Cassini has shown us that the plumes of Enceladus are laden not just with ammonia and carbon dioxide but also traces of methane. Scientists at the University of Vienna (Austria) are not claiming this finding as evidence for life, but they have produced laboratory work showing that at least one kind of microbe could survive in conditions like those within the moon. Couple this with the presence of molecular hydrogen (H2), also found within the plumes, and the existence of microorganisms deep within Enceladus appears at least plausible. Some of the methane found in the Enceladus plumes may turn out to be produced by methanogens. The microorganism in question is Methanothermococcus okinawensis, which can be found around sea vents in the Okinawa Trough off Japan. In conditions like these, methanogenic archaea can sustain themselves by the chemical nutrients found around hydrothermal vents, a scenario that could likewise exist beneath the Enceladus ice. Simon Rittmann, working with...

With New Horizons in hibernation as it pushes on toward MU69, it's worth remembering how recently our knowledge of the Kuiper Belt has developed. Gerard Kuiper did not predict the belt's existence, though he did believe that small planets or comets should have formed in the region beyond the orbit of Neptune (he also thought they would have been cleared by gravitational interactions long ago). And I always like to mention Kenneth Edgeworth's work in a 1943 issue of the Journal of the British Astronomical Association, discussing the likelihood of small objects in the region. We could easily be calling the area the Edgeworth/Kuiper Belt, as I occasionally do in these pages. Which takes me back to the Voyager days. It wasn't until 1992 that astronomers discovered 15760 Albion, the first trans-Neptunian object detected after Pluto and Charon. Back in 1980, when controllers were deciding on adjustments to the trajectory of Voyager 1, Pluto was an option, as New Horizons PI Alan Stern has...

A Hubble project called Outer Planet Atmospheres Legacy (OPAL) has been producing long-term information about the four outer planets at ultraviolet wavelengths, a unique capability that has paid off in deepening our knowledge of Neptune. If you kept pace with Voyager 2 at Neptune, you'll recall that the spacecraft found huge dark storms in the planet's atmosphere. Neptune proved to be more atmospherically active than its distance from the Sun would have suggested, and Hubble found another two storms in the mid-1990's that later vanished. Image: Neptune's Great Dark Spot, a large anticyclonic storm similar to Jupiter's Great Red Spot, observed by NASA's Voyager 2 spacecraft in 1989. The image was shuttered 45 hours before closest approach at a distance of 2.8 million kilometers. The smallest structures that can be seen are of an order of 50 kilometers. The image shows feathery white clouds that overlie the boundary of the dark and light blue regions. Credit: NASA/JPL. Now we have...

New Horizons continues to push our limits, revealing new sights as it makes its way through the Kuiper Belt enroute to a January 1, 2019 encounter with the KBO 2014 MU69. No object this far from the Sun has ever been visited by a spacecraft. Adding further interest is the unusual nature of the target, for MU69 is thought to be a contact binary, two independent bodies that have touched (comet Churyumov-Gerasimenko is likely a contact binary as well). The beauty of this kind of exploration, of course, is that we so often get surprised when we reach our destination. Below is an image of NGC 3532, also known as the Wishing Well Cluster, an open cluster in the constellation Carina that has its own place in our observational history, becoming the first target ever observed by the Hubble Space Telescope. That was in May of 1990; this is New Horizons' view in December. The Wishing Well Cluster is a naked eye object for southern hemisphere observers, one of the most spectacular clusters of...

Icy moons around Jupiter and Saturn offer exciting venues for possible life elsewhere in our Solar System. But how do we penetrate surface ice to reach the oceans below? In today's post, Kostas Konstantinidis surveys the field of in-situ operations on places like Enceladus and Europa. Enceladus will be a tricky place to land thanks to rough topography and polar lighting conditions. Europa poses its own challenges; once we're down, how do we power up the technologies to get below the ice? Kostas developed a mission concept for DLR, the German space agency, to sample subsurface plume sources on Enceladus as part of the Enceladus Explorer (EnEx) project. He is currently working on a PhD thesis at Bundeswehr University (Munich) simulating a safe landing on that world, and tells me he hopes that by the end of his academic career, he will have 'a nice mugshot of an alien microbe swimming around in its natural environment to show for it.' How to get that mugshot is a fascinating issue, as...

