Seven years worth of Cassini images of Enceladus have told us what many have long suspected: The intriguing moon does indeed have a subsurface ocean. Not that the presence of water on Enceladus comes as a surprise: The south polar region in the area of the famous 'tiger stripes' has long been known to be venting vapor and liquid water from its fractures. The question had become, is this a regional body of water, or is the Enceladus ocean global? To find out, a team at Cornell University led by Peter Thomas, whose work was just published in Icarus, charted about 5800 surface features, contrasting images taken at different times and at different angles. Using a combination of dynamical modeling and statistical analysis, they sought to find the best values for the interior that would explain an apparent libration or 'wobble' (0.120 ± 0.014°) detectable in the imagery, a larger motion by far than would be expected if the surface of Enceladus were solidly connected with its...

Given the flow of new imagery from New Horizons, I began to realize that mission data were changing my prose. To be sure, I still lean to describing the system as Pluto/Charon, because given the relative size of the two bodies, this really seems like a binary object to me. I tend to call it a ‘binary planet’ among friends because I still think of Pluto as a planet, dwarf or not. But when New Horizons blew through the Pluto/Charon system, it was finally possible to start talking separately about Charon, because now we were seeing it, for the first time, up close. Charon as a distinct object from Pluto is a fascinating thought, one I’ve mused over since the days of the smaller object’s discovery in 1978. An enormous moon hanging in the sky, never changing its position, over a landscape unknown -- the imagination ran wild. In the event, New Horizons outdid anything I ever conceived, with imagery of both worlds we’ll be debating for a long time. But in some ways my favorite of the images...

Hard to believe it's been 55 days since the New Horizons flyby. When the event occurred, I was in my daughter's comfortable beach house working at a table in the living room, a laptop in front of me monitoring numerous feeds. My grandson, sitting to my right with his machine, was tracking social media on the event and downloading images. When I was Buzzy's age that day, Scott Carpenter's Mercury flight was in the works, and with all of Gemini and Apollo ahead, I remember the raw excitement as the space program kept pushing our limits. I had a sense of generational hand-off as I worked New Horizons with my similarly enthusiastic grandson. Carpenter took the second manned orbital flight in the Mercury program when Deke Slayton had to step down because of his heart condition, and the flight may be most remembered for the malfunction in Carpenter's pitch horizon scanner, leading to the astronaut's taking manual control of the reentry, which in turn led to overshooting the splashdown...

I'm really going to miss Cassini when it takes its plunge into Saturn's atmosphere in 2017. Having an orbiter in the outer system means that periodically we've been handed spectacular imagery and vast amounts of data for present and future analysis. Each new encounter now, such as the recent one with Dione, is a poignant reminder of how successful this mission has been, and how much we could gain with similar instrumentation around the ice giants. Meanwhile, I look at this striking view of Saturn and its rings from 20 degrees above the ring plane, a mosaic built from 75 exposures using Cassini's wide angle camera, and marvel at the view. The images were made in August of 2009, a day and a half after Saturn equinox, when the Sun was exactly overhead at the planet's equator. The result is a darkening of the rings from this perspective because of the Sun's lower angle to the ring plane, with shadows cast across the ring structure. It will be a while before we see this view again -- even...

At the Jet Propulsion Laboratory in Pasadena, Masahiro Ono has been using supercomputer simulations to model a new way of moving between small bodies in the Solar System. We've had a demonstration in the last few years of what ion propulsion can do to enable orbital operations at one asteroid (Vesta) followed by a journey to another (Ceres) and orbital insertion there. But Ono is looking at ways to simplify the process of asteroid and comet rendezvous that replaces the need for propellant during the orbital insertion and landing phases. Call it Comet Hitchhiker. "Hitchhiking a celestial body is not as simple as sticking out your thumb, because it flies at an astronomical speed and it won't stop to pick you up. Instead of a thumb, our idea is to use a harpoon and a tether," says Ono, who presents the idea today at the American Institute of Aeronautics and Astronautics SPACE conference in Pasadena. The work has intriguing implications for our investigations of the Kuiper Belt and outer...

What we'll eventually want is a good name. 2014 MU69 is the current designation for the Kuiper Belt Object now selected as the next destination for New Horizons, one of two identified as possibilities, and the one the New Horizons team itself recommended. Thus we have a target -- a billion and a half kilometers beyond Pluto/Charon -- for the much anticipated extended mission, but whether that mission will actually occur depends upon NASA review processes that are not yet complete. Still, the logic of putting the spacecraft to future use is hard to miss, as John Grunsfeld, chief of the agency's Science Mission Directorate, is the first to note: "Even as the New Horizon's spacecraft speeds away from Pluto out into the Kuiper Belt, and the data from the exciting encounter with this new world is being streamed back to Earth, we are looking outward to the next destination for this intrepid explorer. While discussions whether to approve this extended mission will take place in the larger...

As data return from New Horizons continues, we can hope that an encounter with a Kuiper Belt Object is still in its future. But such an encounter will, like the flyby of Pluto/Charon itself, be a fleeting event past an object at huge distance. Our next chance to study a KBO might take place a bit closer in, and perhaps we'll be able to study it with the same intense focus that Dawn is now giving the dwarf planet Ceres. How about an orbiter around Neptune, whose moon Triton is thought by many to be a KBO captured by the ice giant long ago? The thought is bubbling around some parts of NASA, and was voiced explicitly by the head of the agency's planetary science division, Jim Green, at this week's meeting of a working group devoted to missions to the outer planets. Stephen Clark tackles the story in Uranus, Neptune in NASA's Sights for a New Robotic Mission, which recounts the basic issues now in play. What comes across more than anything else is the timescale involved in putting...

The mapping of Ceres continues at a brisk pace. The Dawn spacecraft is now operating at 1470 kilometers from the surface, taking eleven days to capture and return images of the entire surface. As this JPL news release points out, each eleven day cycle consists of fourteen orbits, so we're accumulating views of this formerly faint speck in unprecedented detail. Within the next two months, Dawn will map Ceres -- all of Ceres -- six times. Have a look, for example, at this view of one of Ceres' more intriguing surface features. Taken by Dawn's framing camera on August 19, the image has a resolution of 140 meters per pixel. Image: NASA's Dawn spacecraft spotted this tall, conical mountain on Ceres from a distance of 1,470 kilometers. The mountain, located in the southern hemisphere, stands 6 kilometers high. Its perimeter is sharply defined, with almost no accumulated debris at the base of the brightly streaked slope. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA. The naming of surface...