We've been looking at the idea of an ocean beneath Pluto's icy surface for some time, including interesting work on the thermal evolution of the dwarf planet's ice shell from Guillaume Robuchon and Francis Nimmo (University of California at Santa Cruz). Back in 2011, The Case for Pluto's Ocean looked at their view that the stretching of Pluto's surface would have clear implications for an ocean kept warm by radioactive decay in the interior. Now Nimmo is back with a post-New Horizons analysis that also points to an ocean. The key here is Sputnik Planitia, forming part of the heart-shaped feature that was so distinctive during the flyby -- think of Sputnik Planitia as the heart's 'left ventricle.' The impact basin here is aligned almost exactly opposite from Charon. We learn in Nimmo's paper in Nature that there is only a 5 percent chance that the feature's alignment with Pluto's tidal axis is by coincidence. To Nimmo and colleagues, the alignment is a dead giveaway that extra mass in...

Let's circle back this morning to ring systems, which were the subject of Monday's post. In particular, I was interested in new work on the rings of Uranus, for Voyager data, newly analyzed, has revealed patterns that indicate the presence of small 'shepherding' moons. We've seen the same phenomenon at Saturn, but what similarities exist between the two ring systems also highlight their differences. The rings of Uranus -- and this holds for Neptune as well -- are much darker than the rings of Saturn, which are mostly made up of icy particles. Darker rings, so the thinking goes, are a likely indication of higher rock content. But why are these ring systems so different, and what produced them in the first place? We have another new paper on the outer systems' rings to throw into the mix from Ryuki Hyodo (Kobe University), working with co-authors at the Université Paris Diderot and Tokyo Institute of Technology. The team developed computer simulations to construct a plausible...

The ring system of Uranus was the second to be discovered in our Solar System. You would assume this came about because of Voyager, but the discovery was actually made in 1977 through ground-based observations involving occultations of distant stars. The rings of Uranus are narrow -- between 1 and 100 kilometers in width -- and many are eccentric. The fact that they are composed of dark particles makes detection and study particularly difficult. Image: Uranus is seen in this false-color view from NASA's Hubble Space Telescope from August 2003. The brightness of the planet's faint rings and dark moons has been enhanced for visibility. Credit: NASA/Erich Karkoschka (Univ. Arizona). Voyager 2’s flyby of the planet in January of 1986 gave us useful information about the rings’ structure, with three occultation experiments performed during the flyby. We learned that the moons Cordelia and Ophelia were helping to shape the eccentricity of some of the rings (deviations of tens to hundreds...

Witnessing Titan's ever-changing seasons has been a major payoff of the Cassini mission, whose end is now close enough (September, 2017) to cause us to reflect on its accomplishments. We now see winter settling in firmly in the southern hemisphere, along with a strong vortex now developing over the south pole. When Cassini arrived in 2004, we saw much the same thing, only in the northern hemisphere. Athena Coustenis (Observatoire de Paris) is presenting results on Titan's climate at the ongoing joint meeting of the American Astronomical Society's Division for Planetary Sciences and 11th European Planetary Science Congress. "Cassini's long mission and frequent visits to Titan have allowed us to observe the pattern of seasonal changes on Titan, in exquisite detail, for the first time," says Dr. Coustenis. "We arrived at the northern mid-winter and have now had the opportunity to monitor Titan's atmospheric response through two full seasons. Since the equinox, where both hemispheres...

Considering how long we've been thinking about a massive planet in the outer Solar System — and I'm going all the way back to Percival Lowell's Planet X here — the idea that we might find the hypothetical Planet Nine in just three years or so is a bit startling. But Caltech's Mike Brown and colleague Konstantin Batygin, who predicted the existence of the planet last January based on its effects on Kuiper Belt objects, are continuing to search the putative planet's likely orbital path, hoping for a hit within the next few years, a welcome discovery if it happens. The duo are working with graduate student Elizabeth Bailey, lead author of a new study being discussed at the American Astronomical Society's Division for Planetary Sciences meeting in Pasadena, which is occurring in conjunction with the European Planetary Science Congress. The new paper is all about angles and alignments, focusing on the fact that the relatively flat orbital plane of the planets is tilted about...

