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...

You get to expect the unexpected when writing about space probes, but somehow what New Horizons did to my weekend completely blind-sided me. Running a routine check of email before (I thought) sliding into the rest of a relaxing work break, I found messages about the glitch on the Pluto-bound spacecraft. Sunday turned into an all-screens-on exercise in checking multiple feeds and waiting for news. The problem with New Horizons brought to mind a short story I wrote many years ago about an unmanned probe sent to Epsilon Indi on a 90-year journey. The probe is within a month of encounter when all goes silent and Earth controllers can only wait to see what happens. The point of the story (it was called "Merchant Dying," published in Charlie Ryan's Aboriginal Science Fiction in the July/August 1987 issue) was that spacecraft going to another star are going to need autonomous repair capabilities we can only dream of today. New Horizons is a long way out, but we can still work with it...

With New Horizons scheduled for its flyby of Pluto/Charon in a matter of weeks and a Kuiper Belt extended mission to follow, it’s interesting to note a new paper on objects well beyond Pluto’s orbit. Lucie Jílková (Leiden Observatory) and colleagues address the problem of Sedna and recently discovered 2012VP113. The problem they present is that even at their closest approach to the Sun, these two objects are outside the Kuiper Belt, while their aphelion distances are too short for them to be considered members of the Oort Cloud. So where do Sedna and 2012VP113 belong in our taxonomy of the Solar System? Thirteen such objects have now been discovered, a group collectively referred to as Sednitos. These objects have orbital elements in common: A large semi-major axis (with perihelion beyond 30 AU and aphelion beyond 150 AU), a common orbital inclination, and a similar argument of perihelion. A common origin seems likely. Jílková’s team is interested in the possibility that Sedna and...

An abrupt change: I'm holding today's post (about halfway done, on a stellar flyby that may have produced Sedna and other such objects long in our system's past) to turn to New Horizons' latest imagery, which is provocative indeed. We'll cover the Sedna story tomorrow. What we have from New Horizons is the work of the spacecraft's Long Range Reconnaissance Imager (LORRI) in a series of images that show Pluto and its largest moon Charon as they more than double in size between May 29 and June 19. There's plenty here to marvel at, but what stands out for me is the mysterious dark region that NASA's latest release refers to as 'a kind of anti-polar cap' on Charon. Have a look: Image: These recent images show the discovery of significant surface details on Pluto's largest moon, Charon. They were taken by the New Horizons Long Range Reconnaissance Imager (LORRI) on June 18, 2015. The image on the left is the original image, displayed at four times the native LORRI image size. After...

It's hard to consider a place with surface temperatures of -180°C 'Earthlike,' but there are reasons why we see the term so often applied to Titan. The most striking of these is the presence of surface lakes and seas, a phenomenon found nowhere else in the Solar System. The temperatures are cold enough to make the circulating fluid liquid methane and ethane rather than water, but we see things in Cassini imagery that are strikingly familiar, including seas fed by river-like channels and large numbers of shallow lakes that appear in flatter areas. The European Space Agency's Thomas Cornet has been leading a team investigating Titan's surface features in greater detail. In particular, the lakes of Titan do not appear to be fed by rivers, making it likely that they are filled either by rainfall or by liquids welling up from below. Empty depressions can be found where lakes may once have been, and it is believed that some of the lakes dry out during Titan's thirty-year cycle of...

New imagery from New Horizons continues to dazzle, with the images below taken by the spacecraft's Long Range Reconnaissance Imager (LORRI) instrument from May 29 to June 2. We're beginning to pick up bright areas mixed with dark terrain in what are clearly the best images ever obtained of the remote world. As before, mission scientists are using deconvolution to sharpen the raw images and are also teasing out further details with contrast adjustments. The processing can produce artifacts so that fine details will have to be checked at closer range. Image: These images, taken by New Horizons' Long Range Reconnaissance Imager (LORRI), show four different "faces" of Pluto as it rotates about its axis with a period of 6.4 days. All the images have been rotated to align Pluto's rotational axis with the vertical direction (up-down) on the figure, as depicted schematically in the upper left. From left to right, the images were taken when Pluto's central longitude was 17, 63, 130, and 243...

