Astronomical investigations can overlap in extremely helpful ways. Consider the Dark Energy Survey, which examines some 12 percent of the sky in an attempt to learn more about whatever force is accelerating the expansion of the universe. DES is trying to map hundreds of millions of galaxies and identify thousands of supernovae while looking for patterns in cosmic structure, using a 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory (Chile). What DES produces are thousands of images -- its initial search uncovered 1.1 billion candidate objects, most of which are galaxies or background stars. But among the objects are some that move in successive observations, the signature of objects in our Solar System. David Gerdes (University of Michigan) was able to find what appears to be a dwarf planet within the dataset. Called 2014 UZ224 and informally known as DeeDee (for Distant Dwarf), the object has now been characterized...

NASA is to discuss new findings about ocean worlds in our Solar System in a news conference at 1400 EDT (1800 UTC) on Thursday. The prospects for oceans in the outer system are surprisingly varied, ranging from the strong evidence of a subsurface, salty ocean on Europa to other Jovian moons like Ganymede and Callisto, and of course, Saturn's intriguing moon Enceladus. Titan is thought to have a salty ocean perhaps 50 kilometers below its ice shell, while there are also possible ocean venues on Mimas, Triton and even Pluto. The news briefing participants will be: Thomas Zurbuchen, associate administrator, Science Mission Directorate at NASA Headquarters in Washington Jim Green, director, Planetary Science Division at NASA Headquarters Mary Voytek, astrobiology senior scientist at NASA Headquarters Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California Hunter Waite, Cassini Ion and Neutral Mass Spectrometer (INMS) team lead at the Southwest...

The attitude you bring to a star field changes everything. When I was a kid trying to figure out how to use a small telescope, I scanned the usual suspects -- the Moon, Saturn and its rings, the Galilean satellites of Jupiter -- all the while planning to branch out into major wonders like M31 or the Ring Nebula in Lyra. But when I turned to deep sky objects, what I discovered was that I could see little more than faint smudges -- I was using no more than a 3-inch reflector. It was a disappointment for a while, until I accepted the limitations of my equipment. And then I became a cataloger of faint smudges, as avidly tracking down celestial objects as any stamp collector sorting through new finds. A patient uncle showed me how to look slightly away from the object I sought, to pick it up in peripheral vision. I began keeping notebooks listing my first glimpses of various nebulae and clusters. So many celestial objects were out of reach, but somehow a field of stars became wondrous not...

We’re getting a few clues about the nature of planet migration in the early Solar System thanks to a class of objects being described as ‘blue binaries.’ Cold Classical Kuiper Belt Objects (CCKBOs) are generally reddish, but a population of widely separated binaries has now been identified that is thought to have originated in the inner edges of the Kuiper Belt. The paper reporting on this work argues that these objects were pushed out a distance of over 4 AU to their present location among the CCKBOs as the result of gravitational interactions with Neptune billions of years ago, a movement induced by the migration of the planet from 20 to 30 AU. If so, we can draw some conclusions about that migration, and we’re reminded in the process of how rich the Kuiper Belt is in objects of different origins. Led by Wes Fraser (Queen’s University, Belfast), the study used data drawn from the Gemini North instrument and the Canada-France-Hawaii Telescope, both on Mauna Kea, as part of a project...

With my own memories of the July 4, 1997 landing of Mars Pathfinder at Chryse Planitia as fresh as yesterday, it's hard to believe that we are looking at the 20th anniversary of rover operations on the planet. But as the Curiosity rover continues its travels and we look toward the Mars 2020 rover mission, we're also taking a much longer look ahead at the worlds where life may be more likely to be found, the icy moons of Jupiter and Saturn. Ponder this: Testing at the Jet Propulsion Laboratory is showing that ice grains in conditions like we will encounter on places like Enceladus or Europa can behave like sand dunes. That means fine grains that could stall an improperly designed rover, leading NASA engineers to begin rethinking designs harking back to the early days of Moon exploration, lightweight commercial wheels attached to a flexible chassis, a system that has worked for a variety of missions but will need adjustment for future work. The rovers that use these systems will, in...

