What is the solar system moon with the densest atmosphere? Most space fans know that the answer is Titan. A few of you might know that Triton's is the next densest. But what's the third? Fourth? Do any other moons even have atmospheres? In fact, they do; and one such atmosphere has just been discovered.
The road to lower costs outer planet missions has been paved by NASA’s first two New Frontiers missions, the $700M New Horizons mission to Pluto and the $1.1B Juno mission to Jupiter. But can the cost of a mission to the outer solar system be cut to $450M, the limit for a Discovery mission?
A newly published paper confirms a subsurface ocean at Ganymede. An ocean there was already suspected from its magnetic field and predicted by geophysics; new Hubble data confirms it, and even says it is in the same place we thought it was before. Such consistency is rare enough in planetary science to be worth celebration.
For the last two years, NASA has been the shy partner refusing to get on the dance floor, and Congress has been the aggressive partner insisting on a dance now. The dance is the continuing attempt by Congress to have NASA commit to a mission to explore Europa, and NASA’s attempts to delay a mission well into the 2020s.