Until just a few years ago, a plot of mass versus size of other worlds would have looked pretty sparse and uninformative. But thanks to the tireless efforts of exoplanet astronomers, we now know fairly precise masses and radii for hundreds of distant worlds.
January 24 was the 30th anniversary of the Voyager flyby of Uranus. Uranian moons have been on my mind ever since New Horizons sent us close-up images of Charon. On the occasion of the anniversary, Ted Stryk produced latest-and-greatest versions of the Voyager views of these worlds.
How many planetary exploration missions are there, and where are they? These days, it's hard to keep track, because there are so many. I plan to begin the new year by taking stock of active missions, figuring out what each has set out to do and accomplished so far, but first I want to step back to consider the spread of missions across the solar system as a whole.
People often ask me to produce one of my scale-comparison montages featuring the small moons of the outer solar system. I'd love to do that, but Galileo's best images of Jupiter's ringmoons lack detail compared to Cassini's images from Saturn.