When Was Mercury Discovered?
Written by Fraser Cain
Mercury's limb. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Mercury is one of the 5 planets visible with the unaided eye. Even thousands of years ago, ancient astronomers knew that the 5 wanderers were different from the other stars in the sky. The 5 planets visible with the unaided eye are Mercury, Venus, Mars, Jupiter and Saturn. They gave them distinct names, and charted their positions with incredible accuracy. It's impossible to say "when was Mercury discovered", since that would have been before recorded history.
It probably wasn't until the Copernican model was developed – that the planets are believed to travel around the Sun – that astronomers really understood that Mercury was another planet; just like the Earth. Copernicus published his model in 1543, describing how the Earth was just another planet orbiting the Sun.
This model was backed up by Galileo, who pointed his first rudimentary telescope at Mercury in the 17th century. Unfortunately his telescope wasn't powerful enough to see Mercury go through phases like he saw with Venus.
Because it's so small and close to the Sun, Mercury was difficult to observe with ground-based telescopes. More powerful telescopes only revealed a small grey disk; they didn't have the resolution to display features on the planet's surface, like craters or lava fields.
It wasn't until the early 1960s when radio astronomers started bouncing signals off the surface of Mercury that more information was finally known about the planet. These signals revealed that Mercury's day length is about 59 days. Even more detailed observations have been made with the Arecibo telescope, mapping surface features down to a resolution of 5 km.
The most detailed observations of Mercury have come from the exploration from spacecraft sent from Earth. NASA's Mariner 10 spacecraft swept past Mercury in 1974, capturing images from an altitude of just 327 km. It eventually mapped about half of the planet in unprecedented detail, revealing that the planet looked very similar to the Earth's moon, with many impact craters and ancient lava fields.
If you were wondering when the element Mercury was discovered, it was also known for thousands of years. Mercury was found in Egyptian tombs that date back almost 4,000 years ago.
We have written many articles about Mercury for Universe Today. Here's an article about new mysteries unveiled on Mercury, and the possibility that Mercury could cause an interplanetary smash-up.
Want more information on Mercury? Here's a link to NASA's World Book on Mercury, and here's NASA's Solar System Exploration Guide to Mercury.
We have also recorded a whole episode of Astronomy Cast that's just about planet Mercury. Listen to it here, Episode 49: Mercury.
Filed under: Astronomy
