Neptune is perhaps one of the most fascinating planets in the solar system, maybe because we know very little about this planet. Due to its immense distance from the Sun, it has not been visited more than once.
The earliest known observation of Neptune can be found in Galileo’s drawings dated back to 28 December 1612, which consist of markings that are consistent with the currently known position of the planet. However, Galileo mistook it for a fixed star in the night sky. It was Urbain Le Verrier and John Couch Adams who first predicted its existence in 1845-46 and calculated the position of Neptune independently.
Below, we have compiled a list of 14 facts about Neptune that you might find really interesting.
Discovered In: 23 September 1846
Equatorial Diameter: 49,244 km
Mass: 1.02413×1026 kg
Density: 1.683 g/cm
Surface Gravity: 11.15 m/s²
Satellites or Moons: 14
14. Neptune is the Most Distant Planet
Outer planets in our solar system | Image Courtesy: Wikimedia Commons
Following its discovery in 1846, Neptune became the farthest planet in the solar system. The planet surrendered its position in 1930 to the newly discovered Pluto, however not entirely.
As you may know, Pluto has an extremely elliptical orbit, due to which it periodically moves closer to the Sun than Neptune. The last time Neptune went farther than Pluto was in 1979 and it remained that way until 1999. During that period of time, Neptune was the farthest planet in the solar system.
A final twist in this story came in 2006, when the International Astronomical Union IAU changed Pluto status to a dwarf planet, making Neptune officially the farthest planet once again.
13. It’s Not the Coldest Planet in our Solar System
Neptune’s outer atmosphere is one of the coldest places in the solar system, with temperatures approaching near 55 K or −218 °C. However, despite being the farthest planet from the Sun, Neptune is not the coldest planet in the solar system. That title goes to Uranus where temperature can reach as low as 49 K (-224 °C).
While the surface temperatures of two planets are almost identical, the upper regions of Neptune’s troposphere are relatively hotter than that of Uranus’. The reason behind this discrepancy is Neptune’s higher internal heating.
Uranus, which is more than 1 billion km closer to the Sun than Neptune, radiates only 1.1 times the heat it receives from the Sun (it’s still a mystery). On the other hand, Neptune radiates as much as 2.61 times the heat it receives from the Sun. Despite being the farthest planet in the solar system, Neptune has enough internal energy to drive the fastest and most powerful winds in the solar system.
12. How Many Moon Does Neptune Have?
A total of 14 natural satellites have been identified orbiting around the planet Neptune all of which are named after water deities in Greek mythology in accordance with Neptune’s status as the god of the sea.
Triton (don’t confuse it with Saturn’s moon Titan) is the most well known and largest of all Neptunian moons and was discovered by English astronomer William Lassell on October 10, 1846, exactly 17 days after Neptune’s discovery. One of its moon, Nereid, has one of the least circular orbits of any natural satellite in the solar system.
After Triton, the second most massive moon in the Neptunian system is Proteus (though it’s only 0.25% of the mass of Triton). Proteus is noteworthy because of its irregular shape, despite being large enough to be pulled by its own gravity into a sphere. It was discovered by Voyager 2 in 1989 along with four innermost moons of Neptune.
11. It Also Has A Planetary Ring System
The full view of the Neptunian ring system with the highest possible sensitivity. | Image Courtesy: NASA
Like the other three gas giants, Neptune also has a full-fledged ring system, though it’s less significant than that of Saturn’s. The Neptunian rings system consist of five major rings, all of which were initially discovered by a team of astronomers at La Silla Observatory in 1984.
These rings are extremely dark and are mainly composed of dust and small rocks. The composition of dust can range from 20% to as high 70%. Their density is comparable to that of the rings around the planet Jupiter.
Studies have suggested that the rings of Neptune are significantly younger than the age of our solar system and most probably a result of the fragmentation of onetime moons after their collision.
Observations from Earth-based telescopes have indicated that Neptunian rings are highly unstable. Images taken by the W.M. Keck Observatory in 2002-03 revealed a considerable amount of decay in the rings of Neptune when compared to the data taken by Voyager 2. It’s been estimated that one of the Neptunian rings might disappear in less than 100 years.
10. Triton is Probably A Captured Moon
This image of Neptune and its largest moon Triton was captured by Voyager 2 few days before its closest approach to the planet.
Triton is the only natural satellite (of considerable size) in the solar system that revolves in a retrograde orbit — it revolves in the opposite direction in relation to Neptune’s other moons. The best possible explanation for this phenomenon is that Triton’s origin is completely different from other moons of Neptune and was acquired by the planet at some point during its history.
This theory is well supported by the uneven distribution of mass in the Neptune’s satellite system, which coincidentally is more or less similar to that of Saturn’s. Its largest moon, Triton makes up more than 99% of the total mass of the system while the rest are accountable for just 0.3%.
This lopsidedness is an indication that Triton was captured by Neptune after the formation of its Primordial satellite system, a large part of which would have been decimated during the process.
9. Triton is Likely To Turn Into A New Ring System
Triton’s rotation is synchronous (tidally locked) with the orbit of Neptune — one side of the moon faces the planet at all times. Due to extensive tidal interaction, Triton’s orbit is gradually coming closer to Neptune and will continue to decay further. At the moment, Triton is closer to Neptune than the Moon is to Earth.
