The small dot moving slightly off to the left of center in this image is newly-discovered Kuiper Belt object 2004 DW.
Date: 17 Feb 2004
2004 DW was found in images taken Feb 17, 2004 (nearly 74 years to the day after Pluto was discovered) by Mike Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale). They are the same people who found Quaoar in the summer of 2002.
2004 DW is one of the largest Kuiper Belt objects currently known. Initial indications are that it may be over half the diameter of Pluto, larger than Quaoar, and 2.4 billion kilometers (1.5 billion miles) further away than Pluto.
Read more about 2004 DW.
Image Credit: California Institute of Technology