Thermosphere

The air high up is very hot.

This layer sits far above the ground. It is near outer space. The sun sends energy to this part. This energy makes the air warm.

The air is very thin here. It is too thin for sound to travel. People do not live here. But space stations fly in this layer. They zoom around the Earth.

It is a very big place.

The thermosphere is a big layer of air high above Earth.

It starts about 80 km above the ground. This layer sits below the exosphere, which is the edge of space. The name comes from a Greek word for heat. This is because the air gets hotter as you go up.

Sunlight causes the heat. The sun sends out radiation, which is a type of energy. This radiation hits the gas in the thermosphere. It makes the gas particles become electrically charged. We call these charged particles ions. This creates the ionosphere. These ions help bounce radio waves back to Earth.

Even though it is hot, you would feel cold there. The air is very thin. There are not enough gas bits to move heat to you. This layer is also very quiet. The air is so thin that sound cannot travel through it.

Most people do not live here. But the International Space Station orbits in the middle of it. The Tiangong space station also flies in this layer.

The thermosphere is a huge layer of our atmosphere. It sits right above the mesosphere and below the exosphere.

This layer begins about 80 km above sea level. Its name comes from the Greek word "thermos," which means heat. Even though it is high up, it is a very important part of our world. It helps protect us by absorbing much of the sun's energy.

This layer works by absorbing energy from the sun. The sun sends out highly energetic radiation called X-rays and extreme ultraviolet radiation. When this radiation hits the gas in the thermosphere, it causes a process called photoionization. This means the particles become electrically charged, or they become ions. These ions create a region called the ionosphere. This ionosphere is very useful because it can refract radio waves. This allows radio signals to be received even beyond the horizon.

Scientists have studied how this layer changes over time. They know that temperatures in the thermosphere depend on solar activity. During quiet times, the temperature can be around 500 K. However, during busy solar periods, temperatures can rise much higher. The temperature at the very top can reach 1350 K.

This happens because the sun's radiation is very variable. Solar flares can increase the intensity of radiation by many orders of magnitude in just minutes.

There are many interesting facts about this high place. The thermosphere contains only 0.002% of the total mass of our atmosphere. Because the gas is so thin, it is almost a hard vacuum. This thinness means sound cannot travel through it.

You might also find a thick band of sodium here. This band has about 400,000 atoms per cubic centimeter. It stays there because meteors bring in more sodium as they fall. Astronomers even use this sodium to create "guide stars" for their telescopes.

Even though it is mostly empty, humans visit this layer. The International Space Station orbits in the middle of the thermosphere. It flies between 400 km and 600 km above Earth. The Tiangong space station also orbits in this same layer.

It is a place where technology and space meet. You can think of it as a bridge between our air and outer space. Most of the thermosphere is actually considered part of outer space.

The thermosphere is a massive layer of Earth's atmosphere. It sits directly above the mesosphere and below the exosphere.

This layer begins at an altitude of approximately 80 km (50 mi) above sea level. Its name comes from the Greek word "thermos," which means heat. While it is a part of our atmosphere, most of it is actually considered part of outer space. This is because the Kármán line, which marks the edge of space, is set at 100 km.

The thermosphere functions through the absorption of highly energetic solar radiation. The sun sends down X-rays and extreme ultraviolet (XUV) radiation. When these rays hit the gases in this layer, they cause photoionization or photodissociation. This process breaks molecules apart and creates ions, which are electrically charged particles. These ions form the bulk of the ionosphere.

This ionospheric region is very important for technology. It can refract radio waves, allowing signals to be received even beyond the horizon.

Temperature in the thermosphere behaves in a very unusual way. As you move higher into the layer, temperatures actually increase. This happens because the gases absorb intense solar radiation. However, an observer would not feel "hot" in the traditional sense. The gas density is extremely low, creating a state near a hard vacuum. Because there are so few molecules, they cannot conduct heat to an object. A thermometer would actually read significantly below 0°C, especially at night.

The composition of the gases also changes with altitude. In the lower atmosphere, turbulence keeps gases mixed. Above the turbopause, however, diffusive separation occurs. This means gases sort themselves by their molecular mass. Lighter elements like atomic oxygen (O), helium (He), and hydrogen (H) dominate at higher altitudes. There is also a thick band of elemental sodium at the edge of the mesosphere. This band contains about 400,000 atoms per cubic centimeter. It is constantly replenished by sodium sublimating from incoming meteors.

Solar activity plays a massive role in the energy budget of this layer. During quiet periods, solar XUV radiation provides about half of the energy input. This energy input is highest during the day at the equator. The temperature at the top of the layer, known as the exospheric temperature, varies greatly. It can range from about 740 K to 1350 K depending on the solar cycle. Solar flares can increase radiation intensity by many orders of magnitude in just minutes.

Other energy sources also heat the thermosphere. The solar wind transfers energy to the magnetosphere through various mechanisms. This can lead to Joule heating in the auroral regions. Additionally, atmospheric waves from the lower atmosphere move upward. Internal waves, such as gravity waves, transport energy upward until they dissipate. This dissipation contributes about 250 K to the heating of the thermosphere.

Despite its vast size, the thermosphere contains very little matter. It holds only about 0.002% of the total mass of Earth's atmosphere. Because the density is so low, the layer is an anacoustic zone. This means molecular interactions are too infrequent to allow sound to travel.

Humans do visit this layer, however. The International Space Station orbits in the middle of the thermosphere, between 400 km and 600 km. The Tiangong space station also orbits within this same region.