 1023 Kilograms (0.055 of Earth’s Mass)

Equatorial Radius: 2,440 Kilometers (0.38 the Equatorial Radius of Earth)

Mean/Average Density: 5,430 Kilograms per Meters Cubed (0.98 of Earth’s Mean Density)

Surface Gravity: 3.70 Meters Per Second Squared (0.38 of Earth’s Surface Gravity)

Escape Speed/Velocity: 4.2 Kilometers Per Second

Sidereal Rotation Period: 58.6 Days (Solar)

Axial Tilt: 0.0 Degrees

Surface Magnetic Field: 0.011 of Earth’s Magnetic Field

Magnetic Axis Tilt Relative to Rotation Axis: <10 Degrees

Mean/Average Surface Temperature: 100-700 Kelvins (-279.67 Degrees Fahrenheit to 800.33 Degrees Fahrenheit)

Total Number of Moons/Satellites: 0

Internal structure of the planet Mercury. Notice its exceptionally large core that dominates much of its overall structure.
Internal structure of the planet Mercury. Notice its exceptionally large core that dominates much of its overall structure. | Source

Quick Facts About Mercury

Fact #1: Due to its close proximity to the Sun, one year on Mercury is equal to eighty-eight days. Despite this short amount of time, Mercury’s days are quite long due to its slow rotation rate (an effect of the Sun’s gravitational pull). One solar day (noon to noon) is equivalent to 176 days on Earth, whereas the sidereal day is equivalent to 59 days on Earth.

Fact #2: Despite the planet’s small size, Mercury is one of the densest planets (second to Earth). Scientists believe that this is because the planet is composed primarily of heavy rocks and metals. It is also believed that Mercury possesses a molten core. Although scientists previously believed the core to be composed primarily of iron, they now believe that it is composed of sulfur instead. Altogether, Mercury’s core makes up around forty-two percent of its total volume/density (compared to Earth’s core, which comprises only seventeen percent of its volume).

Fact #3: Despite its close proximity to the Sun, Mercury is not the hottest planet. Venus (the second planet in our solar system) is actually the hottest planet due to its intense atmosphere. Mercury, in contrast, possesses no atmosphere to trap and regulate heat. This helps to explain the wide temperature fluctuations on Mercury which range from 427 Degrees Celsius (on the side facing the Sun), to temperatures as low as -173 Degrees Celsius (on the dark side of the planet).

Fact #4: Mercury has often been compared to the Moon due to its geographical similarities; particularly its “cratered” look. Craters dominate much of Mercury’s surface, indicating a violent history of collisions with asteroids, meteors, and comets in its past. The biggest crater on Mercury is known as the Caloris Basin and is approximately 1,550 kilometers in diameter. This crater was first discovered by Mariner 10 in 1974.

Fact #5: Due to the planet’s close proximity to the Sun, Mercury is a difficult planet to explore. As a result, only two spacecraft have been able to scout the planet. Mariner 10 conducted three flybys between 1974 and 1975, and helped scientists to map out a considerable amount of the planet’s surface. More recently, NASA launched the “Messenger” probe (3 August 2004) to return to the planet for additional study.

Fact #6: It is unknown who (or when) the planet Mercury was first discovered. However, many scholars and scientists, alike, believe that the Sumerians (around 3,000 B.C.) may have been the first people to record the planet. It wasn’t until 1543, however, that astronomers recognized Mercury as a planet (rather than a star). The planet garnered its name from the Roman messenger to the gods (also known as Hermes in Greek mythology).

"I had rather be Mercury, the smallest among seven [planets], revolving around the Sun than the first among five [moons] revolving around Saturn."

— Johann Wolfgang von Goethe

Fun Facts about Mercury

Fun Fact #1: Mercury’s orbital speed is extremely fast (compared to other planets). As a result, early civilizations were convinced that Mercury was actually a second star in our solar system.

Fun Fact #2: Mercury continues to be the smallest planet in the solar system. Its diameter is only 4,879 kilometers. Despite its small size, Mercury remains one of five planets that can be observed with the naked eye.

Fun Fact #3: Mercury’s gravity is only thirty eight percent of Earth’s gravitational pull. As a result, the planet is incapable of maintaining a stable atmosphere, and possesses no seasonal variations. This also helps explain why the planet possesses no rings or moons.

Fun Fact #4: While most of the planets in our solar system maintain relatively circular orbits around the Sun, Mercury’s orbit follows an elliptical and elongated pattern as it rotates around the Sun. At times, the planet reaches as close as 29 million miles (47 million kilometers) from the Sun, and as far as 43 million miles (70 million kilometers) at other times of its orbit.