We're getting close on New Horizons data, all of which should be downlinked as of this weekend. Although that's a welcome marker, it hardly means the end of news from the doughty spacecraft. For one thing, we have years of analysis ahead of us as we bring the abundant data from the spacecraft's instrument packages into focus. For another, we're still in business out there in the Kuiper Belt, heading for that interesting object 2014 MU69. Who knows what will turn up at the latter, given our propensity to be surprised at every turn in interplanetary exploration, from Triton's volcanic plains to fabulously fractured Miranda. And, of course, Pluto and Charon themselves, which turned out to be so interesting that Alan Stern, principal investigator for New Horizons, is already talking about future missions there. But back to 2014 MU69, which has continued to be the subject of Hubble observations even as New Horizons homes in on the object. As this news release from the mission points out,...

Back in the days when I was reading Poul Anderson's The Snows of Ganymede and thought of the moons of Jupiter as icy wastelands, I never would have dreamed there could be an ocean below their surfaces. But now we have oceans proliferating. Ganymede's may contain more water than all Earth's oceans, while Callisto is also in the mix, and we've known about Europa for some time now. At Saturn, the case for an ocean inside Titan seems strong, while Enceladus continues to spark mission proposals to study its frequent geysers. If you're a Centauri Dreams regular, you know that we've talked about Pluto's oceanic possibilities for some time, now strengthened in new work from Brandon Johnson (Brown University). Johnson and colleagues have modeled an ocean layer on Pluto more than 100 kilometers thick, with a salt content more or less like that of the Dead Sea on Earth. Johnson focused on Sputnik Planum, the 900-kilometer basin that comprises part of the heart-shaped feature we all learned to...

The latest news from the Chandra X-Ray Observatory is that the spacecraft, 100 times more sensitive to X-ray sources than any previous X-ray telescope, has found that Pluto is emitting X-rays. This marks the first time we've detected X-rays from a Kuiper Belt object. In fact, until now, the previous most distant Solar System body with detected X-rays was Saturn. But four Chandra observing runs from early 2014 through the summer of 2015 have detected X-rays, in work on Pluto done in coordination with the the New Horizons effort. Carey Lisse (JHU/APL) led the Chandra observing runs, working with New Horizons co-investigator Ralph McNutt (also at JHU/APL). Says Lisse: "We've just detected, for the first time, X-rays coming from an object in our Kuiper Belt, and learned that Pluto is interacting with the solar wind in an unexpected and energetic fashion. We can expect other large Kuiper Belt objects to be doing the same." The New Horizons pass by Pluto/Charon in July of last year is a...

Deep space exploration brings a surprise with each new destination. New Horizons made the point over and over again, and today we get word of new work on one of the mission's discoveries, that dark red polar cap at the north of Pluto's large moon Charon. Will Grundy (Lowell Observatory) and colleagues are behind the study, which digs into the theory that methane from Pluto's atmosphere is trapped at Charon's north pole. In a new paper in Nature, Grundy and team have used New Horizons mission data in conjunction with their own modeling of the evolution of Charon's ice cap over the course of a Plutonian year to demonstrate that the model of trapped methane works. It involves the processing of methane into complex organic molecules called tholins. From the paper: The distribution of dark, reddish material around Charon's northern pole is notable for its generally symmetric distribution across longitudes and its gradual increase with latitude, although there are local irregularities...

Have a look at an image Cassini acquired on July 25 of this year during its T-121 flyby of Titan. Here we're dealing with a synthetic-aperture radar image, but one that has been cleaned up with a 'denoising' algorithm that produces clearer views. Because of its proximity to the Xanadu region, the mountainous terrain shown here has been named the 'Xanadu annex' by Cassini controllers. Both features block the formation of sand dunes, which are elsewhere ubiquitous around Titan's equator. As on Earth, Titan's dunes flow around the obstacles they meet. These are the first Cassini images of the Xanadu annex, which is now revealed to be made up of the same mountainous terrain seen in Xanadu itself. Referring to the first detection of Xanadu, which occurred in 1994 through Hubble Space Telescope observations, JPL's Mike Janssen, a member of the Cassini radar team, calls the annex 'an interesting puzzle,' adding: "This 'annex' looks quite similar to Xanadu using our radar, but there seems to...