An obscure instrument called a blink comparator became world famous following Clyde Tombaugh's discovery of Pluto in 1930. It was by rapidly switching between astronomical photographs that the young Tombaugh was able to compare objects in the field of view where 'Planet X' was presumed to hide. Pluto turned out to be a good deal smaller than Percival Lowell had imagined, leading to thoughts of still more distant planets, but for a time the new planet was best known as a faint dot on a series of plates, moving against a fixed field of stars. Image: Clyde Tombaugh at the Blink Comparator five years after the Pluto discovery. Credit: Lowell Observatory Archives. All of this is wonderfully told in Michael Byers' 2010 novel Percival's Planet (Henry Holt and Co.), which draws on Tombaugh's story and depicts the entire Lowell Observatory scene in his time there (see A Tour de Force of Planetary Discovery for my review of the book). Or if you want the inside view, Tombaugh's own Out of the...

Earth's axial tilt (its obliquity) is 23.5 degrees, a significant fact for those of us who enjoy seasonal change. The 'tilt' is the angle between our planet's rotational axis and its orbital axis. If we look at Earth's obliquity over time, we find a 41,000 year cycle that oscillates between 22.1 and 24.5 degrees. Here the Moon becomes useful, with recent studies showing that without it, Earth's obliquity could vary by 25° (some earlier analyses took this number much higher). Now we have new data from the Dawn spacecraft at Ceres relating the dwarf planet's axial tilt to the locations where frozen water can be found on its surface. This is interesting stuff, because it depends upon the spacecraft's ability to measure the world it orbits. "We cannot directly observe the changes in Ceres' orientation over time, so we used the Dawn spacecraft's measurements of shape and gravity to precisely reconstruct what turned out to be a dynamic history," says Erwan Mazarico, a co-author of a...

With Cassini now in the final stages of its mission, we can look forward to just one more close flyby of Titan, the 127th targeted encounter, on April 22. 'Targeted' means that Cassini has to use its thrusters to position itself optimally for the flyby. The first of the images below, by contrast, comes from a 'non-targeted' flyby, one of several anticipated for 2017. The close pass will give researchers a chance to probe the moon's northern seas one last time, which may prove useful in the investigation of the transient features some have dubbed 'magic islands.' Even as these studies proceed, Cassini will also be using the Titan flyby to alter its course enroute to the series of plunges through the gap between Saturn and its innermost rings now being called the Cassini Grand Finale. The spacecraft will plunge into Saturn's atmosphere on September 15. Image: As it sped away from a relatively distant encounter with Titan on Feb. 17, 2017, NASA's Cassini spacecraft captured this mosaic...

We've looked recently at the possibility of cryovolcanism on Ceres with regard to the unusual feature called Ahuna Mons (see Ice Volcanoes on Ceres?). Now we have further evidence that outbursts of brine from beneath the surface have been occurring over long periods of time, and that some of these eruptions have been recent. The work comes out of analysis of data from the Dawn mission by scientists at the Max Planck Institute for Solar System Research (MPS), and moves the debate to the unusual crater called Occator. Image: This view of the whole Occator crater shows the brightly colored pit in its center and the cryovolcanic dome. The jagged mountains on the edge of the pit throw their shadows on parts of the pit. This image was taken from a distance of 1478 kilometers above the surface and has a resolution of 158 meters per pixel. NASA/JPL-Caltech/UCLA/MPS/DLR/IDA. Dawn's Low Altitude Mapping Orbit (December 2015 to September 2016) took the spacecraft to within 375 kilometers of the...

You wouldn't expect main belt asteroids to develop tails like comets -- their orbits are circular enough that they don't undergo the kind of temperature swings many comets experience in their plunge toward perihelion -- but we do have some twenty cases of asteroids that do exactly that. The photo below, showing imagery from the 10.4-meter Great Canary Telescope, gives us views of asteroid P/2016 G1, with a smudgy dust trail splayed out behind the object. Image: Asteroid P/2016 G1 at three different times in 2016: late April, late May and mid June. The arrow in the center panel points out an asymmetric feature that can be explained if the asteroid initially ejected material in a single direction, perhaps due to an impact. Credit: Fernando Moreno (Institute of Astrophysics of Andalusia, Spain). Moreno and team, who have specialized in the dust environment near main belt objects, have now uncovered another intriguing asteroid, this one with an even more curious tail. Asteroid P/2016 J1...

