Answer Happy

Question 5 (10 marks) In this question we will investigate the planet Horus, introduced in the previous question. In the years since your discoveries in Question 1, the inhabitants of Anubis have developed space travel, and sent a space-probe to orbit Horus. This orbiter has mapped the surface, measured altitudes, and taken more detailed photographs of selected regions. Horus turns out to be a very grey spherical planet, of radius 2,400 km. It has an extremely thin nitrogen atmosphere, but no measurable magnetic field. The Deuterium-to-Hydrogen ratio in the atmosphere of Horus is 12 times higher than on Anubis (i.e. Horus has relatively more deuterium). The surface of Horus is divided into two quite different types of terrain. There are highlands, typically 2 km above the mean elevation, and lowland plains, typically around 2 km below the mean elevation. The boundaries between the highlands and lowlands are usually marked by dramatic cliffs: Around 80% of the planet is covered with the lowland plains, and 20% with the highlands.
Here is a typical image of part of a lowland plain (Location A in the map above): (Location A) Here is a typical image of part of the highlands (Location B): (Location B) Note - both images show the same size region of Horus's surface.
Some highland regions show strange surface markings. One example is Location C: (location C). Similar features are not seen in the lowland plains. The lowland plains are mostly flat, but in a few regions, chains of mountains are seen: (Chain of mountains seen in a lowland plain. Chain is around 400 km in length).
Your orbiter obtained near-IR spectra of several different regions. The highland and lowland regions have distinctively different spectra: Typical highland region (green) and lowland region (blue) reflectance spectra. Deduce as much as you can about Horus from these data. Clearly explain your reasoning.