Q:  What happened to all the "cold Jupiters" ???


  A:  The "hot Jupiters" were discovered mostly by the transmit technique,
          which provides the SIZE of the planet (based on the amount of
          light that it blocks).  So, we know the radius of hot Jupiters,
          and can put them on this graph.

      But the "cold Jupiters", far from their stars, were discovered via
          the radial velocity technique.  It tells us the MASS of the planet
          (based on the motion it causes in its host star), but nothing
          about the size.  Without any information on the radius of the
          cold Jupiters, we can't put them on this graph.


      In other words, some techniques can tell us about a planet's
          SIZE, and others can tell us about its MASS -- but no 
          technique can do both.  So, depending on our method,
          we always gain only partial information.