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...

We're in the immediate aftermath of Cassini's August 17 flyby of Saturn's moon Dione. The raw image below gives us not just Dione but a bit of Saturn's rings in the distance. As always, we'll have better images than these first, unprocessed arrivals, but let's use this new one to underscore the fact that this is Cassini's last close flyby of Dione. I'm always startled to realize that outside the space community, the public is largely unaware that Cassini's days are numbered. It's as if these images, once they began, would simply go on forever. The reality is that processes are already in place for Cassini's final act. The 'Grand Finale' will be the spacecraft's close pass by Titan (within 4000 kilometers of the cloud tops), followed by its fall into Saturn's atmosphere on September 15, 2017, a day that will surely be laden with a great deal of introspection. Bear in mind that not long after Cassini's demise, we'll also see the end of the Juno mission at Jupiter. We may still have our...

Looking for a good science fictional link to Saturn's moon Tethys (you'll see why in a moment), I came up short until I recalled Harry Bates' story 'A Matter of Size.' First appearing in the April, 1934 issue of Astounding Stories, the novelette tells the breathless tale of giant humanoid beings who live on Tethys, the descendants of a long lost Earth civilization, and their micro-scale counterparts, who keep science alive and kidnap earthmen to use as breeding stock. Poor Tethys, it deserves better at the hand of science fiction authors, though I do note that Healy and McComas incorporated the story in their Adventures in Time and Space (1946), and to be fair, its manic humor includes a sinister 'marriage machine,' surely a science fiction first, and a device calculated to strike terror in the hearts of young readers in Bates' era. If you know of more respectable appearances of Tethys in science fiction, let me know. Meanwhile, the actual moon is starting to get intriguing. Just...

The New Horizons imagery has been breathtaking, and never more so than in the image below. Here we're seeing Pluto seven hours after the July 14 closest approach, looking back at Pluto as it occults the Sun. The backlit atmosphere shows us layers of haze reaching 130 kilometers above the surface. Image: Pluto sends a breathtaking farewell to New Horizons. Backlit by the sun, Pluto's atmosphere rings its silhouette like a luminous halo in this image taken around midnight EDT on July 15. This global portrait of the atmosphere was captured when the spacecraft was about 2 million kilometers from Pluto and shows structures as small as 19 kilometers across. The image, delivered to Earth on July 23, is displayed with north at the top of the frame. Credit: NASA/JHUAPL/SwRI. Alan Stern, principal investigator for New Horizons, speaks of having his jaw on the ground when he saw our first image of an atmosphere in the Kuiper Belt, and for good reason. We've known that Pluto had some kind of...

We've already had the pleasure of naming features on Pluto, at least informally, highlighted by the moment when the heart-shaped area revealed by New Horizons was named Tombaugh Regio, after the world's discoverer. The fact that two of Clyde Tombaugh's children were in the audience during the news briefing where this occurred made it all the more powerful. Now we are turning to smaller features, as witness the mountain range near the southwest margin of Tombaugh Regio, viewed by New Horizons from a distance of 77,000 kilometers on July 20. Image: What a glorious view on what had previously been nothing more than a barely resolved dot. This is the region of Tombaugh Regio containing a range of mountains evidently less elevated than those previously seen near Pluto's equator (see First Post-Flyby Imager). Features as small as one kilometers across are visible in this image. Credit: NASA/JHUAPL/SWRI. The mountains in the equatorial region -- now known as Norgay Montes, after sherpa...

The latest view of Charon shows us a 390-kilometer strip of Pluto's largest moon with a unique feature, clearly visible below. We are looking at what Jeff Moore (leader of the New Horizons Geology, Geophysics and Imaging team, calls "a large mountain sitting in a moat." Moore is the first to admit that the scenario has geologists stumped. Image: This new image of an area on Pluto's largest moon Charon has a captivating feature -- a depression with a peak in the middle, shown here in the upper left corner of the inset. The image shows an area approximately 390 kilometers from top to bottom, including few visible craters. Credit: NASA-JHUAPL-SwRI. This view of Charon was taken at approximately 0630 EDT (1030 UTC) on July 14, 2015, about 1.5 hours before closest approach to Pluto, at a range of 79,000 kilometers. Again, notice the lack of craters here, reinforcing what we're learning about Charon's relatively young surface. I know we were all curious about Charon from the outset, but I...

Exoplanet hunter Greg Laughlin (UC-Santa Cruz), who could make a living as a poet (if it were possible to make a living as a poet) wrote recently of his hope for a Pluto image " that will become a touchstone, a visual shorthand for distance, isolation, frigidity and exile." We haven't seen that one yet, but I suspect we will with one of the images we're still to receive showing New Horizons' view of a receding crescent Pluto again being folded into the deep. Last night's reacquisition of the New Horizons' signal sets us up for many weeks of data return, and provides a triumphant exclamation point on the flyby. Our spacecraft punched right through the orbital plane of Pluto's system and emerged unscathed. The joy and festivity apparent on those actually at JHU/APL and the wild and celebratory conversations on social media bring home how popular this diminutive spacecraft has become. What an accomplishment, and even now I'm wondering what advances in technology could do in an outer...

