Discovery Dates of the Planets in Our Solar System

The planet Uranus has a day that lasts 17 Earth hours, and its year is equivalent to 84 Earth years.

The first five planets in our solar system have been identified for a long time since they are visible to the naked eye, making them difficult to date accurately.

The discovery date is unknown, but we do have the initial recorded date.

Each planet has changed over time and is considered an elder of the sky, overseeing every star, organism, and speck of dust in the entire solar system.

In this article, we will go through the discovery date of each planet, as well as some interesting facts about them.


Due to its visibility to the naked eye, Mercury does not have a definitive discovery date.

The Mul.Apin tablets contain the earliest recorded observations of the planet and were likely created by an Assyrian astronomer.

These tablets, which contain the largest surviving record of Babylonian stars and constellations, are believed to date back to 1000 BCE or earlier.

The cuneiform name used on these tablets for Mercury is Udu.Idim.Gu4.Ud, which translates to “the jumping planet.”

The Romans later named the planet Mercury after their messenger god because it moves across the sky faster than any other planet.

Mercury’s temperatures reach a scorching 840°F (450°C), and it is 18 times smaller than Earth with a diameter of 3,031 miles (4,878 km).

It orbits the Sun every 88 days, and one day on Mercury lasts just under 59 Earth days.

The Mariner 10 spacecraft was the first to visit Mercury, flying by in 1974 and 1975 and seeing less than half of the planet.

After that, no more was seen for over 30 years until NASA’s MESSENGER spacecraft flew by in 2008 and began orbiting the planet in 2011, sending photos back to Earth.


The oldest surviving astronomical document, a Babylonian text from 1600 BCE, contains the first written observation of Venus, spanning 21 years of its appearance in the sky.

Galileo Galilei, the first person to observe Venus through a telescope in 1610, noticed that the planet goes through moon-like phases, supporting the Copernican view that the planets orbit the Sun and not the Earth, as previously thought.

The surface of Venus reaches 900°F (480°C), it has no known moons, and it is 20% smaller than Earth.

One year on Venus is equivalent to 225 Earth days.

The symbol of Venus, ♀, is also a symbol of the female gender, and all but three of Venus’s surface features are named after famous women from around the world.


Of course, Earth was not discovered, since it is the planet we live on.

The first photo of Earth from space was taken on October 24, 1946, by a V-2 test rocket.

The debate over whether Earth is spherical or not has been going on for centuries. The concept was first introduced in Greek philosophy in the 6th century BC, but it wasn’t considered more than mere speculation until the Hellenistic astronomy backed it up in the 3rd century BC. It wasn’t until the Middle Ages that people started to believe that the Earth was indeed spherical. The conclusive proof of Earth’s spherical nature came from Ferdinand Magellan and Juan Sebastián Elcano’s voyage around the world between 1519 and 1522. Earth has four layers: the crust, mantle, outer core, and inner core, and is 70% water. Interestingly, if Earth were the size of a nickel, the sun would be as big as a front door.

Moving on to Mars, the first recorded observations of the planet were made by ancient Egyptian astronomers in the 2nd millennium BC. Aristotle weighed in on the debate around 300 BC, noting that Mars was further away than the moon after observing the moon passing in front of Mars. Galileo possibly had the first telescopic view of Mars between 1608 and 1610, but the first actual records were made by Francisco Fontana in 1636. Christian Huygens made the first informative Mars sketch in 1659. In 1965, NASA’s Mariner 4 sent back 22 close-up photos of Mars, making them the first close-up photos of any other planet outside Earth. Mars has a surface temperature averaging -81°F (-63°C) and is around 50% the size of Earth with 38% of the Earth’s gravity.

Jupiter has been known as the wandering star for centuries. The Babylonians recorded the first written records of Jupiter in the 7th/8th century BC. The Ancient Chinese split the sky into 12 zodiac regions, with Jupiter or “the Year Star” passing through one region each year by the 4th century BC. In 1610, Galileo discovered Jupiter’s four large moons known as the Galilean moons – Io, Europa, Ganymede, and Callisto. He also noted that the moons revolved around Jupiter, making it the first record of a center of motion not revolving around Earth. The first close-up photos of Jupiter were taken by the space probe Pioneer 10 in 1973, revealing the planet’s first real properties. Jupiter has an effective temperature of -234°F (-148°C), is the largest planet in our solar system, has 50 moons and 3 rings, and a fascinating storm that has been raging across its surface for hundreds of years. The planet also has drastically different gravity from Earth, meaning that if you weighed 100 lbs (45.4kg) on Earth, you would weigh 253 lbs (114.76kg) on Jupiter.

