The temperature of Earth’s atmosphere depends on which layer you’re in. Earth’s atmosphere is divided into five main layers: the troposphere, the stratosphere, the mesosphere, the thermosphere, and the exosphere (space).

If you measure temperature as you go up, the temperature kind of zig zags. The air starts off warm in the troposphere but gets colder as you go up, then warms again in the stratosphere. The mesosphere is the coldest layer, at -90 degrees Celsius; this is where meteors burn up. The thermosphere is probably the layer you’re asking about because it gets really hot, around 1500-1700 degrees Celsius. Interestingly, it doesn’t feel warm up there because it’s so close to being a complete vacuum. The reason this layer is so hot is because it absorbs a lot of energy from the sun, like x-rays and UV radiation, and converts it into heat. Also, since it’s so low pressure, the small number of gas particles it contains heat up very easily and quickly. These two factors together create the intensely hot temperature of the outer atmosphere.

The temperature of the entire atmosphere is not 1700°C, only the layer ( one of five which comprise the atmosphere) called the thermosphere. This is the officially the second-highest layer, but the layer beyond it ( the exosphere ) is so sparsely populated that it is essentially empty space (such that some scientists do not even consider it part of the atmosphere).

For the purposes of this question, consider the thermosphere to be the outer layer of the atmosphere. As the outermost layer, it is the first to be impacted by the high-energy radiation emitted by the sun. As these photons collide with particles in the thermosphere and transfer energy to the gases there, in some cases ionizing them and causing the auroras.

In addition, there aren't many particles there (even though it is denser than the exosphere, the pressure in the thermosphere is only a small fraction of that in the troposphere where humans live). This has the twofold effect of each particle taking in a lot of energy, and limiting the possibility of collisions with other particles to get rid of energy.

Interestingly, despite the temperature of the thermosphere being so high, it would feel quite cold and a typical thermometer would read below freezing. This is also a result of the low pressure: few particles means there would not be enough collisions to transfer a significant amount of energy (i.e., to cause a significant increase in temperature of the thermometer). Even though the temperature of the individual particles is very high, the total amount of heat contained is relatively low because of the low density. (This information is in the above references. For more, see the ScienceLine answers here. )

You did not specify which planet, moon, or star has an atmosphere with a temperature of 1700 degrees Celsius, so I can't answer as each atmosphere has its own reasons for having the temperature that it does.

If you are referring to Earth's atmosphere, thenthe answer is that Earth's atmosphere is not that hot. Earth's atmosphere ranges from about -50 Celsius to about 50 Celsius depending on season, time of day, and location. 1700 degrees Celsius is hot enough to melt most rocks. If Earth's atmosphere were to become that hot, then the entire planet would become one gigantic ocean of molten lava.

The temperature of the atmosphere on Earth is mostly between 0 degrees Celsius [freezing point of water = 32 deg F] and 40 degrees Celsius [104 degrees F]. The temperature of the atmosphere above Earth depends on the altitude [how high above earth the atmosphere is], and things like the weather at that altitude.

Wikipedia mentions that “Atmospheric temperature is a measure of temperature at different levels of the Earth's atmosphere. It is governed by many factors, including incoming solar radiation, humidity and altitude”. You can read more on the link below:

from Wikipedia