According to an estimation, it will take about 3.6 billion years for Triton to pass through Neptune’s Roche Limit and is likely to disintegrate and create a new ring system around the planet.
8. Neptune Has Been Visited Only Once
An artist’s concept of Voyager 2
NASA’s Voyager 2 is the only space probe that has ever visited the far-flung planet. For many years, Neptune and two of its larger moons have been observed with the help of ground-based telescopes, but, it was only after Voyager 2 that researchers have been able to study the planet more closely and accurately.
During its time in the Neptunian system, the probe acquired numerous valuable data on the planet’s upper atmosphere/magnetosphere and helped researchers discover previously unknown rings around the planet. Most of the data collected by Voyager 2 is still considered the best available information on the planet even after the emergence of advanced space-based telescopes.
The probe confirmed the presence of a magnetic field around the planet and that it is tilted or off center, similar to that of Uranus. Using radio-emission signals, it discovered an active weather pattern on the planet and determined its rotation period.
Furthermore, Voyager 2 allowed researchers to obtain Neptune’s mass with more precision which turned out be 0.5 percent less than previously thought.
7. Neptune is the Smallest of All Gas Giants
The four outer planets in the solar system are called gas giants since they are composed of gasses namely hydrogen and helium and in the case of Neptune with traces of nitrogen and hydrocarbons. Jupiter is undoubtedly the largest of all gas giants (and the largest planet in the solar system), but do you know which outer planet is the smallest one? The answer is Neptune.
Yes, with an equatorial diameter of just 24,244 km, Neptune is smaller than all other gas giants including the planet Uranus. Here is an interesting fact, Neptune is actually more massive than Uranus and thus have a slightly higher density than its almost near twin planet. In fact, Neptune is the densest gas giant (1.638 g/cm3).
6. Neptune Has the Strongest Winds in the Solar System
High altitude clouds on Neptune | Image taken by Voyager 2 just before its closest approach to the planet
Unlike hazy and mostly featureless atmosphere of Uranus, Neptune’s atmosphere is dynamic and has visible weather patterns. These weather patterns are fueled by violent wind speeds as high as 1,300 mph or 2,100 km/h and it happens to be the strongest in the entire solar system.
After carefully analyzing clouds and prevalent wind pattern, researchers were able to discover apparent regional variations in the wind speeds on the planet. For instance, at cloud tops, the average wind speed near the equatorial region is 400 m/s, whereas near the poles it is 250 m/s.
On Neptune, the general direction at which wind is blowing is opposite to the planet’s rotation. Winds moving towards the west (at 325 m/s) are as much as 16 times much stronger than eastbound winds (20 m/s).
5. Mysterious Tale of The Great Dark Spot
The Great Dark Spot (on top) along with two other active storms on Neptune during Voyager 2’s close flyby
In 1989, during its flyby, Voyager 2 discovered a giant anti-cyclonic storm on Neptune, which was eventually named the Great Dark Spot (GDS). However, when the planet was photographed by the Hubble Space Telescope in 1994, it had mysteriously disappeared.
The Great Dark Spot of Neptune was more or less about the same size as the Earth. It was identical to Jupiter’s Great Red Spot, however, unlike the one on Jupiter, the interiors of the Dark Spot are relatively cloud free and have shorter life spans.
Neptune was again photographed in 2016, but this time an almost identical dark spot appeared on the planet’s northern hemisphere. The new spot is called the Northern Great Dark Spot (NGDS).
Researchers believe that, like the GDS, few former dark spots which are no longer visible may still exist as cyclones (but without the dark feature). These spots may vanish when they reach too close to the equator.
Few Quick Facts
4. Neptune’s atmosphere is composed of 80% hydrogen and 19% helium along with trace amount of methane. As is the case with Uranus, Neptune’s blue appearance is due to the absorption of sunlight by the atmospheric methane.
However, as you can see, Neptune’s vivid blue shade differs from Uranus’ mild cyan color and since both Neptune and Uranus have similar methane content present in their atmosphere, researchers believe that an unknown element is responsible for Neptune’s color.
A combined near-infrared and color image of Neptune along with four of its moons | Image Courtesy: NASA, STScI
3. Neptune’s Triton is one of the five natural satellites in the Solar System that are geologically active, other being Saturn’s Triton and Enceladus, and Jupiter’s Io and Europa. Moreover, Triton is the only Neptunian moon large enough to be in hydrostatic equilibrium.
2. Since Voyager 2, no other space probe has made a close flyby of the planet till date. However, there are few proposed space missions that will study the planet in the near future. One such mission is NASA’s Argo, which will make flybys of Jupiter, Saturn, Neptune, and its moon Triton before launching itself to study Kuiper Belt objects.
The Trident is another proposed space mission concept that will make close flybys of Jupiter and Neptune (by 2038). Trident’s main focus will be Triton, where it will closely study ongoing volcanic activity and collect evidence of any existing oceanic body on the moon.
1. While observing the Great Dark Spot from the data taken by the Voyager 2, researchers spotted a new cyclonic storm further south of the GDS’ location.
During the time of its observation, the cyclone was moving much faster than the Great Dark Spot. It was small and featured white clouds rather than dark like the GDS. Inspired by these characteristics, the storm was named The Scooter.