Finally, Saturn’s discovery date cannot be pinpointed, but it was first recorded by the Assyrians. The oldest records of Saturn describe it as a sparkle in the night around 700 BC. The Ancient Greeks named it Kronos, after the god of agriculture in 400 BC, which the Romans later renamed Saturnus.

In the early 1600s, Galileo believed Saturn was made up of three parts or a triple planet, but it wasn’t until over 40 years later that Christiaan Huygens realized the objects were actually rings made of rock and ice. Saturn has 53 moons, is 886 million miles from the sun, has an effective temperature of -288°F, and a year equivalent to 29 Earth years. Pioneer 11 took the first close-up images of Saturn.

Uranus was discovered in 1781 by Sir William Herschel and has a band of rings similar to Saturn. Voyager 2 is the only spacecraft to have flown by Uranus and discovered 10 new moons, a stronger magnetic field than Saturn, and two new rings. Uranus is a blue giant with a methane atmosphere and the largest tilt of any planet in our solar system. A day on Uranus lasts 17 Earth hours, and a year is equivalent to 84 Earth years.

Neptune was discovered in 1846 by John Couch Adams, who predicted its position through mathematical calculations. Neptune takes almost 165 Earth years to orbit the sun and was the first planet found through mathematical predictions. Its wind speeds can be nine times stronger than Earth’s.

Pluto was discovered by Clyde Tombaugh in 1930 after a sky survey, and its existence was theorized to explain anomalies in Uranus and Neptune’s orbits. It has been the subject of much debate about whether it should be considered a planet or not.

Tombaugh searched for the reason he was searching for in order to find Pluto. The planet was named after the Roman god and its name was suggested by an 11-year-old schoolgirl from Oxford, England. The New Horizons mission took the first high-res photographs of Pluto on July 14, 2015. In 2006, Pluto was no longer classified as a planet and is now the second-largest dwarf planet in our solar system and the second closest to the sun. Caltech researchers have discovered evidence of a possible “Planet X” deep in the solar system. This planet, also known as “Planet Nine”, could be as big as Neptune and has an orbit far beyond Pluto’s. The planet could have around 10 times the mass of Earth and its orbit could reach 20 times farther from the sun than Neptune. Despite the change in our perception of the solar system over time, each planet has its own unique tale, and the visible planets have been held in high regard in cultures and mythology around the world. Each planet has something incredible to learn about, and we have only just begun to scratch the surface.


1. When were the planets in our solar system first discovered?

The five planets visible to the naked eye have been known since ancient times. The ancient Babylonians, Greeks, and Chinese all recognized them and named them after their gods. Uranus was discovered in 1781 by William Herschel, and Neptune was discovered in 1846 by Johann Galle and Heinrich d’Arrest. Pluto, which was considered a planet until 2006, was discovered in 1930 by Clyde Tombaugh.

2. How were the planets discovered?

The visible planets were discovered through observation of the night sky. Uranus and Neptune were discovered through telescopes, as they are too far away to be seen with the naked eye. Pluto was discovered through photographic plates taken over several nights and then compared to see if any object had moved.

3. Were there any failed attempts at discovering planets?

Yes, there were several attempts to discover planets that were ultimately unsuccessful. For example, in the 19th century, astronomers believed there was a planet between Mercury and the Sun called Vulcan. However, it was later determined that the perturbations in Mercury’s orbit that led to the belief in Vulcan were actually caused by Einstein’s theory of general relativity.

4. Have any new planets been discovered in recent years?

Yes, several new planets have been discovered in recent years. In 2005, astronomers discovered Eris, which was originally thought to be larger than Pluto. Eris is now classified as a dwarf planet, as is Pluto. In 2015, NASA announced the discovery of Kepler-452b, a planet similar in size and orbit to Earth and in the habitable zone of its star.

5. Are there still undiscovered planets in our solar system?

It is possible that there are still undiscovered planets in our solar system, particularly in the outer reaches where they would be difficult to observe. In fact, astronomers have hypothesized the existence of a hypothetical “Planet Nine” beyond the orbit of Neptune, based on the unusual orbits of some trans-Neptunian objects.

6. What tools are used to discover planets?

The most common tool used to discover planets is the telescope, which allows astronomers to observe the night sky in detail. In recent years, space-based telescopes such as Kepler have been used to detect planets beyond our solar system. Other tools used in planet discovery include spectroscopy, which allows scientists to analyze the composition of a planet’s atmosphere, and gravitational lensing, which uses the gravitational pull of massive objects to bend and magnify light from more distant objects.

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