Skip Navigation

14.7: Mercury

Difficulty Level: At Grade Created by: CK-12
Atoms Practice
Estimated3 minsto complete
Practice Mercury
This indicates how strong in your memory this concept is
Estimated3 minsto complete
Estimated3 minsto complete
Practice Now
This indicates how strong in your memory this concept is
Turn In

How did tiny Mercury get its name?

Mercury was named for the Roman messenger god who traveled rapidly on his winged sandals. From the vantage point of Earth, the planet Mercury travels swiftly across the face of the Sun.


The smallest planet, Mercury, is the planet closest to the Sun. Because Mercury is so close to the Sun, it is difficult to observe from Earth, even with a telescope. However, the Mariner 10 spacecraft, shown in Figure below, visited Mercury from 1974 to 1975.

The MESSENGER spacecraft has been studying Mercury in detail since 2005. The craft is currently in orbit around the planet, where it is creating detailed maps. MESSENGER stands for Mercury Surface, Space Environment, Geochemistry and Ranging.

(a) Mariner 10 made three flybys of Mercury in 1974 and 1975. (b) A 2008 image of compiled from a flyby by MESSENGER.

As Figure below shows, the surface of Mercury is covered with craters, like Earth’s moon. Ancient impact craters means that for billions of years Mercury hasn’t changed much geologically. Also, with very little atmosphere, the processes of weathering and erosion do not wear down structures on the planet.

Mercury is covered with craters, like Earth’s moon. MESSENGER has taken extremely detailed pictures of the planet’s surface.

There are many images, movies, and activities on the MESSENGER site: http://messenger.jhuapl.edu/index.php

Short Year, Long Days

Mercury is named for the Roman messenger god, who could run extremely quickly, just as the planet moves very quickly in its orbit around the Sun. A year on Mercury — the length of time it takes to orbit the Sun — is just 88 Earth days.

Despite its very short years, Mercury has very long days. A day is defined as the time it takes a planet to turn on its axis. Mercury rotates slowly on its axis, turning exactly three times for every two times it orbits the Sun. Therefore, each day on Mercury is 57 Earth days long. In other words, on Mercury, a year is only a Mercury day and a half long!

Extreme Temperatures

Mercury is close to the Sun, so it can get very hot. However, Mercury has virtually no atmosphere, no water to insulate the surface, and it rotates very slowly. For these reasons, temperatures on the surface of Mercury vary widely. In direct sunlight, the surface can be as hot as 427oC (801oF). On the dark side, or in the shadows inside craters, the surface can be as cold as -183oC (-297oF)! Although most of Mercury is extremely dry, scientists think there may be a small amount of water in the form of ice at the poles of Mercury, in areas that never receive direct sunlight.

A Liquid Metal Core

Figure below shows a diagram of Mercury’s interior. Mercury is one of the densest planets. It’s relatively large, liquid core, made mostly of melted iron, takes up about 42% of the planet's volume.

Mercury contains a thin crust, a mantle, and a large, liquid core that is rich in iron.


  • Mercury appears to be moving rapidly because it's so close to the Sun.
  • Mercury has short years, just 88 Earth days, but long days, about 57 Earth days.
  • Mercury is extremely hot and has a liquid metal core.


Use this resource to answer the questions that follow.


1. What probe was sent to Mercury?

2. How does Mercury compare in size to the other planets?

3. Why does Mercury have a large core?

4. Describe the temperature variations on Mercury.

5. How long does a day last on Mercury?

6. What is the evidence of volcanic activity on Mercury?

7. Why do scientists think there may be ice on Mercury?

8. Why can't the Hubble Space Telescope be used to view Mercury?

Want to know more about Mercury? See https://www.windows2universe.org/mercury/mercury.html&edu=high.


1. Why is a year on Mercury only 88 days long?

2. Why is Mercury mostly really hot, but very cold in spots?

3. Think about the formation of the solar system. Why is Mercury the densest planet?

Notes/Highlights Having trouble? Report an issue.

Color Highlighted Text Notes
Show More

Image Attributions

Show Hide Details
Difficulty Level:
At Grade

Concept Nodes:

Date Created:
Feb 24, 2012
Last Modified:
Aug 07, 2016
Files can only be attached to the latest version of Modality
Please wait...
Please wait...
Image Detail
Sizes: Medium | Original