What is the density of the thermosphere?

Thermosphere is the layer of the atmosphere which is directly above the mesosphere and below exosphere .It extends from 90 km (56 miles) to 500 and 1,000 km (311 to 621 miles) above the earth.

~Hope this helps.

The internationally accepted start of outer space is 100km or the bottom levels of the thermosphere. The pressure is so low here that it is essentially a vacuum. The density, therefore is almost immeasurable since it is so low. As this part of the atmosphere is no longer homogeneous it is difficult to give an exact number, as particles are so far apart but also not uniformly separate. The best answer I can give is near zero.

The thermosphere is characterized by extremely low density. However, it is important to note that density in the thermosphere is highly variable and depends on factors such as solar activity and altitude. Generally, at its upper boundary, the density can be as low as 10^9 particles per cubic meter.