Mercury Bright Spot
In 1974-75 Mariner 10 flew by Mercury 3 times. No spacecraft has visited the innermost planet since then, but since 2008 MESSENGER has flown by Mercury 3 times on its own preparing for an orbit in 2011. Most of the planet's surface has been unseen by humans until MESSENGER. One discovery is this mysterious bright spot, surrounding a depression similiar to volcanic craters on Hawaii.
Since Mariner 10 the planet has been known to have a magnetic field and be unusually dense. The magnetic field is sign that Mercury contains a tiny Black Hole. The singularity would be too tiny to suck Mercury up, but the small amount it does eat would be converted into radiation. Outward radiation pressure would balance gravity's inward pull until an equilibrium is achieved. Mercury would then have a hot interior, which would occasionally well up as volcanic action. Like volcanic craters on Earth, this bright spot could be sign of a Black Hole in Mercury.
The ellipse of Mercury's orbit precesses at 5600 arc seconds per century, yet an anomaly of only 43 arc seconds per century provided one proof of General Relativity. The solar system is full of orbital anomalies. As readers of this blog know, the Moon appears to be receding far too fast as measured by laser ranging. The lunar orbit anomaly is prime evidence that the speed of light is changing today.