Region on the surface of Mercury of oddly rippled features. This feature is probably the result of a strong impact which occurred on the other side of the The term "planet" originally comes from the Greek word for "wanderer" since these objects were seen to move in the sky independently from the background of fixed stars that moved together through the seasons. The IAU last defined the term planet in 2006, however the new definition has remained controversial. Click on Term to Read More, and sent seismic waves traveling through and around the planet, converging in the weird region.
Image source: http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap08/FG08_25.jpg.