Neptune

Deep blue something

Neptune, the eighth and farthest known planet from the Sun in our Solar System, stands as a fascinating realm of intense blue hues and dynamic atmospheric activity. This ice giant, located an average distance of about 4.5 billion kilometers (2.8 billion miles) from the Sun, is renowned for its striking deep blue colour, which is even more vivid than that of Uranus. This coloration is attributed to the absorption of red light by methane in its atmosphere, as well as the possible presence of an unknown atmospheric constituent that enhances the blue shade.

Neptune's orbit around the Sun is incredibly lengthy, taking approximately 165 Earth years to complete a single revolution. In contrast, a day on Neptune is remarkably short, with the planet completing one rotation in about 16 hours. Despite its distance from the Sun, Neptune is host to a dynamic and active environment, including a complex system of moons, with Triton being the most notable among them.

Extreme storms

Neptune's beautiful blue atmosphere is perhaps the most turbulent and dynamic of all the planets. Like its more sedate neighbour, Uranus, it is composed primarily of hydrogen, helium, and methane. Methane absorbs red light, giving Neptune and Uranus their blue colour.

So why is the blue colour on Neptune so much deeper and more intense than on Uranus? Scientists believe the much stronger winds on Neptune whip up methane higher into the atmosphere and blow away much of the haze in the upper atmosphere. On Uranus, the deeper blues are hidden beneath high atmosphere clouds.

Neptune’s atmosphere is characterised by some of the fastest winds in the Solar System, reaching speeds of up to 2,100 kilometers per hour (1,300 miles per hour). That’s close to the speed of Concorde in its heyday!

Among the many wonders of Neptune's atmosphere, the Great Dark Spot stands out. This massive storm system, akin to Jupiter's Great Red Spot, was first spotted by the Voyager 2 spacecraft in 1989. The Great Dark Spot, a high-pressure system, appeared as a dark, elliptical shape. Although it has since vanished, the discovery of other similar storms suggests that Neptune's atmosphere is a realm of constant change and evolution.

Neptune's dynamic and active atmosphere is driven by internal processes which actually generate more heat than the planet receives from the Sun! This internal heat source likely arises from residual heat left over from the planet's formation and the slow gravitational compression of the planet's interior. These processes result in the release of energy, driving the intense weather patterns and storm systems observed on Neptune.

Interestingly, despite being farther from the Sun than Uranus, Neptune's internal heat makes it warmer than Uranus, contributing to its more dynamic atmospheric conditions.

Distant moons

Neptune has a collection of 14 known moons, with Triton being the largest and most intriguing. Triton is unique among the large moons of the Solar System due to its retrograde orbit, meaning it orbits Neptune in the opposite direction of the planet's rotation. This unusual orbit suggests that Triton was not formed in situ but was likely captured by Neptune's gravity.

Triton is a fascinating world in its own right, with a surface composed mostly of nitrogen ice and water ice. It has a thin atmosphere, primarily made up of nitrogen with trace amounts of methane. Triton's surface is marked by a variety of geological features, including geysers that erupt with nitrogen gas and dust, driven by seasonal heating from the distant Sun. These geysers are evidence of active geological processes occurring beneath Triton's icy crust.

The capture of Triton likely had significant consequences for Neptune's original moon system. Triton's capture could have led to gravitational disruptions that either ejected existing moons or caused them to collide and form new moons from the debris. This event would explain the relatively young surfaces of Neptune's other moons and their varied orbits.

Other notable moons of Neptune include Proteus, the second-largest moon, which is irregularly shaped and heavily cratered, and Nereid, known for its highly eccentric orbit. These moons, along with the smaller, inner moons, form a diverse and intriguing satellite system that continues to captivate astronomers.

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Beyond Neptune: Planet Nine

There used to be nine planets in the Solar System, but Pluto was reclassified as a dwarf planet in 2006, meaning Neptune is now the most distant directly observed planet.

But scientists now think there might be a new hidden ninth planet far away in our Solar System, imaginatively called Planet Nine. They believe this because some objects beyond Neptune, in an area called the Kuiper Belt, have strange and unusual orbits which don’t match the movements we expect. These orbits look like they are being pulled by the gravity of a big planet we can’t see yet. By studying the way these distant objects move, researchers think there could be a giant planet out there influencing them.

Planet Nine, if it exists, would be really far from the Sun, about 400 to 800 times farther than Earth is. In our scale model, with Neptune being 1.2km from the sun, Planet Nine would be over 16.4km away, or roughly the east side of Edinburgh. It would be much bigger than Earth, maybe 5 to 10 times as massive, and similar to Uranus and Neptune, with lots of ice and rock. It would be cold and dark and inhospitable, but it would also be a new planet, and that’s exciting!