Unusual Hollows Discovered on Planet Mercury . ... Credit Copyright: NASA / JHU APL / CIW Explanation: What are those unusual features on planet Mercury? The slightly bluish tinge of features dubbed hollows has been exaggerated on the above image by the robotic MESSENGER spacecraft currently orbiting Mercury . ... NASA's MESSENEGER is the first space spacecraft ever to orbit Mercury, and is currently scheduled to explore the Solar System's innermost planet into 2013. ... NASA Official: Jay Norris. ...