What is the Thermosphere

Although most people know that the earth is surrounded by layers of atmosphere that are conducive to the life forms that inhabit the earth, many have not heard of the layer known as the thermosphere. So what is the thermosphere and where is it?

The name thermosphere comes from the Greek words thermos, which means heat and sphere, which means globe. Located above the troposphere, the stratosphere and mesosphere is a layer of earth’s atmosphere known as the thermosphere. It is the layer just below the exosphere. The thermosphere layer is approximately 50 miles above the earth’s surface and can be anywhere from 291 miles to 384 miles thick. The thermosphere absorbs much of the X-ray and UV radiation from the sun so when the sun emits extreme radiation, as it does during solar flares, the thermosphere expands and begins to bulge. The lower altitudes of the thermosphere have relatively cooler temperatures than the upper altitudes because of this absorption of the sun’s radiation. The upper level of the thermosphere can reach temperatures of more than 3,000 degrees Fahrenheit in areas that face the sun and during solar flares temperatures can exceed 4,000 degrees Fahrenheit. The higher the thermosphere bulges, the more radiation it dissipates. This dissipation of the sun’s radiation helps to keep our planet at a temperature in which life on earth can exist in. Also because of the low density of the atomic makeup of the gases of the thermosphere, the atoms and molecules do not collide and transfer heat, so one would not feel the extreme heat that the sun’s radiation produces in the thermosphere. In fact, because the thermosphere is so near to the outer edge of our planet’s atmosphere and the vacuum of space, a thermometer would actually read temperatures well below zero.

The upper thermosphere contains gases that are made up of atoms and molecules of oxygen, nitrogen and helium, but the density of these atoms and molecules is very low. Because the air density in the thermosphere is very low, it is the ideal altitude for the space shuttle and International Space Station to establish orbit. However, the heating and expansion of the thermosphere creates some variance in the drag on these satellites, so they must continually have the altitude of their orbits adjusted.

The thermosphere’s atoms and molecules become electrically charged due to radiation from the sun and this charge can be used to bounce radio waves off the particles of the thermosphere. This makes it possible for radio waves to be received beyond line of sight or past the visible horizon.

These electrically charged atoms and molecules also discharge excess energy in one of the most dramatic and awesome displays known to man. As excess energy is discharged from these particles, they emit photons of light from the thermosphere. These light emissions are seen in near both the North Pole and the South Pole and are known as the Aurora Borealis or the Northern Lights. The undulations that are seen in the Aurora Borealis are caused by the waves of electrically neutral gases colliding with ions in motion within the earth’s atmosphere which affect the refraction of the light emitted by the photons as it leaves the higher altitudes of the thermosphere.

Should you be in an area where you can see the International Space Station pass overhead, you might be amazed to realize that you actually are looking at an object that is orbiting earth in the thermosphere layer. And should you be lucky enough to live in an area where you can observe the Aurora Borealis, you are looking at photons of light emitted from tiny atoms and molecules approximately 400 miles away from you in the thermosphere.