What do asteroids 44 Nysa, 64 Angelina and the Galilean satellites Io, Europa and Ganymede have in common? They are all Solar System objects without an atmosphere that are highly reflective. They are also the subject of study in a new paper from Robert Nelson (Planetary Science Institute) that investigates a feature common to all: At small phase angles (the angle from the Sun to the target being observed), they show negatively polarized light. Light reflected from objects in the Solar System is usually polarized, meaning that the electric and magnetic vibrations of the electromagnetic wave occur in a single plane. The amount of polarization depends upon the reflective material, but also on the geometry, as a good astronomy textbook makes clear (I'm checking against Karttunen et al.'s Fundamental Astronomy, 6th ed., 2016). Image: The phases of Rhea. Emily Lakdawalla used these Cassini images to explain phase angle in a useful 2009 backgrounder. Her caption: The angle from the Sun, to...

Cassini's huge dataset will yield discoveries for many years, as witness the global topographical map of Titan that has been assembled by Cornell University astronomers. The map draws on topographical data of the moon from multiple sources by way of studying its terrain and the flow of its surface liquids. Bear in mind that only 9 percent of Titan has been observed at relatively high resolution, and another 25-30 percent at lower resolution. For the remainder, the team mapped the surface using an interpolation algorithm and a global minimization process described in the first of two papers in Geophysical Review Letters. The methods are complex and described in detail in the paper. For our purposes, let's look at the result: We present updated topographic and spherical harmonic maps of Titan making use of the complete Cassini RADAR data set for use by the scientific community. These maps improve on previous efforts (Lorenz et al., 2013; Mitri et al., 2014) through their increased...

Our continuing interest in Titan as a possible venue for life was energized last year with the publication of a paper by Martin Rahm and Jonathan Lunine, working with colleagues David Usher and David Shalloway (all at Cornell University). I've written about this one before (see Prebiotic Chemistry on Titan?) and won't revisit the details, but the gist is that hydrogen cyanide produced in Titan's atmosphere can condense into aerosols that are transformed into interesting polymers on the surface. Of these, the most intriguing seems to be polyimine. The authors see polyimine as capable of producing complex, ordered structures that absorb light, producing energy that can be used to catalyze prebiotic chemistry. Rather than looking in Titan's seas, the authors think we'll find hydrogen cyanide reactions in tidal pools on the shores near seas and lakes. It's an interesting proposition, and like so many notions about Titan, it requires us to get a payload back to the surface, as we did in...

We're getting interesting results from analysis of Juno's close flybys of Jupiter. The spacecraft has detected hydrogen, oxygen and sulfur ions moving at relativistic speeds in a new radiation zone just outside the atmosphere. We have its JEDI (Jupiter Energetic Particle Detector Instrument) to thank for the detection, which was made during approaches as close as 3400 kilometers from the cloud tops. Fast moving atoms without an electric charge -- energetic neutral atoms -- are thought to be the source of the new radiation zone as they move from gas around Io and Europa and become ionized in Jupiter's upper atmosphere. The new radiation zone is inside Jupiter's previously known radiation belts, which have also been under scrutiny by Juno. High-energy, heavy ions have been detected in the inner edges of the planet's electron radiation belt, previously thought to be made up primarily of electrons moving at near light speed. The heavy ions show up at high latitude locations within the...

Could plate tectonics occur on Europa? It's an intriguing notion because the surface crust of the Saturnian moon offers oxidants and other chemicals useful for life. The process called subduction, in which a tectonic plate slides underneath another plate and sinks, would offer a way for these materials to come into contact with the subsurface ocean. We would have, in other words, a first-class mechanism for feeding the ocean with nutrients. Image: Previous studies have hinted that something like subduction may have been happening on Jupiter's moon, Europa. A new study provides geophysical evidence that it could indeed be happening on the moon's icy shell. Credit: NASA/JPL-Caltech/SETI Institute. There has been earlier evidence of possible plate tectonic activity on Europa, based on studies of surface geology. In places, the icy crust seems to be expanding, and here we can draw an analogy with mid-ocean ridges on Earth, which spread as a result of tectonic activity. In our oceans,...

