Some notes from yours truly:
- The drop off in number of missions between Mars and Jupiter and beyond speaks to the immense distance you must go to reach the gas giants. Distance is such a huge barrier in space exploration.
- Only nine missions to the Sun? Disappointing considering our huge gaps of knowledge in the inner workings of the solar cycle and solar flare triggers. I admit that getting closer may not yield more knowledge than distant optical measurements, but you never know until you're there. For example, Ulysses discovered the differences between solar min and max in the polar structure of the solar magnetic field by flying over the poles of the sun.
- One of the things that this diagram shows is the differences between how researchers make plots and how people of less expertise but more artistic talent make them. If I was to make a similar diagram, I would have plotted actual (or at least reasonable representations of) orbits, resulting in a much uglier but more accurate plot. While the picture created by the fine folks at NatGeo fails to portray a plethora of graphical facts, its power is in the simplicity and beauty of the information it does display. Sometimes it is difficult for an analytic mind to adopt a more aesthetic approach to graphics, even if it can improve the overall product.