How Cold Is Neptune?

QUICK ANSWER

Neptune has an average cloud-top temperature of about -353°F (-214°C), one of the coldest places in our solar system. Despite the brutal cold, Neptune has the fastest winds of any planet, with speeds exceeding 1,500 mph at its equator. The internal heat that drives these winds is one of Neptune's defining features.

Neptune is cold, but it's also the windiest planet in the solar system. The combination is one of Neptune's bigger surprises: how does a planet so far from the Sun produce winds that exceed 1,500 mph? The answer is internal heat, which Neptune generates in abundance even though almost no sunlight reaches the planet.

How cold is Neptune's surface?

Average cloud-top temperature is about -353°F (-214°C). According to NASA, Neptune's upper atmosphere can drop as low as -373°F (-225°C) in some regions. The atmosphere gets warmer with depth, eventually reaching very high temperatures near the core (estimated around 9,000°F deep inside). The cloud tops are some of the coldest places in the solar system, though Uranus's upper atmosphere is actually slightly colder despite Uranus being closer to the Sun.

Why is Neptune so windy?

Internal heat drives it. Neptune emits about 2.6 times more energy than it receives from the Sun, a striking contrast with Uranus, which emits almost none. The excess heat comes from gravitational compression and leftover energy from the planet's formation. This internal heat drives powerful atmospheric circulation, creating winds that can reach speeds of 1,500 mph or more, the fastest sustained winds of any planet in our solar system. The wind speeds were one of Voyager 2's bigger surprises during the 1989 Neptune flyby.

What is the weather like on Neptune?

Wild and dynamic. Neptune has banded clouds (similar to Jupiter and Saturn but less dramatic), high-speed jet streams, and large storms that can persist for months or years. The Great Dark Spot, observed by Voyager 2 in 1989, was a storm roughly the size of Earth that disappeared by the time Hubble observed Neptune a few years later. Smaller dark spots have appeared and disappeared in subsequent observations. Bright white methane ice clouds drift above the deeper blue atmosphere, casting visible shadows in some Hubble images.

Does Neptune have seasons?

Yes, but they're enormously long. Neptune's axial tilt is about 28.3 degrees (similar to Earth's), but its 165-year orbit means each season lasts about 41 Earth years. Recent observations have detected real seasonal temperature changes on Neptune, though the effects are subtle because Neptune is so far from the Sun. A James Webb Space Telescope study in 2023 found that Neptune's south pole has been gradually cooling over the past two decades, a possible seasonal effect.

Neptune averages about -353°F at the cloud tops, one of the coldest places in our solar system. Despite the cold, the planet has the fastest winds in the solar system because Neptune generates substantial internal heat, unlike Uranus. The combination of brutal cold and supersonic winds makes Neptune's weather some of the most extreme in the solar system, even though it's so far from the Sun.

How Cold Is Neptune?