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...

Centauri Dreams returns with an essay by long-time contributor Alex Tolley. If we need to grow a much bigger economy to make starships possible one day, the best way to proceed should be through building an infrastructure starting in the inner Solar System and working outward. Alex digs into the issues here, starting with earlier conceptions of how it might be done, and the present understanding that artificial intelligence is moving at such a clip that it will affect all of our ventures as we transform into a truly space-faring species. Under the microscope here is a company called SpaceFab, as Alex explains below, and the potential of ISRU -- in situ resource utilization. Emerging out of all this is a new model for expansion. by Alex Tolley "Asteroid Facility" - Syd Mead To sail the heavens and reach the stars is extremely expensive.  With the technologies we can currently envisage, Earth's GDP will need to be orders of magnitude larger to support a starship program....

The paper in Nature covering an object known as 288P lays out the case in its title: “A Main Belt Comet.” But what makes this story stand out is the fact that 288P is also a binary. A team of scientists led by Jessica Agarwal (Max Planck Institute for Solar System Research) discovered when 288P neared perihelion in September of 2016 that it was not one but two objects, asteroids of roughly the same mass and size, in a binary separated by about 100 kilometers. Moreover, they have verified that the small system is not quiescent. Using the Hubble instrument, Agarwal and colleagues discovered that the increased solar heating due to perihelion was producing sublimation of water ice, in much the same way that the tail of a comet is created. Here’s how the paper describes the process on 288P: Repeated activity near perihelion is a strong indicator of the sublimation of water ice due to increased solar heating. A model of the motion of the dust under the influence of solar gravity and...

If New Horizons can make its flyby of Kuiper Belt Object MU69 at a scant 3500 kilometers, our imagery and other data should be much enhanced over the alternative 10,000 kilometer distance, one being kept in reserve in case pre-encounter observations indicate a substantial debris field or other problems close to the object. But both trajectories, according to principal investigator Alan Stern, have been moved closer following a ten-week study period, and both are closer than the 12,500 kilometers the spacecraft maintained in its flyby of Pluto. Image: Artist's concept of Kuiper Belt object 2014 MU69, which is the next flyby target for NASA's New Horizons mission. Scientists speculate that the Kuiper Belt object could be a single body (above) with a large chunk taken out of it, or two bodies that are close together or even touching. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker. Stern made the statement in early September at a...

One of the great values of the Kepler mission has been its ability to produce a statistical sample that we can use to analyze the distribution of planets. The population of asteroids in our own Solar System doubtless deserves the same treatment, given its importance in future asteroid mining as well as planetary protection. But when it comes to main belt asteroids, we're able to look up close, even though the number of actual missions thus far has been small. Thus it's heartening to see Pekka Janhunen (Finnish Meteorological Institute), long a champion of intriguing 'electric sail' concepts, looking into how we might produce just such an asteroid sampling through a fleet of small spacecraft. "Asteroids are very diverse and, to date, we've only seen a small number at close range. To understand them better, we need to study a large number in situ. The only way to do this affordably is by using small spacecraft," says Janhunen. The concept weds electric sails riding the solar wind with...

Image: A monitor shows the status of NASA's Deep Space Network as it receives data from the Cassini spacecraft, Friday, Sept. 15, 2017 in the Charles Elachi Mission Control Center in the Space Flight Operation Center at NASA's Jet Propulsion Laboratory in Pasadena, California. Credit: NASA/Joel Kowsky. Image: Cassini program manager at JPL, Earl Maize, center row, calls out the end of the Cassini mission. Credit: NASA/Joel Kowsky. Image: Cassini program manager at JPL, Earl Maize, left, and spacecraft operations team manager for the Cassini mission at Saturn, Julie Webster embrace after the Cassini spacecraft plunged into Saturn, Friday, Sept. 15, 2017 at NASA's Jet Propulsion Laboratory in Pasadena, California. At left is Cassini project scientist Linda Spilker. At right center is Jim Green, Director of NASA's Planetary Science Division. Credit: NASA/JPL-Caltech/Space Science Institute. Image: Saturn's active, ocean-bearing moon Enceladus sinks behind the giant planet in a farewell...