With an ocean containing twice as much water as Earth's oceans, Europa is a high-priority target for astrobiology. But the presence of water alone is not what gives the Jovian moon such interest. After all, we're learning that icy worlds beyond the snowline can feature oceans beneath the surface, and we're learning more all the time about oceans all the way into the Kuiper Belt, as the ongoing investigation into what lies beneath Pluto continues. But Europa, like Enceladus, offers us substantial water in direct contact with a rocky seafloor, and that's a telling circumstance. What excites astrobiologists is water in the presence of the organic compounds that can become components of biology. The third factor is energy, which Europa has in abundance thanks to the tidal pull of Jupiter, causing flexing of the seafloor that may well be driving hydrothermal activity. Chemical compounds produced from interactions with Jupiter's magnetic field may also be useful as an energy source. In...

I don't want to get much deeper into February without looking at the recent Cassini imagery from Saturn's rings. Cassini, after all, is a precious resource, and every day that passes brings us closer to its mission-ending plunge into Saturn's cloud tops this September. Leading into that climactic event, however, we have the current ring-grazing orbits, a mission segment that is about half completed. Mission's end gives us the chance to see the rings in exquisite detail. 20 orbits are involved in the ring-grazing phase, each diving past the outer edge of the main ring system, before things get even more dramatic, and the so-called 'grand finale' begins. The latter is to include 22 orbits that will take Cassini through the gap between the rings and Saturn itself, with the first plunge scheduled for April 26. The payoff is immense: We've never had views as close or as dramatic of small moons like Daphnis, seen in the image below. Image: The wavemaker moon, Daphnis, is featured in this...

If a terrestrial volcano erupts in molten rock, an ice volcano in the outer Solar System would presumably erupt with volatiles like water or ammonia. We have evidence of such things in places like Pluto and Triton, far beyond the snowline where water is abundant. Some scientists think Quaoar may have had cryovolcanic activity, and other candidates include Titan, Europa and Miranda. Which brings us to Ahuna Mons on the dwarf planet Ceres. Discovered by the Dawn spacecraft in 2015, Ahuna Mons is unusual in many respects. Its sides are steep, its features well-defined, which suggests it is geologically young. If it is a cryovolcano, it seems to exist in splendid isolation, half the height of Mt. Everest on a surface otherwise bereft of similar features. Moreover, the orbit of Ceres between Mars and Jupiter gives us potential cryovolcanism closer to the Sun than has ever been observed before. Image: Ahuna Mons seen in a simulated perspective view. The elevation has been exaggerated by a...

The Japanese PROCYON spacecraft (Proximate Object Close flyby with Optical Navigation) has just given us an interesting case of repurposing a scientific instrument, not to mention drawing value out of a mission whose initial plans had gone awry. Launched together with JAXA's Hayabusa 2 probe in late December of 2014, PROCYON was to have flown by asteroid 2000 DP107 in 2016, but a malfunctioning ion thruster put an end to that plan. Fortunately, PROCYON carried LAICA, a telescope that was put to use to study the Earth's geocorona (the outermost layer of the atmosphere). Developed at Japan's Rikkyo University, LAICA observes emissions from hydrogen atoms, a useful capability when turned to comet studies, as a team of researchers has now done with comet 67P/Churyumov-Gerasimenko. Water being the most abundant cometary ice, its release rate helps map activity on the comet and offers clues to how water was incorporated into comets in the early Solar System. Image: The PROCYON spacecraft...

It doesn't stretch credulity to hypothesize that the early Earth benefited from an influx of comet and asteroid material that contributed water and organic compounds to its composition. The surface of a world can clearly be affected by materials from other bodies in the Solar System. Now we're learning that the dwarf planet Ceres may have a surface dusted by material from asteroid impacts. The findings come from a team of astronomers investigating Ceres with SOFIA, the airborne Stratospheric Observatory for Infrared Astronomy. The observatory is a highly modified 747SP aircraft carrying a 2.5m reflecting telescope. The study shows that not just Ceres but other asteroids and dwarf planets may be coated with asteroid fragments, a result that adjusts our view of Ceres' surface composition. After all, what we're looking at may simply be the result of asteroid impacts in the early days of the Solar System's formation. Three quarters of all asteroids, including Ceres, have been classified...