Since I've just finished reading Stephen Baxter and Alastair Reynolds' The Medusa Chronicles, a great deal of the action of which takes place beneath the upper clouds of Jupiter, I'm finding the Juno mission more than a little fascinating. The novel shows us a Jupiter that is the habitat of a variety of dirigible-like lifeforms, along with the predators that make their life difficult, and a mysterious world far beneath that I won't spoil for you by describing. Juno is delving into mysteries of its own. The spacecraft's first images of Jupiter's north pole, taken on August 27, mark the first of 36 close passes that will define the mission. As is so often the case with first-time planetary discovery, we are seeing things we didn't expect. Scott Bolton (SwRI) is Juno principal investigator: "First glimpse of Jupiter's north pole, and it looks like nothing we have seen or imagined before. It's bluer in color up there than other parts of the planet, and there are a lot of storms. There is...

We’ve all come to terms with the fact that beyond the orbit of Neptune there exists a large number of objects. These trans-Neptunian objects (TNOs) substantially altered the almost sedate view of the Solar System that prevailed in the first half of the 20th Century, showing us that far from being a tame and orderly place of planets, asteroids and comets, we were in a system filled with material left over the the system’s formation. Tame and orderly became ragged and unkempt, and it was clear that the outer system was a place ripe for discovery. Pluto was the first TNO to be discovered, all the way back in 1930, but the modern era of trans-Neptunian objects began in 1992 with the discovery of (15760) 1992 QB, and we can now count over 1750 TNOs, as listed by the Minor Planet Center. Bear in mind that we can divide the entire space occupied by TNOs into several prominent divisions: the Kuiper Belt, the Oort Cloud, and the scattered disk, with a few outliers like Sedna causing...

It was in 2012 that Cassini data showed us the presence of the river system now called Vid Flumina, which empties into Titan's Ligeia Mare after a journey of more than 400 kilometers. Given surface temperatures on this largest of Saturn's moons, researchers assumed liquid methane would be the key player here. The question was whether the river -- and the eight canyons that branched off from it along its course -- were still filled with liquid or long dry. Now we have the answer, thanks to new work from Valerio Poggiali (La Sapienza University, Rome) and colleagues. Using radar signals bounced off Titan's surface in May of 2013, the researchers probed the deep gorges near Titan's north pole and were able to distinguish rocky material from smooth liquid. We're clearly looking at a surface that is actively eroding, one with striking comparisons to the landscapes of Utah and Arizona as well as the Nile River gorge. Key to the work here is the use of Cassini's radar as an altimeter,...

I suspect most scientists would like to have a moment like the one Stanton Peale, Patrick Cassen and Ray Reynolds experienced when Voyager flew past Io in 1979. How many of us get to see a major idea vindicated in such short order? It was on March 5 that Voyager 1 passed within 22,000 kilometers of Io. A scant three days before, Peale, Cassen and Reynolds had published their prediction that tidal forces should keep the moon's interior roiling, resulting in volcanic activity. Linda Morabito, on the Voyager navigation team, analyzed Voyager imagery shortly thereafter to discover that volcanoes were indeed active on the surface. What a triumph for the power of thorough analysis and prediction. Voyager, in fact, found nine plumes on Io, while demonstrating that its surface was dominated by sulfur and sulfur dioxide frost, with extensive lava fields extending for hundred of kilometers. The moon was also observed to have a thin atmosphere consisting primarily of sulfur dioxide. That thin...

Speculating about what an advanced extraterrestrial civilization might do has kept us occupied for the last two days, with gas giants like Jupiter the primary topic of conversation. We don't know if it's possible to ignite a gas giant to provide new sources of energy. But with Juno getting ready to measure Jupiter's aurorae, we're looking at naturally produced energy today, and now we have interesting work on the planet's Great Red Spot that comes out of Earth-based observations. The enormous storm turns out to be a key factor in heating Jupiter's atmosphere. And what a storm it is. We knew about the Great Red Spot as early as the 17th Century because its span -- three Earth diameters -- qualifies this highly visible maelstrom as the largest hurricane we know of. Winds can take six days to complete one circuit of the Great Red Spot, which has varied in size and color ever since it was discovered. It is now observed to span 22,000 km by 12,000 km in longitude and latitude,...

