Guide Note

Mercury is closest planet to the Sun, and it is the smallest planet in the Solar System. Its proximity to the Sun gives the planet a huge range of temperatures. Because of its small size, cratered surface, and lack of a significant atmosphere, Mercury is often compared to Earth's Moon.¹

Fast Facts

1. Smallest planet in the Solar System
2. Discovered in ancient times
3. Named after the Roman god of commerce
4. Radius: 2,440 kilometers (46% of Earth's)
5. Circumference: 15,329 kilometers
6. Surface area: 74.8 million square kilometers (11% of Earth's)
7. Mass: 3.30x10²³ kilograms
8. Average distance from the Sun: 57.9 million kilometers
9. No moons in its orbit
10. Temperature ranges between -173 and 427 degrees Celcius (-279 and 801 degrees Fahrenheit²
11. Atmosphere is extremely thin
12. Atmospheric content:
    1. Oxygen: 42%
    2. Sodium: 29%
    3. Hydrogen: 22%
    4. Helium: 6%
    5. Potassium: 0.5%
    6. Trace amounts of Argon, Carbon Dioxide, Water, Nitrogen, Xenon, Krypton, Neon³

Quotes

"Scientists say the pictures reveal that the planet once had active volcanoes, and that Mercury is shrinking as it ages, leaving ridges reminiscent of wrinkles—strange features that may be a product of the planet's shrinking, cooling core."⁴

"The spacecraft also discovered a unique feature that scientists dubbed "The Spider." This formation never has been seen on Mercury before and nothing like it has been observed on the moon." ⁵