I know I'm going to remember the summer of 2015 for a long time. The confluence of deep space missions has brought new images every week, including the latest view of Ceres and its enigmatic bright spots, which appears below. I'm already bracing myself for that Voyager-like sense of deflation once New Horizons gets past Pluto/Charon and the long-anticipated targets dwindle. Pluto has a special place for some of us because we grew up with it being considered the ninth planet. Dwarf planet or not, it's the final act of a classic Solar System tour. Not that we won't be returning to many of these places, but the timing is uncertain and once Juno finishes its work at Jupiter, we'll have no missions on their way to the outer planets. That makes this summer both energizing and a bit poignant, but let's enjoy it while we can. This view of Ceres, taken on June 6, really is spectacular. We're seeing the dwarf planet from 4400 kilometers as Dawn flies its second mapping orbit. The resolution is...

The image of Pluto on the right -- an artist's impression, to be sure (credit: NASA, ESA and G. Bacon, STScI) -- suggests Ganymede to me more than Pluto, but we'll have to wait and see what New Horizons turns up as it continues to close on its target. It's worth thinking about how our views of this place have changed over time. The world found by Clyde Tombaugh seemed small enough when he found it, but a fraction of its light was actually coming from its yet smaller moon, which wouldn't be discovered until USNO astronomer James Christy nailed it in 1978. Gregory Benford depicted Pluto with a nitrogen sea in a 2006 novel called The Sunborn, one in which he explored the possibility of life at -185 degrees Celsius, the lifeforms themselves the result of an experiment by heliopause beings who drew energy from magnetic interactions far from the Sun. Even more speculative is Stephen Baxter's story "Goose Summer" (from the Vacuum Diagrams collection of 2001), in which Plutonian life...

'Europa in a can' may be the clue to what's happening on Jupiter's most intriguing moon. Created by JPL's Kevin Hand and Robert Carlson, 'Europa in a can' is the nickname for a laboratory setup that mimics conditions on the surface of Europa. It's a micro-environment of extremes, as you would imagine. The temperature in the vacuum chamber is minus 173 degrees Celsius. Moreover, materials within are bombarded with an electron beam that simulates the effects of Jupiter's magnetic field. Ions and electrons strike Europa in a constant bath of radiation. What Hand and Carlson are trying to understand is the nature of the dark material that coats Europa's long fractures and much of the other terrain that is thought to be geologically young. The association with younger terrain would implicate materials that have welled up from within the moon, providing an interesting glimpse of what is assumed to be Europa's ocean. Previous studies have suggested that these discolorations could be...

We can hope that plumes like those found emanating from the south pole of Enceladus happen on other icy worlds. There have been hints of plumes at Europa but they've proven elusive to pin down. However, we're learning a great deal about the water inside Enceladus through Cassini flybys, using models based on mass spectrometry data the spacecraft has gained from the ice grains and gases in the moon's plumes. A similar approach on other icy moons, if possible, could save us from having to drill through kilometers of ice. What Christopher Glein (Carnegie Institution for Science) and team have done is to construct a chemical model that uses the Cassini observational data to determine the pH of the Enceladan ocean. It's an important reading because pH tells us how acidic the water is, which gives us a look into the geochemical processes occurring inside the moon. What the new work shows is that the plume is salty, with an alkaline pH of about 11 or 12. This Carnegie Institution news...

