Question: Just saw the stunning images of asteroid 2015 TB145. These are images obtained by illuminating the asteroid with microwaves from a source nearly the same direction as the receiving antenna. Why does the asteroid appear to be illuminated from the side, instead of directly from the front? – Steve
Answer: The light and dark areas on radar images of objects such as the asteroid 2015 TB145 are due to high and low reflectance of the radar signal off of the asteroid’s surface. For example, the brighter areas are places where the radar signal reflectance is higher than it is in the darker areas. This higher or lower reflectance can be due to ridges or other changes in the topography of the asteroid, or can also be due to changes in the roughness of the asteroid’s surface.