Several recent news items on Enceladus have me wanting to catch up with mission possibilities and the instruments that will drive them. NASA's thinking in that direction takes in a remote sensing instrument called SELFI, an acronym standing for Submillimeter Enceladus Life Fundamentals Instrument. The plan here is to examine the chemical composition of the plumes of water vapor and icy particles that are regularly lofted into space from Enceladus' south pole, in the region we've come to know as the 'tiger stripes.' Cassini data on the slight wobble in the orbital motion of Enceladus backs up the idea that the ocean beneath its ice is global, a body likely kept liquid by tidal energies as the moon is pulled and squeezed by Saturn in its orbit. The same process is likely the cause of the cracks that allow ocean water to escape into space, from perhaps as many as 100 sites on the surface. Image: The Cassini spacecraft detected hydrogen in the plume of gas and icy material spraying from...

The release of Cassini's last images of Saturn and its rings is a welcome event, a capstone to the mission that has taught us so much. What we see below is a series of images that have been grafted together, 42 red, green and blue images that allow us to see a wide-angle mosaic of Cassini's view. The images were taken by the spacecraft's wide-angle camera on September 13, and include the moons Prometheus, Pandora, Janus, Epimetheus, Mimas and Enceladus. Image: After more than 13 years at Saturn, and with its fate sealed, NASA's Cassini spacecraft bid farewell to the Saturnian system by firing the shutters of its wide-angle camera and capturing this last, full mosaic of Saturn and its rings two days before the spacecraft's dramatic plunge into the planet's atmosphere. During the observation, a total of 80 wide-angle images were acquired in just over two hours. This view is constructed from 42 of those wide-angle shots, taken using the red, green and blue spectral filters, combined and...

When I first wrote about the interstellar interloper now called 'Oumuamua, I made reference to Arthur C. Clarke's Rendezvous with Rama because of the delightful symmetry between the novel and the object, though noting that 'we're unlikely to find that A/2017 U1 is as intriguing as Clarke's mysterious starship bound for the Magellanics' (see An Interstellar Visitor?). Still, an interstellar object entering the Solar System only to go careening back out of it could not help but recall Clarke, whose 'asteroid' 31/439 wound up being artificial. Then came the paper from Karen Meech (University of Hawaii Institute for Astronomy, where the object was first detected with the Pan-STARRS1 telescope). Drawing on data from telescopes around the world, Meech's team has been able to characterize our first nearby object from another stellar system, with equally delightful results. For it turns out that 'Oumuamua (pronounced oh MOO-uh MOO-uh) has an unusual axis ratio, being about ten times longer...

Given yesterday's look at the ocean beneath Enceladus' ice, it seems the right time to examine the recent work on Ceres. We know that the dwarf planet may have had a global ocean of its own, but as with Enceladus, questions abound. Is there still liquid within Ceres? We have two new studies from the Dawn mission to give us some insights. The upshot: "More and more, we are learning that Ceres is a complex, dynamic world that may have hosted a lot of liquid water in the past, and may still have some underground," said Julie Castillo-Rogez, Dawn project scientist and co-author of the studies, based at NASA's Jet Propulsion Laboratory, Pasadena, California. Anton Ermakov (JPL) is lead author of the first paper, published in the Journal of Geophysical Research, which examined gravity data measurements from Dawn to analyze the composition of Ceres. This is exceedingly fine-grained work, drawing not only on Dawn data but on Deep Space Network observations of tiny changes in the spacecraft's...

How to explain the water vapor and ice blown off in the form of geyser-like jets from Enceladus? It’s a question we need to answer, because we’re learning just how interesting the icy moons of gas giants can be, with the potential for biological activity far from the Sun. In the case of Enceladus, though, the average global thickness of the ice is thought to be 20 to 25 kilometers. What has thinned the ice at the south pole, where warm fractures expel mineral-rich water into space? An unusual amount of heat is demanded to sustain this ongoing activity, along with a mechanism to explain what is happening within the moon. The heat in question is likely the result of friction, according to a new study published in Nature Astronomy. The work of Gaël Choblet (University of Nantes, France) and colleagues, the investigation involved modeling by Cassini researchers in Europe and the U.S., tapping the abundant data that the Saturn orbiter returned to Earth in its 13 years at the planet. It...