How Cold Is Neptune?

How cold is Neptune

Neptune is the furthest planet from the Sun in our solar system. However, despite the planet’s vast distance from the star, it is not actually the coldest.

Similarly to Earth, Neptune is warmer at times and colder during other times, as it goes through ‘seasons’ each Neptunian year.

The planet's average temperature is 59 Kelvin or -353 Fahrenheit! As the planet is such a huge distance away from the Sun, the ice giant takes in hardly any heat from it.

In fact, the temperature on Neptune is determined more so by the motions within its interior (these help carry heat from the inside of a planet to the outside), than from the Sun’s rays.

Neptune isn’t parallel to the Sun, much like other planets in our solar system. Rather it is slightly tilted to one side at an angle slightly steeper than Earth is tilted. This is what causes both planets to experience ‘seasons’.

On average, the gas giant is around 2.8 billion miles from the sun, resulting in its pole reaching higher temperatures than other areas of the planet. This is because the pole is tipped towards the Sun.

This only happens for one quarter of a Neptunian year, which is what creates the ‘seasonal’ temperature changes.

Like other gas giants, Neptune still holds a lot of the atmosphere it had during its formation

On Neptune, pressure and temperature changes at different heights. So, at the top of the clouds, the average temperature is 63.1 Kelvin or -346 Fahrenheit.

On Neptune’s surface, the pressure is thought to be the equivalent of the pressure at sea level on Earth. The temperature at this point is also thought to be about 63.1 Kelvin or -346 Fahrenheit.

As an ‘ice giant’, it is heavily made up of ices. You may have wondered if the planet’s blueish color was a by-product of the freezing temperatures but, it’s actually the hydrogen, helium and traces of methane that make up  Neptune's atmosphere that creates its blueish color.

Much like Uranus and other gas giants, Neptune does not have a solid surface. Rather, its gaseous surface goes from the top of the planet all the way down to its mantle, which is made up of a sort of water-ammonia ocean.

Why is it so cold on Neptune?

Neptune is home to some of the most extreme weather conditions in the entire solar system.

As the eighth planet in the solar system and furthest from the Sun, Neptune takes in very little heat from the star. Instead, the planet’s internal motions contribute more to temperature changes.

One of the main reasons why Neptune is so cold, is because of its distance from the Sun. It is estimated to be about 2.8 billion miles away from the heat-giving star. Moreover, Neptune is also not parallel to the Sun, much like other planets in our solar system.

It is tilted on one side, so the area that is out of line with the Sun is significantly colder than the part of its surface that is tilted towards it. This is what creates the ‘seasonal’ differences in temperature on the planet.

It is actually tilted in a similar way that Earth is tilted, albeit at a steeper angle. So, although Neptune is extremely cold, there are parts of the planet that experience warmer temperatures.

Not only is the temperature temperamental, but the planet can experience crazy weather. It can generate winds of up to 1,305 miles per hour! This is nine times faster than winds felt on Earth and three times faster than winds on Jupiter. 

These winds generate incredibly strong storms. For example, when we observed the planet back in 1989 on the Voyager 2 mission, we saw a storm that equalled about the size of Earth and resembled the Great Red Spot on Jupiter. 

These storms are not permanent features like the Great Red Spot, though. After only a few years, we observed Neptune again to find an anticyclonic storm which had winds moving backwards at high pressures happening every couple of years.

Cold temperatures at the highest layers in Neptune’s atmosphere also cause methane clouds to condense.

At the lower layers, scientists believe clouds made up of ammonium sulfide, hydrogen sulfide and water could exist. In other areas there could also be clouds of water-ice.

The giant planet’s atmosphere is dominated by ice but, its temperatures are also dictated in part by heating from within its core.

In fact, motion inside Neptune’s core heats the planet far more than the Sun’s rays. It majorly affects the temperature of the ‘stratosphere’ layer, as this layer’s temperature increases with altitude.

Other layers include, the ‘troposphere’ which lies on the surface. The temperature actually decreases as the altitude increases. Additionally, the planet’s surface pressure is thought to be the equivalent of the pressure at sea level on Earth.

The temperature at this point is also thought to be about 63.1 Kelvin or -346 Fahrenheit.

Another layer is the ‘thermosphere’. Here, pressure is much lower, and the outer edge of the atmosphere is called the ‘exosphere’.

Each layer has different pressure and temperatures which will depend on a variety of factors - although each one is still very, very cold!

Like other gas giants, Neptune still holds a lot of the atmosphere it had during its formation

So, the gas giant’s pressures and temperatures change at different altitudes. At the very top of the clouds, the temperature averages at 63.1 Kelvin or -346 Fahrenheit.

Neptune's atmosphere predominantly consists of hydrogen and helium, with smaller traces of methane. Other contributors to the giant planet’s atmosphere are water-ice, ammonia hydro sulfide and ammonia-ice.

These gasses are what contribute to the planet’s extraordinary blueish color. The methane reflects blueish colors because it absorbs red lights.

The planet could have up to a hundred times more ethyne, ethane and methane at its equator than it does at its poles. This can affect the temperature too.

Gordon Watts
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