A dwarf planet designated 2015 RR245 (and now in search of a name) has been found in an orbit that takes it out to at least 120 AU. It's a discovery made by the Outer Solar System Origins Survey (OSSOS), an international collaboration focused on the Solar System beyond Neptune. The goal is to test models of how the Solar System developed by studying the movements of icy objects, many of which may have been destroyed or ejected from the Solar System altogether through movements of the giant planets early in the formation process. Image: Rendering of the orbit of RR245 (orange line). Objects as bright or brighter than RR245 are labeled. The blue circles show the projected orbits of the major planets. The Minor Planet Center describes the object as the 18th largest in the Kuiper Belt. Credit: Alex Parker/OSSOS team. We've had a close look at one dwarf planet at the edge of the system when New Horizons flew past Pluto a year ago, and with a diameter of roughly 700 kilometers, 2015 RR245...

We don't have high-resolution pictures of Jupiter from the Juno mission yet, but we do have JunoCam in operation. It's a color camera working in visible light that has returned data following the spacecraft's arrival at Jupiter on July 4. This JPL news release tells us that JunoCam was folded into the mission as part of NASA's public outreach. It is not, in other words, considered a science instrument, and we'll need to wait until late August for the first high-resolution images. Still, it's satisfying to see that all is apparently well in Jupiter space. Image: This color view from NASA's Juno spacecraft is made from some of the first images taken by JunoCam after the spacecraft entered orbit around Jupiter on July 5th (UTC). The view shows that JunoCam survived its first pass through Jupiter's extreme radiation environment, and is ready to collect images of the giant planet as Juno begins its mission. Credit: NASA/JPL-Caltech/SwRI/MSSS. Here we're about 4.3 million kilometers from...

If you're looking for liquid water on Titan, prepare to go deep, perhaps as much as 100 kilometers below the Saturnian moon's crust, which is itself made of ice. When it comes to exoplanets, we always talk about the habitable zone as a place where liquid water could exist on the surface. Titan clearly fails that test. But is it a place where life could exist anyway? A new paper gets us into this interesting topic by suggesting that prebiotic chemistry -- and possibly even biochemistry -- could take place on Titan. The work of Martin Rahm and Jonathan Lunine, working with colleagues David Usher and David Shalloway (all at Cornell University), the study sees Titan as a 'natural laboratory' for exploring non-terrestrial prebiotic chemistry given the presence of liquid hydrocarbons and the lack of liquid surface water. Image: An image of Titan's surface, as taken by the European Space Agency's Huygens probe as it plunged through the moon's thick, orange-brown atmosphere on Jan. 14, 2005....

A reminder of how challenging it is to operate with solar power beyond the inner system is the fact that Juno carries 18,698 individual solar cells. Because it is five times further from the Sun than the Earth, the sunlight that reaches Juno is 25 times less powerful, a reflection of the fact that the intensity of light is inversely proportional to the square of the distance from the source. In other words, if you're going to use solar power this far out from the Sun, you'd better have plenty of surface area. Juno carries three 9-meter solar arrays that could, at Earth's distance of 1 AU, generate as much as 14 kilowatts of electricity. But at Jupiter's distance, controllers are expecting a realistic output of about 500 watts. Making solar power operations possible here is improved solar cell performance and a mission plan that avoids Jupiter's shadow. Image: This is the final view taken by the JunoCam instrument on NASA's Juno spacecraft before Juno's instruments were powered down...

People in the space business always joke about the stress levels at any launch, but if you're keeping tabs on a billion dollar spacecraft like Juno, I'd say the arrival can create just as many, if not more, gray hairs. Plenty of people are breathing easier this morning after Juno's successful 35-minute engine burn and entry into orbit around Jupiter, confirmation of which came in just before midnight Eastern US time (03:53 UTC on July 5). Congratulations to the entire team. All of this was part of a sequence of arrival events -- Juno's orbit-insertion phase (JOI) -- that included spinning up the spacecraft from 2 to 5 revolutions per minute as an aid to stability, along with attitude changes in anticipation of the main engine burn, which began at 23:18 EDT. The latter decreased the spacecraft's velocity by 542 meters per second to make orbital capture possible. Juno has already been turned again to allow its solar cells to work at full capacity. Image: The Juno team celebrates at...