Have a look at Jupiter as seen by the Juno spacecraft on its third close pass. A view as complex as the one below reminds us how images can be manipulated to bring out detail. This happens so frequently in astronomical images that it's easy to forget this view is not necessarily what the human eye would see, and we always have to check to find out how a given image was processed. In this case, we're looking at the work of a 'citizen scientist,' one Eric Jorgensen, who enhanced a JunoCam image to highlight the cloud movement. Image: This amateur-processed image was taken on Dec. 11, 2016, at 1227 EST (1727 UTC), as NASA's Juno spacecraft performed its third close flyby of Jupiter. At the time the image was taken, the spacecraft was about 24,400 kilometers from the gas giant planet. Credit: NASA/JPL-Caltech/SwRI/MSSS/Eric Jorgensen. The image shows a region of Jupiter southeast of what is known as the 'pearl,' one of eight rotating storms at 40 degrees south latitude on the planet, a...

We've retrieved all the data from New Horizons' flyby of Pluto/Charon in 2015, the last of it being acquired on October 25 of this year. But data analysis is a long and fascinating process, with papers emerging in the journals and new discoveries peppering their pages. The New Horizons science team submitted almost 50 scientific papers in 2016, and we can expect that stream of publication to continue in high gear as we move deeper into the Kuiper Belt. For New Horizons is very much an ongoing enterprise, as Alan Stern's latest PI's Perspective makes clear. We have an encounter with a small Kuiper Belt object (KBO) called 2014 MU69 to think about, and the symmetry that Stern points to in his essay is striking. Two years ago New Horizons had just emerged from cruise hibernation as preparations for the Pluto/Charon encounter began. And exactly two years from now, we'll be again following the incoming datastream as the last of the New Horizons targets comes into breathtaking proximity....

Ceres, that interesting dwarf planet in the asteroid belt, is confirmed to be just as icy as we had assumed. In fact, a new study of the world, led by Thomas Prettyman (Planetary Science Institute), was the subject of a press conference yesterday at the American Geophysical Union fall meeting in San Francisco. Prettyman and team used data from the Dawn spacecraft's Gamma Ray and Neutron Detector (GRaND) instrument to measure the concentrations of iron, hydrogen and potassium in the uppermost meter of Ceres' surface. Prettyman, who is principal investigator on GRaND, oversees an instrument that works by measuring the number and energy of gamma rays and neutrons coming from Ceres. The neutrons are the result of galactic cosmic rays interacting with the surface, some of them being absorbed while others escape. The number and kind of these interactions allows researchers to investigate surface composition. Hydrogen on Ceres is thought to be in the form of frozen water, allowing the...

One of the great pleasures of doing this site is watching researchers matching ideas in peer-reviewed papers. A paper can meet the highest standards for publication but still present an argument that subsequent researchers question, igniting a new round of debate. Trying to get at the heart of a scientific question requires patience, but it's also as absorbing as a chess game, as witness the continuing debate over the history and significance of Pluto's Sputnik Planitia. And in this case, we have a researcher working both sides of the controversy. Resembling a polar ice cap, Sputnik Planitia is about 1000 kilometers across, and is centered on a latitude of 25 degrees north and a longitude of 175 degrees. Moreover, it is directly opposite the side of Pluto that always faces Charon, the result of tidal lock. Two weeks ago we looked at the possibility that this western lobe of Pluto's 'heart,' a deep basin filled with frozen gases like nitrogen, carbon dioxide and methane, was the...

What the Jet Propulsion Laboratory refers to as 'the first phase of the mission's dramatic endgame' begins tomorrow for the Cassini Saturn orbiter. Having given us an ocean within Enceladus and numerous images of Titan's lakes and seas (not to mention ring imagery of spectacular beauty), Cassini now enters a phase in which it encounters the rings in a new way, diving past their outer edge every seven days in a series of 20 passes. The spacecraft will be in an elliptical orbit inclined some 60 degrees from the planet's ring plane. "We're calling this phase of the mission Cassini's Ring-Grazing Orbits, because we'll be skimming past the outer edge of the rings," said Linda Spilker, Cassini project scientist (JPL). "In addition, we have two instruments that can sample particles and gases as we cross the ring plane, so in a sense Cassini is also 'grazing' on the rings." Image: Cassini crosses Saturn's F ring once on each of its 20 Ring-Grazing Orbits, shown here in tan and lasting from...