Fun Fact #5: The outer shell (crust) of Mercury is relatively thin. Altogether the crust is believed to be only 500 to 600 kilometers thick (approximately 310 to 375 miles). This is in stark contrast to Earth’s outer crust and mantle which is 2,930 kilometers (or 1,819 miles) thick.

Fun Fact #6: Mercury maintains an extremely weak magnetic field. In contrast to Earth, Mercury’s magnetic field is only one percent the strength of Earth’s.

Fun Fact #7: Many scientists now believe that Mercury’s craters contain ice; particularly on the planet’s north and south poles which are cold and relatively shadowy. It is believed that this ice may have formed from water vapor beneath the ground, or was delivered by comets and meteorites after impacting the planet’s surface.

Fun Fact #8: In addition to the possibility of ice, some scientists believe that Mercury may have been covered in volcanoes at one point in its history. According to images delivered by the “Messenger” probe, the northern plains of the planet appear smooth across its surface; indicating the possible presence of dried lava beds. This, according to scientists, would help explain many of the other smooth locations across Mercury’s surface, as well as the smooth appearance of several of its craters.

Fun Fact #9: On 20 October 2018, the ESA launched two additional orbiters to study the planet Mercury. The BepiColombo contains both the ESA’s Mercury Planetary Orbiter, as well as Japan’s Mercury Magnetosphere Orbiter. BepiColombo is scheduled to enter Mercury’s orbit in 2025 after completing two Venus flybys. The spacecraft will conduct six flyby missions across Mercury’s orbit.

Fun Fact #10: Although it remains unclear how the planet Mercury formed, many scientists believe that the planet developed around 4.5 billion years ago. Scientists and astronomers alike argue that the planet appears to have formed as a result of gravity pulling hot gas and dust together.

Up-close view of Mercury's surface. Notice how the planet is dotted with meteor and asteroid craters.
Up-close view of Mercury's surface. Notice how the planet is dotted with meteor and asteroid craters. | Source


Although small, Mercury continues to play a large role in the scientific community as more and more information is gleaned from space probes about its inner and outer structures and origins. As additional spacecraft, such as the BepiColombo, make additional flybys around the planet, it will be interesting to see what new information can be learned about this fascinating member of our solar system, and if this planet holds additional clues to understanding the galaxy and universe at large.

Were any of these facts and figures surprising to you?

See results

Works Cited:


Wikipedia contributors, "Mercury (planet)," Wikipedia, The Free Encyclopedia, (accessed January 3, 2019).

Questions & Answers

    © 2019 Larry Slawson


      0 of 8192 characters used
      Post Comment
      • Larry Slawson profile imageAUTHOR

        Larry Slawson 

        12 months ago from North Carolina

        Thank you Liz! I'm glad you enjoyed!

      • Eurofile profile image

        Liz Westwood 

        12 months ago from UK

        This is a great reference article, packed with information.

      • Larry Slawson profile imageAUTHOR

        Larry Slawson 

        12 months ago from North Carolina

        I’m glad both of you enjoyed. I’ve been reading more astronomy related material these past few weeks. Really fascinating stuff.

      • Guckenberger profile image

        Alexander James Guckenberger 

        12 months ago from Maryland, United States of America

        I love astronomy.

      • Pamela99 profile image

        Pamela Oglesby 

        12 months ago from Sunny Florida

        This is such an interesting article about Mercury. I never thought any ice would be anywhere on Mercury. Each of the facts was interesting.


      This website uses cookies

      As a user in the EEA, your approval is needed on a few things. To provide a better website experience, uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

      For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at:

      Show Details
      HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
      LoginThis is necessary to sign in to the HubPages Service.
      Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
      AkismetThis is used to detect comment spam. (Privacy Policy)
      HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
      HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
      Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
      CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
      Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the or domains, for performance and efficiency reasons. (Privacy Policy)
      Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
      Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
      Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
      Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
      Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
      VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
      PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
      Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
      MavenThis supports the Maven widget and search functionality. (Privacy Policy)
      Google AdSenseThis is an ad network. (Privacy Policy)
      Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
      Index ExchangeThis is an ad network. (Privacy Policy)
      SovrnThis is an ad network. (Privacy Policy)
      Facebook AdsThis is an ad network. (Privacy Policy)
      Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
      AppNexusThis is an ad network. (Privacy Policy)
      OpenxThis is an ad network. (Privacy Policy)
      Rubicon ProjectThis is an ad network. (Privacy Policy)
      TripleLiftThis is an ad network. (Privacy Policy)
      Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
      Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
      Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
      Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
      ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
      Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)
      ClickscoThis is a data management platform studying reader behavior (Privacy Policy)