What Is The Surface of Neptune Like?

Neptune Hurricanes

As a gas giant (or ice giant), Neptune has no solid surface. In fact, the blue-green disc we have all seen in photographs over the years is actually a bit of an illusion. What we see is actually the tops of some very deep gas clouds, which in turn give way to water and other melted ices that lie over an approximately Earth-size core made of silicate rock and a nickel-iron mix. If a person were to attempt to stand on Neptune, they would sink through the gaseous layers.

As they descended, they would experience increased temperatures and pressures until they finally touched down on the solid core itself. That being said, Neptune does have a surface of sorts, (as with the other gas and ice giants) which is defined by astronomers as being the point in the atmosphere where the pressure reaches one bar. Because of this, Neptune’s surface is one of the most active and dynamic places in entire the Solar System.

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Exosphere

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The Earth’s atmosphere is broken up into several distinct layers. We live down in the troposphere, where the atmosphere is thickest. Above that is the stratosphere, then there’s the mesosphere, thermosphere and finally the exosphere. The top of the exosphere marks the line between the Earth’s atmosphere and interplanetary space.

The exosphere is the outermost layer of the Earth’s atmosphere. It starts at an altitude of about 500 km and goes out to about 10,000 km. Within this region particles of atmosphere can travel for hundreds of kilometers in a ballistic trajectory before bumping into any other particles of the atmosphere. Particles escape out of the exosphere into deep space.

The lower boundary of the exosphere, where it interacts with the thermosphere is called the thermopause. It starts at an altitude of about 250-500 km, but its height depends on the amount of solar activity. Below the thermopause, particles of the atmosphere have atomic collisions, like what you might find in a balloon. But above the thermopause, this switches over to purely ballistic collisions.

The theoretical top boundary of the exosphere is 190,000 km (half way to the Moon). This is the point at which the solar radiation coming from the Sun overcomes the Earth’s gravitational pull on the atmospheric particles. This has been detected to about 100,000 km from the surface of the Earth. Most scientists consider 10,000 km to be the official boundary between the Earth’s atmosphere and interplanetary space.

We have written several articles about the Earth’s atmosphere for Universe Today. Here’s an article about an evaporating extrasolar planet, and this article explains how far away space is.

You can learn more about the layers of the atmosphere, including the exosphere from this page at NASA.

We have recorded a whole episode of Astronomy Cast talking about the Earth’s (and it’s atmosphere). Check it out here, Episode 51: Earth.

Atmosphere Layers

Atmosphere layers. Image credit: NASA

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Seen from space, the Earth’s atmosphere is incredibly thin, like a slight haze around the planet. But the atmosphere has several different layers that scientists have identified; from the thick atmosphere that we breathe to the tenuous exosphere that extends out thousands of kilometers from the Earth. Let’s take a look at the different atmosphere layers.

Scientists have identified 5 distinct layers of the atmosphere, starting with the thickest near the surface, and then thinning out until it eventually merges with space.

The troposphere is the first layer above the surface of the Earth, and it contains 75% of the Earth’s atmosphere, and 99% of its water. Breathe in, that’s the troposphere. The average depth of the troposphere is about 17 km high. It gets deeper in the tropical regions, up to 20 km, and then shallower near the Earth’s poles – down to 7 km thick. Temperature and pressure are at the their highest at sea level, and then decrease with altitude. The troposphere is also where we experience weather.

The next atmosphere layer is the stratosphere, extending above the troposphere to an altitude of 51 km. Unlike the troposphere, temperature actually increases with height. Commercial airlines will typically fly in the stratosphere because it’s very stable; above weather, and allows them to optimize burning jet fuel. You might be surprised to know that bacterial life survives in the stratosphere.

Above that is the mesosphere, which starts at about 50-85 km above the Earth’s surface and extends up to an altitude of 80-90 km. Temperatures decrease the higher you go in the mesosphere, reaching a low of -100 °C, depending on the latitude and season.

Next comes the thermosphere. This region starts around 90 km above the Earth and goes up to about 320 and 380 km. The International Space Station orbits within the thermosphere. This is the region of the atmosphere where ultraviolet radiation causes ionization, and we can see auroras. Temperatures in the thermosphere can actually reach 2,500 °C; however, it wouldn’t feel warm because the atmosphere is so thin.

The 5th and final layer of the Earth’s atmosphere is the exosphere. This starts above the thermosphere and extends out for hundreds and even thousands of kilometers. Air molecules in this region can travel for hundreds of kilometers without bouncing into another particle.

We have written many articles about the Earth’s atmosphere for Universe Today. Here’s an article about the composition of the Earth’s atmosphere, and here’s information about the Earth’s early atmosphere.

Here’s a great article from NASA that explains the different layers of the atmosphere, and here’s more information from NOAA.

We have done a whole episode of Astronomy Cast just about Earth. Listen to it here, Episode 51 – Earth.