Aer

Aer depicts the Geocentric model, as shown by the sun not being the center of the system. The picture is a reference to terra, which had the 7 classical planets as the sublevels.
For each planet there is a Roman numeral next to it, which is the index for the letter to take from each planet's answers. The answer for 8th the Earth is the XORed answer of Terra thecathurtsme, as indicated by the 7 lines from the planets leading into it.
Doing so gives thornrar, which indicates that there is a thorn.rar. Inside is an aer.txt that just says:

stop using outdated models

Thus instead of the Geocentric model, switch to using the Heliocentric model, which changes the order of the first 5 letters from thorn to north.
Inside north.rar is aerQ.png, which shows half of a QRcode.

Aer has been solved, the next step is at Conclusion, Extra Terra, and more.