Yesterday's discussion of hydrothermal activity inside Saturn's moon Enceladus reminds us how much we can learn about what is inside an object by studying what is outside it. In Enceladus' case, Cassini's detection of tiny rock particles rich in silicon as the spacecraft arrived in the Saturnian system led to an investigation of how these grains were being produced inside Enceladus through interactions between water and minerals. If correctly interpreted, these data point to the first active hydrothermal system ever found beyond Earth. Now Ganymede swings into the spotlight, with work that is just as interesting. Joachim Saur and colleagues at the University of Cologne drew their data not from a spacecraft on the scene but from the Hubble Space Telescope, using Ganymede's own auroral activity as the investigative tool. Their work gives much greater credence to something that has been suspected since the 1970s: An ocean deep within the frozen crust of the moon. Image: NASA's Hubble...

Enceladus has been a magnet for investigation since 2005, when the Cassini spacecraft began to reveal the unusual activity at the moon's south pole, where we subsequently learned that geysers of water ice and vapor laden with salts and organic materials were spraying into space from deeply fractured terrain. Subsequent studies have homed in on what is now believed to be a 10-kilometer deep ocean beneath an ice shell 30 to 40 kilometers thick. Now we learn that evidence for hydrothermal activity -- water reacting with a rocky crust in a process that warms and saturates it with minerals -- has been found on Enceladus, drawing on a four-year analysis of Cassini data. The new paper, published in Nature, is one of two just out that paint a gripping picture of active processes on the moon. It uses computer simulations and laboratory experiments to make sense out of Cassini's early detection of silicon-rich rock particles flung into space by Enceladus' geysers. Researchers working on data...

Not long ago we looked at the discovery of what appears to be a disk orbiting the huge gas giant J1407b (see Enormous Ring System Hints of Exomoons). The example of Saturn is one thing that makes us wonder whether rings might exist around exoplanets, but of course in our own Solar System we also have Jupiter, Uranus and Neptune as hosts of ring systems of different sizes. In the case of J1407b, we’re not strictly sure that the object is a planet. If it’s actually a brown dwarf, we might be observing a protoplanetary disk in a young system. I’m not surprised when it comes to looking for ring systems around exoplanets that David Kipping (Harvard-Smithsonian Center for Astrophysics) should be in the mix. Working with Jorge Zuluaga (University of Antioquia) and two of their students, Kipping is co-author of a paper discussing how we might identify what are now being called ‘exorings.’ As illustrated in the figure below, an exoplanet’s transit signature is a key, taking advantage of the...

I spent the morning working on an interesting paper about detecting 'exorings' -- ring systems like Saturn's around exoplanets -- while switching back and forth to Twitter and various Web sources to follow events as the Dawn spacecraft became gravitationally captured by Ceres. I have problems with so-called 'multi-tasking,' which at least in my case means I do two things at once, performing each task less effectively than if I were tackling them separately. Fortunately, I have all weekend to tune up the exorings story, and I put it temporarily aside to work on Dawn's historic arrival. Congratulations to the entire Dawn team on the continuance of this splendid mission. We have much to look forward to as observations proceed and the orbit stabilizes. Similarly, we have the almost immediate prospect of following New Horizons in to Pluto/Charon, another case of a previously blurry object taking on breathtaking resolution as the days pass. The bounty of 2015 then opens into an uncertain...

Back in September of 1961, Isaac Asimov penned an essay in Fantasy & Science Fiction under the title "Not As We Know It," from which this startling passage: ...when we go out into space there may be more to meet us than we expect. I would look forward not only to our extra-terrestrial brothers who share life-as-we-know-it. I would hope also for an occasional cousin among the life-not-as-we-know-it possibilities. In fact, I think we ought to prefer our cousins. Competition may be keen, even overkeen, with our brothers, for we may well grasp at one another's planets; but there need only be friendship with our hot-world and cold-world cousins, for we dovetail neatly. Each stellar system might pleasantly support all the varieties, each on its own planet, and each planet useless to and undesired by any other variety. Asimov's idea, prompted by a monster movie excursion with his children, was to look at realistic ways that life much different from our own could emerge. Here he anticipated...

I'm interested in how we depict astronomical objects, a fascination dating back to a set of Mount Palomar photographs I bought at Adler Planetarium in Chicago when I was a boy. The prints were large and handsome, several of them finding a place on the walls of my room. I recall an image of Saturn that seemed glorious in those days before we actually had an orbiter around the place. The contrast between what we could see then and what we would soon see up close was exciting. I was convinced we were about to go to these worlds and learn their secrets. Then came Pioneer, and Voyager, and Cassini. And, of course, Dawn. As we discover more and more about Ceres, the process repeats itself, as it will again when New Horizons reaches Pluto/Charon. Below is a page from a book called Picture Atlas of Our Universe, published in 1980 by the National Geographic. Larry Klaes forwarded several early images last week as a reminder of previous depictions of the main belt's largest asteroid, or dwarf...

Approaching problems from new directions can be unusually productive, something I always think of in terms of Mason Peck's ideas on using Jupiter as a vast accelerator to drive a stream of micro-spacecraft (Sprites) on an interstellar mission. Now Peck, working with Robert Shepherd (both are at Cornell University) is proposing a new kind of rover, one ideally suited for Europa. The idea, up for consideration at the NASA Innovative Advanced Concepts (NIAC) program, is once again to exploit a natural phenomenon in place of a more conventional technology. What Peck and Shepherd have in mind is the use of 'soft robotics' -- autonomous machines made of low-stiffness polymers or other such material -- to exploit local energy beneath Europa's ice. We're at the edge of a new field here, with soft robotics advocates using principles imported from more conventional rigid robot designs to work with pliable materials in a wide range of applications, some of which tie in with the growth in 3D...

Have a look at the latest imagery from the New Horizons spacecraft to get an idea of how center of mass -- barycenter -- works in astronomy. When two objects orbit each other, the barycenter is the point where they are in balance. A planet orbiting a star may look as if it orbits without influencing the much larger object, but in actuality both bodies orbit around a point that is offset from the center of the larger body. A good thing, too, because this is one of the ways we can spot exoplanets, by the observed 'wobble' in the stars they orbit. The phenomenon is really evident in what the New Horizons team describes as the 'Pluto-Charon dance.' Here we have a case where the two objects are close enough in size -- unlike planet and star, or the Moon and the Earth -- so that the barycenter actually falls outside both of them. The time-lapse frames in the movie below show Pluto and Charon orbiting a barycenter above Pluto's surface, where Pluto and Charon's gravity effectively cancel...