In this blog post, we’ll examine the scientific basis and feasibility of the hypothesis that carbon transforms into diamonds under the extreme pressure and temperature conditions inside Neptune, potentially “raining down” like rain.
According to astronomers, Neptune is actually a planet that shouldn’t exist. In other words, Neptune’s very existence defies logic. It is said that when the solar system was forming, the region where Neptune now resides was too sparse in gas and dust. Consequently, calculations show that it would take over 10 billion years for a gas giant as massive as Neptune to form. However, the solar system is only about 4.6 billion years old. It’s a contradiction akin to a daughter being older than her father. This shocking contradiction is known as the “time scale problem.” The first person to present this calculation was Soviet astronomer Viktor Safronov, often called the father of modern planetary formation theory. However, time passed without this contradiction being resolved.
In 2005, the situation changed with the publication of a paper in *Nature*, one of the world’s most prestigious scientific journals. This paper explains that Neptune was born near Saturn, in a gas- and dust-rich “fertile zone” much closer to the Sun than it is today. Thanks to this, Neptune was able to grow rapidly in a short period of time, but it was later caught up in the intense gravitational tug-of-war between Jupiter and Saturn, pushed out to the outer reaches of the solar system, and settled into its current position. This study, conducted by four astronomers in Nice, France, is known as the “Nice Model” and is currently considered the most plausible scenario for Neptune’s formation.
When Voyager 2 first took close-up images of Neptune in 1989, scientists were shocked. This was because a massive dark spot—the “Great Dark Spot”—was discovered on the planet’s surface, large enough to fit an entire Earth inside it. Furthermore, Neptune is home to super-powerful winds reaching speeds of 2,100 km/h. This is an overwhelming level of wind speed, even when compared to the maximum wind speed of approximately 195 km/h recorded during Typhoon Maemi, which struck the Korean Peninsula in 2003. In such an environment, a human being would not simply be blown away but could be torn to pieces. However, when the Hubble Space Telescope observed Neptune again in 1994, this giant sunspot had vanished without a trace. Instead, a new sunspot appeared in a completely different location, and scientists have yet to fully uncover the mechanism behind this change.
The very fact that such powerful winds blow on Neptune is a mystery in itself. How is such energy generated in a place where sunlight barely reaches? While Neptune’s upper atmosphere is extremely cold, with temperatures as low as minus 214 degrees, the situation is completely different deeper inside. The internal temperature exceeds a staggering 5,000 degrees, causing Neptune to emit about 2.6 times more energy than it receives from the Sun. This extreme temperature difference creates massive convection, and since there are no terrain features to block it, the winds gradually accelerate to speeds approaching twice the speed of sound.
The deep blue Neptune we commonly imagine also differs somewhat from its actual appearance. This is because the photos taken by the Voyager spacecraft were adjusted with increased saturation and contrast to emphasize the features of the clouds and atmosphere. Neptune’s actual color is closer to a blue-green similar to that of Uranus. Neptune also has rings, but they are very dark and thin, making them difficult to observe. In particular, the “Adams Ring” is not a complete circle but exists as a broken, dotted line, which is believed to be due to the gravitational influence of the moon Galatea. Over time, some of these ring structures are gradually fading, and there is speculation that they may disappear entirely in the future.
In Neptune’s atmosphere, frozen methane forms clouds, and deep within the planet, carbon may transform into diamonds under ultra-high pressure, potentially resulting in “diamond rain.” These extreme conditions make Neptune an even more mysterious planet. Furthermore, its moon Triton also possesses very unique characteristics. Unlike typical moons, Triton is a “retrograde moon” that orbits in the opposite direction of the planet’s rotation; it is believed to be a celestial body that was originally in the Kuiper Belt and was captured by Neptune’s gravity. Currently, Triton is gradually being pulled toward Neptune, and it is expected that in billions of years, it will enter the Roche limit, shatter into pieces, and form a massive ring.
Furthermore, Neptune’s magnetic field is tilted by approximately 47 degrees relative to its rotational axis and exhibits a highly irregular structure with a significantly offset center. This is believed to be due to the presence of “superionic ice” within the planet; this substance exists in a unique state that possesses both solid and liquid properties, generating electricity and influencing the formation of the magnetic field.
To date, the only direct human exploration of Neptune was by Voyager 2 in 1989, and even that was merely a flyby observation rather than an orbital mission. This is because Neptune is so far away that the difficulty and cost of exploration are extremely high. As a result, there is still much we do not know about this planet. If the day ever comes when humanity can fully explore Neptune, the countless mysteries that have remained unsolved until now may be revealed one by one.
