Saturn’s moon Enceladus transiting in front of its larger moon Rhea, as seen from a couple million miles away by the Cassini spacecraft, in photographs that span about one minute’s worth of time. That we can know to point cameras at this kind of event and get images this nice is a bit of a wonder to me.
NASA plans to send a hot-air-balloon type probe to Saturn’s moon, the only other known body in our solar system to have liquid “seas” on the surface. In order to keep the balloon from crashing into any rocky outcroppings, the team at the JPL has designed an oxygen-burning “rapid buoyancy modulation system” that’s pretty clever:
The lack of any free oxygen in the ice-moon’s air means that the patio gas oceans, clouds etc won’t normally catch fire. Thus NASA’s plan for Titanian hot-air ballooning would reverse the situation on Earth: Rather than burning a stream of patio-gas using oxygen in the air, the moon balloons will burn a stream of oxygen using methane from the surrounding clouds.