One of the more memorable moments from yesterday's teleconference on the New Horizons mission was Alan Stern's comment that the latest pixelated images of Pluto/Charon constituted his 'meet Pluto moment.' If anyone has an interest in meeting Pluto, it's Stern (Southwest Research Institute), who serves as principal investigator and whose unflagging efforts made it possible. As for those pixelated views, well, they're a glimpse of what is to come, but even now, they're telling us helpful things about the target. The animation below speaks volumes, with the first showing Charon's rotation with the center of Pluto fixed in the frame. The images were acquired with the Long Range Reconnaissance Imager (LORRI) camera. Image: A series of LORRI images of Pluto and Charon taken at 13 different times spanning 6.5 days, from April 12 to April 18, 2015. During that time, the spacecraft's distance from Pluto decreased from about 111 million kilometers to 104 million kilometers. Pluto and Charon...

What to make of the latest news about Ganymede, which seems to have a bulge of considerable size on its equator? William McKinnon (Washington University, St. Louis) and Paul Schenk (Lunar and Planetary Institute) have been examining old images of the Jovian moon taken by the Voyager spacecraft back in the 1970s, along with later imagery from the Galileo mission, in the process of global mapping. The duo discovered the striking feature that Schenk described on March 20 at the 46th Lunar and Planetary Science Conference in Texas. Says McKinnon: "We were basically very surprised. It's like looking at old art or an old sculpture. We looked at old images of Ganymede taken by the Voyager spacecraft in the 1970s that had been completely overlooked, an enormous ice plateau, hundreds of miles across and a couple miles high… It's like somebody came to you and said, 'I have found a thousand mile wide plateau in Australia that was six miles high.' You'd probably think they were out of...

An interesting model of planetary formation suggests that the architecture of our Solar System owes much to the effects of the giant planets as they migrated through the protoplanetary disk. Frédéric Masset (Universidad Nacional Autónoma de México) and colleagues go so far as to speculate that planetary embryos in orbits near Mars and the asteroid belt may have migrated outwards, depleting the region of materials that would become the cores of Jupiter and Saturn. The key is the heat an embryonic planet generates in the protoplanetary disk. Writing in Nature, the authors describe computations that model what happens to the rocky cores that will become gas giants. Tidal forces affecting planets in the protoplanetary disk have been thought to cause them to lose angular momentum, making their orbits gradually decay. The migration in this case should be inwards toward the star. But the researchers' model takes heat generated by material impacting onto the...

When it comes to Saturn, have you noticed what's been missing lately? Well, actually for the last two years. While the Cassini orbiter has had high-profile encounters with Titan, it has been in a high-inclination orbit that has meant no recent flybys of other Saturnian moons. All that has now changed as Cassini returned to the planet's equatorial plane this month, which means we can look forward to more interesting views like these mosaics of the planet's second largest moon Rhea. Image: Two mosaics of Saturn's icy moon Rhea, with constituent images taken about an hour and a half apart on February 9, 2015. Images taken using clear, green, infrared and ultraviolet spectral filters were combined to create these enhanced color views, which offer an expanded range of the colors visible to human eyes in order to highlight subtle color differences across Rhea's surface. The moon's surface is fairly uniform in natural color. Credit: JPL. The Rhea imagery comes from a flyby of the moon on...

You may be forgiven if you aren't familiar with the name Chariklo. Discovered in 1997, 10199 Chariklo is a 'centaur,' an outer system body with an orbit that moves between the orbits of Saturn and Uranus, just nudging the orbit of the latter. Its odd name (we're big on names and their derivations here) comes from a nymph who in Greek mythology was the wife of Chiron and daughter of Apollo. No centaur is larger than Chariklo (estimated diameter 250 kilometers), and until just the other day, no other centaur was known to have what Chariklo did: A system of rings. We've just learned, though, that the second largest centaur, 2060 Chiron, may have a set of rings of its own, although there are alternative ways of interpreting the data. Whether Chiron's rings are confirmed or not, what was once thought to be an unusual phenomenon, a feature of Saturn alone, is now turning out to be far more common, with rings known to orbit Jupiter, Uranus and Neptune as well as Chariklo. So we have...

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...