Due to its distance and composition, Neptune ranks as the only planet in the solar system not visible to the naked eye. As a result, this “ice giant” often gets forgotten when people think of the planets in the solar system. However, this fascinating world deserves more attention than it gets. The coldest and windiest planet in the solar system continues to mystify and captivate professional and amateur astronomers alike. That said, many people have never laid eyes on this most distant of plants, which begs the question, “What color is Neptune?” Keep reading to find out!
Background on Neptune
Neptune is the 8th planet in our solar system and the furthest planet from the Sun. It has a mass of 1.0243 x 10^26 kilograms, and its equatorial radius measures 24,764 kilometers. At those measurements, it ranks as the fourth-largest planet in the solar system by size and the third-most massive.
Neptune is composed mostly of gas and liquids and often gets lumped together with its near-twin, Uranus. Together, people often refer to Neptune and Uranus as the “ice giants” thanks to their primarily ice and rock interiors. Their solid interiors distinguish them from the other gas giants, Saturn and Jupiter.
Discovery of Neptune
Due to its distance and size, Neptune was the last planet to be officially discovered. Additionally, it ranks as the only planet in the solar system first found using mathematical predictions rather than empirical observation. That said, the earliest observations of Neptune date back to the early 1600s. Galileo Galilei plotted points that matched Neptune’s position in the sky on December 28, 1612, and January 27, 1613. However, Galilei thought that the object he observed in his telescope was a star, not a planet, so he doesn’t get credit for Neptune’s discovery.
French astronomer Alexis Bouvard published tables about the orbit of Uranus in 1821. Later observations of Uranus noted deviations from these original tables, which led Bouvard to surmise that another body’s gravity was interfering with the orbit of Uranus. This discovery prompted British astronomer John Couch Adams and French astronomer Urbain Le Verrier to undertake independent studies of the orbit of Uranus. Both astronomers came to the independent conclusion that another planet must be interfering with Uranus’s orbit.
Prompted by Le Verrier, German astronomer Johann Gottfried Galle scoured the night sky for signs of Neptune. Together with a student at the Berlin Observatory, Galle recorded the first official observation of Neptune on September 23, 1846. Galle found Neptune using predictions provided by Le Verrier of the planet’s location.
How Did Neptune Get its Name?
After its discovery, Neptune cycled through a series of temporary names. These included “Le Verrier’s planet,” after Urbain Le Verrier, while Johann Galle put forth the name “Janus” as a possible contender. In some circles, it just went by the name “the planet exterior to Uranus.”
In the hopes of claiming naming rights for the new planet, Le Verrier chose the name “Neptune.” He also proposed naming the planet after himself, but this idea was quickly shot down. Other prominent astronomers, such as Friedrich Georg Wilhelm von Struve, threw their support behind the name “Neptune.” The name quickly grew in acceptance and remains the name to this day.
Neptune is the god of the sea in Roman mythology and the counterpart of the Greek sea God Poseidon. The name Neptune keeps with the tradition of naming planets after Roman gods and goddesses.
Comparing Neptune and Earth
With a mass of 1.0243 x 10^26, Neptune possesses a mass nearly 17 times that of Earth. Similarly, its equatorial radius of 24,764 kilometers measures 4 times greater than that of Earth. Given its size, you could fit approximately 57 Earths inside Neptune. However, Neptune’s gravity near the surface measures relatively similarly to Earth’s at 11.15 meters per second squared.
In terms of structure, Neptune and Earth couldn’t be more different. Its upper atmosphere consists mostly of helium and hydrogen with some methane. This atmosphere makes up only 5 to 10% of Neptune’s mass but the vast majority of its volume. On the other hand, Neptune’s mantle is made up mostly of water, ammonia, and methane. Near the top of its clouds, temperatures reach -371 degrees Fahrenheit, while temperatures in its core can exceed 9,300 degrees Fahrenheit. Unlike Earth, Neptune also possesses a fragmented series of outer rings, known as arcs.
Neptune and Earth also rotate around an axis and around the Sun at different speeds. A day on Earth lasts approximately 24 hours, while a day on Neptune lasts a little over 16 hours. Meanwhile, Earth takes 1 year to orbit the Sun, while Neptune takes 164.79 years to orbit the sun. In fact, since it was first observed in 1846, Neptune has only completed one rotation around the Sun, which occurred back in 2011.
What Color is Neptune?
Neptune appears bright blue, which seems fitting given that it shares its name with the Roman god of the sea. The planet appears blue primarily due to the absorption of red and infrared light in Neptune’s atmosphere. Neptune’s lower atmosphere contains a large amount of methane, which tends to reflect blue wavelength light and traps red light. Clouds that rest above the lower atmosphere tend to look mostly light, while the highest parts of Neptune’s atmosphere can appear yellowish-red due to the absence of methane.
For years, scientists wondered why Neptune and Uranus didn’t look the same due to their similar composition. Neptune looks bluer, while Uranus appears cyan. Experts now believe this may be due to the thickness of the methane haze present in the atmosphere of both planets. This haze is thicker on Uranus than on Neptune, likely due to Neptune’s more active atmosphere. The strong winds on Neptune help to churn methane particles into methane snow in the lower atmosphere, which allows the methane to disperse. This makes the planet appear more blue compared to Uranus.
Is There Life on Neptune?
As far as we know, no life forms exist on Neptune. The planet’s cold temperature, pressure, and structure make it one of the least hospitable places for life to flourish.
That said, as you travel toward Neptune’s interior, pressure and temperatures increase. This means that – at some point – its icy core could turn to water. Where water exists, so can life. With this fact in mind, it is technically possible that life could exist somewhere within the core of Neptune. However, this is highly unlikely and extremely difficult to prove given that any water on Neptune only exists deep within its core.
A celestial body’s apparent magnitude measures its brightness as observed from Earth. The lower the number, the brighter it appears, while higher numbers appear dimmer. Most people struggle to see objects with an apparent magnitude greater than 6.5. That said, an apparent magnitude can vary depending on the viewer’s eyesight and atmospheric condition.
Due to its distance, you cannot view Neptune using only your naked eye. With an apparent magnitude of around 7.6, Neptune measures approximately one-fifth as bright as even the faintest stars that you can see in the night sky. If you wish to observe Neptune, you’ll need to purchase or use a telescope.
Neptune takes an incredibly long time to orbit the sun, which means it appears to move very slowly across the night sky. You can check star charts to confirm Neptune’s rough position in the night sky depending on the date. Using a telescope with a magnification of 100x you can see the blue color of Neptune. Switching to a magnification of 200x will also allow you to see Neptune’s disk-like shape. You’ll need a more powerful telescope to see the surface features of the planet, such as those used at universities and astronomical laboratories.
Exploration of Neptune
To date, only one space probe has directly explored Neptune. Launched on August 20, 1977, Voyager 2 was originally designed to study the outer solar system. It still ranks as the only spacecraft to study all of our solar system’s giant planets up close.
After studying Saturn, Jupiter, and Uranus, Voyager 2 made its way toward Neptune. It passed by the planet on August 25, 1989. The probe flew about 2,980 miles above the cloud tops of the planet. During its flyby, Voyager 2 managed to collect an incredible amount of data about the planet. It discovered 6 new moons (Despina, Galatea, Larissa, Naiad, Proteus, and Thalassa) and 4 new rings surrounding the planet. Voyager 2 also recorded strong winds up 1,200 miles on the planet’s surface and revealed details about its major features, including the Lesser Dark Spot, Great Dark Spot, and Scooter.
The photo featured at the top of this post is © iStock.com/3quarks
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