Connect with us

Hi, what are you looking for?


Planet Guide: Mercury

I am pleased and excited to introduce a new series here at SkyFeed. While SkyFeed is primarily a space news resource, we will be posting regular resources about astronomy, space, and science. To start, we are focusing on planets in the Milky Way! 

Mercury is the closest planet to the Sun. It is 58 million kilometers (about 36 million miles) from the Sun. For comparison, our own planet is 150 million kilometers (93 million miles) from the sun. So, Mercury is significantly closer to the Sun than Earth is. 

Mercury is the smallest planet (excluding Pluto) in our solar system. It’s diameter measures in at 3,030 miles (roughly the same size as the United States). The radius is 2,440 km (1,516 miles) with a circumference at the equator of 15,329 km (9, 525 miles).

Mercury spins very slowly around it’s axis (how we calculate days). It takes 58.65 Earth days for Mercury to have one day. 


In 1973 the Mariner 10 spacecraft was the first sent to study Mercury. The spacecraft performed a flyby of the planet to collect information about the atmosphere, surface, and characteristics. Mariner 10’s biggest finds were discovering that Mercury has a weak magnetic field and that it has very cold nights (-183 degrees Celsius/ -297 degrees Fahrenheit) and very hot days (187 degrees Celsius/ 369 degrees Fahrenheit). 

In 2004 NASA launched the MESSENGER (Mercury Surface, Space Environment, Geochemistry and Ranging) spacecraft to Mercury and in 2011 it reached the planet. MESSENGER orbited and studied the Mercury for more than four years before it plummeted into the planet’s surface. 

MESSENGER was able to gather more in-depth information and photos to add onto the initial exploration data collected by Mariner 10! Because of MESSENGER’s mission, NASA was able to gather information about Mercury’s surface composition. According to NASA, the mission’s plan was to study the “geology, magnetic field, and chemical composition of the planet.” 

Mariner 10: NASA


Mercury has a solid surface with lots of impact craters. With all of the impact craters on it’s surface, it kind of looks like the moon! However, the composition of the planet is much different than the moon. 

During the MESSENGER mission, NASA scientists found “high concentrations of magnesium and calcium on Mercury’s night side, identifying a significant northward offset of Mercury’s magnetic field from the planet’s center, finding large amounts of water in Mercury’s exosphere, and revealing evidence of past volcanic activity on the surface.”

Check out this image taken by MESSENGER that shows evidence of lava flow at one point in Mercury’s past. 

Image: NASA/Johns Hopkins University Applied Physics
Laboratory/Carnegie Institution of Washington


Rather than an atmosphere, Mercury has an exosphere. An exosphere is the outer layer of an atmosphere. Mercury’s entire atmosphere is its exosphere. This is because there is so much activity from the Sun that disrupts Mercury’s atmosphere and makes it very thin. 

The Caltech Ask an Astronomer site explains it like this: “Mercury has an extremely thin atmosphere which is made up of atoms blasted off its surface by the Solar wind, a constant stream of particles coming from the outer layer of the Sun. Because Mercury is so hot, these atoms quickly escape into space. Unlike the stable atmospheres of Earth and Venus, Mercury’s atmosphere is constantly being replenished.”

Mercury’s exosphere is made up of oxygen, sodium, hydrogen, helium and potassium.


It only takes Mercury 88 Earth days to orbit around the sun. So, a year on Mercury is only 88 days.

To calculate your Mercury age take your age in years, multiply by 365 (the number of days in one Earth year) and divide by 88 (the number of days in a Mercury year) – that’s how old you are on Mercury!

Additionally, you could use this Age on other Planets Calculator from

Mercury sure is an interesting and underrated planet. Did you learn anything new about Mercury? Let us know down in the comments, on SkyFeed’s Instagram, or by @ing me on Twitter!

Advertisement Enter ad code here


You May Also Like