Closest approach for New Horizons was at 0749:57 EDT (1149:57 UTC), with closest approach to Charon at about 0806 EDT. Mission operations manager Alice Bowman told the media briefing that we arrived at Pluto 72 seconds early and 70 kilometers closer than the aiming point, all of which was well within mission specs. Nice work. I've found Twitter the best place to keep up, along with NASA TV for the media briefings. The #PlutoFlyby hashtag has been so active that it's sometimes hard to read the messages, a heartening demonstration of the powerful sentiment this mission invokes. I also track @New Horizons2015, @NASANewHorizons, @AlanStern and, of course, @elakdawalla -- Emily Lakdawalla's work has been definitive. The Twitterverse has been exploding. And here is the latest image, showing 4 kilometers per pixel, about 1000 times higher than Hubble can provide. Much better still to come. Here we're sixteen hours from closest approach, at a distance of 766,000 kilometers. Note the varying...

We're under the 24 hour mark for the Pluto flyby. NASA will offer a news briefing for New Horizons (check NASA TV), covering mission status and what to expect during flyby, at 1030 EDT (1430 UTC) today, a schedule change that moves the time up by half an hour. On Tuesday morning, the agency will present a live program called Arrival at Pluto Countdown starting at 0730 (1130 UTC). Remember that closest approach to Pluto is scheduled to occur at approximately 0749 (1149 UTC) on Tuesday, when the spacecraft comes within 12,500 kilometers of the surface. Gathering data, the spacecraft will be out of communication for much of that day. Image: Pluto as seen from New Horizons on July 11, 2015. Credit: NASA/JHUAPL/SWRI You can check NASA's television coverage and media activities here, but I'll also send you to Emily Lakdawalla's page at The Planetary Society, where the indefatigable reporter has gathered in one place everything known about the schedule and other sources of information....

A chasm in Charon's southern hemisphere turns out to be longer and deeper than Earth's Grand Canyon, says William McKinnon (Washington University, St. Louis), deputy lead scientist with New Horizon's Geology and Geophysics investigation team. "This is the first clear evidence of faulting and surface disruption on Charon. New Horizons has transformed our view of this distant moon from a nearly featureless ball of ice to a world displaying all kinds of geologic activity." Image: Chasms, craters, and a dark north polar region are revealed in this image of Pluto's largest moon Charon taken by New Horizons on July 11, 2015. Credit: NASA/JHUAPL/SWRI. The most prominent crater, near Charon's south pole, is almost 100 kilometers across, and evidently the result of a geologically recent impact. This NASA news release adds that the darkness of the crater floor may be the result of a different kind of icy material being exposed, less reflective than the ices on the surface. Another possibility:...

The side of Pluto that always faces its large moon Charon is the side that New Horizons won't see when it makes its close flyby on July 14. That makes the image below what principal investigator Alan Stern is calling "the last, best look that anyone will have of Pluto's far side for decades to come." Image: New Horizons' last look at Pluto's Charon-facing hemisphere reveals intriguing geologic details that are of keen interest to mission scientists. This image, taken early the morning of July 11, 2015, shows newly-resolved linear features above the equatorial region that intersect, suggestive of polygonal shapes. This image was captured when the spacecraft was 2.5 million miles (4 million kilometers) from Pluto. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute. Four dark spots seem to be connected to the dark belt in Pluto's equatorial region, their fairly regular spacing a source of considerable curiosity. The large areas are estimated to...

Pluto's surface is beginning to be revealed, with the first signs of geological features, as principal investigator Alan Stern explains: "Among the structures tentatively identified in this new image are what appear to be polygonal features; a complex band of terrain stretching east-northeast across the planet, approximately 1,000 miles long; and a complex region where bright terrains meet the dark terrains of the whale. After nine and a half years in flight, Pluto is well worth the wait." Image: Tantalizing signs of geology on Pluto are revealed in this image from New Horizons taken on July 9, 2015 from 3.3 million miles (5.4 million kilometers) away. At this range, Pluto is beginning to reveal the first signs of discrete geologic features. This image views the side of Pluto that always faces its largest moon, Charon, and includes the so-called "tail" of the dark whale-shaped feature along its equator. (The immense, bright feature shaped like a heart had rotated from view when this...

New Horizons makes its closest approach to Pluto, at approximately 12,500 kilometers above the surface, at 0749 EDT (1149 UTC) on Tuesday July 14. Be aware that for much of that day, we'll be out of communication with the spacecraft while it's busy gathering data. About 2102 EDT (0102 UTC on the 15th), we should receive a confirmation of a successful flyby -- the spacecraft is scheduled to send a preprogrammed signal that it has survived the close approach. Then the data flow begins and will continue for months. NASA offers the schedule for the flyby here, with information on NASA TV coverage. We should be looking at close-up images of Pluto and hearing early reactions from the science team by mid-afternoon of Wednesday the 15th. And of course it will be possible to follow the mission on Facebook or on Twitter (also #PlutoFlyby). The nail-biting time will be the wait on the 14th for the signal announcing a successful transit of the system. It doesn't take a large object to silence a...