The announcement that the Dawn spacecraft is running out of its hydrazine fuel was not unexpected, but when we prepare to lose communications with a trailblazing craft, the moment is always tinged with a bit of melancholy. Even so, the accomplishments of this mission in its 11 years of data gathering are phenomenal. They also speak to the virtues of extended missions, which in this case gave us views and a wealth of information about Vesta but also a continuation of its stunning orbital operations around Ceres. And at Ceres it will stay, a silent orbiting monument to deep space exploration. "Dawn's legacy is that it explored two of the last uncharted worlds in the inner Solar System," said Marc Rayman of NASA's Jet Propulsion Laboratory in Pasadena California, who serves as Dawn's mission director and chief engineer. "Dawn has shown us alien worlds that for two centuries were just pinpoints of light amidst the stars. And it has produced these richly detailed, intimate portraits and...

This morning we have an image of MU69, the Kuiper Belt object to which New Horizons is heading, with arrival and flyby scheduled for January 1, 2019. This just after the first glimpse of the asteroid Bennu by the spacecraft now heading there for observation and sample return, OSIRIS-REx. By way of comparison, the first glimpse New Horizons had of Pluto/Charon came during an optical navigation test using the Long Range Reconnaissance Imager (LORRI), which occurred in September of 2006 when Pluto was still 4.2 billion kilometers away. We knew in the year of its launch, in other words, that New Horizons could find and track targets at extremely long range, but MU69, otherwise known as Ultima Thule, is a tiny target indeed. Moreover, it's one that raises a host of obstacles particularly in terms of the background stars. We are trying to pluck it out of field objects from a distance of 172 million kilometers. "The image field is extremely rich with background stars, which makes it...

Meteorites have proven a useful tool for probing the nature of the early Solar System. Although I missed it at the time, Thomas Kruijer (University of Münster) and colleagues announced results last year from their study of the age of Jupiter based on measuring isotopes in meteorites. The age of Jupiter is an open question, but because current formation models have gas giants forming large solid cores and then rapidly accreting gas, the assumption is that the circumstellar disk could not have been depleted of its gas by the time Jupiter's formation was complete. A gas giant must form, in other words, fairly rapidly, and the Kruijer paper offered a deeper look into the conditions of the surrounding disk during the process. The researchers were able to identify "...two genetically distinct nebular reservoirs that coexisted and remained spatially separated between ~1 My and ~3-4 My after Solar System formation." Even that early in the formation of the Solar System, two bands of...

I am now back on the job, and somewhere beyond Pluto seems a good place to go. Somehow it seems safer out there. While vacationing here on Earth, I was bitten by a brown recluse spider, spent two weeks with a swollen and painful foot, and came down with the most intense flu-like symptoms I've ever experienced. The final indignity: I received my monthly report on Centauri Dreams reader statistics. Since I had done no posting for a large portion of this report, I was curious to find out how much traffic had slowed in my absence. It turned out that traffic increased right after I stopped posting and stayed robust the entire time. I am trying to figure out what this means... But back to New Horizons, putting my tumultuous vacation experience behind me. Anyone who remembers how hard it was to find a suitable Kuiper Belt Object to serve as New Horizons' next target will understand how challenging it would be to observe MU69 from the ground. The distant object, perhaps a binary, must be...

Something happens when we start making maps of hitherto unknown terrain. A sense of familiarity begins to settle in, a pre- and post-visit linearity, even when the landscape is billions of miles away. To put a name on a place and put that name on a map is a focusing that turns a bleary imagined place into a surface of mountains and valleys, a place that from now on will carry a human perspective. It can't be undone; a kind of wave function has already collapsed. And what place more remote than Pluto? At the dwarf planet's Tenzing Montes, we find striking peaks, some of them running up to 6 kilometers in height, and all this on a world that, until 2015, we weren't sure even had mountains. Certainly we weren't expecting mountains this tall, or a terrain this rugged. Given how many years may pass before we have another chance to visit Pluto/Charon, these first official validated topographic maps of the dwarf planet and its moon, just released, will carry our science -- and our...

It's startling to think that the Dawn spacecraft, now orbiting Ceres at its lowest altitude ever, may have fired its ion engine for the last time. The event occurred by way of positioning the spacecraft for the best possible track near Cerealia Facula, which is a prominent deposit of sodium carbonate in the center of the crater called Occator. Data from the spacecraft's visible and infrared imaging spectrometer had been used to identify the bright areas called faculae as calcium carbonate deposits earlier in the mission. Vinalia Faculae is in the same area. "Acquiring these spectacular pictures has been one of the greatest challenges in Dawn's extraordinary extraterrestrial expedition, and the results are better than we had ever hoped," said Dawn's chief engineer and project manager, Marc Rayman, of NASA's Jet Propulsion Laboratory, Pasadena, California. "Dawn is like a master artist, adding rich details to the otherworldly beauty in its intimate portrait of Ceres." Image: A...

Yesterday’s post about exoplanet obliquity inevitably brought our own system to mind, with the stark variations between planets like Earth (23 degrees), Uranus (98 degrees) and Mercury (0.03 degrees) serving as stark examples of how wide the variation can be. Thus seasonality has to be seen in context, and interesting questions arise about the effect of high degrees of obliquity on habitability. While thinking about that I received a new paper on Uranus that has bearing on the matter, with its attempt to quantify the ‘hit’ Uranus must once have taken. After all, something accounts for the fact that the 7th planet spins on its side, its axis at right angles to those of the other planets, its major moons all orbiting in the same plane. Lead author Jacob Kegerreis (Durham University), working with Luis Teodoro (BAERI/NASA Ames) and colleagues modeled 50 different impact simulations in an attempt to recreate the axial tilt of this world. In play were the planet’s internal structure,...

The quality of the image below isn't very high, but consider what we're looking at. This is the 'night side' of Pluto's moon Charon as viewed against a star field by the New Horizons spacecraft. We're looking at reflected light from Pluto --'Plutoshine' -- as the sole illumination of most of the surface. Who would have thought, in the 88 years since Clyde Tombaugh's discovery of Pluto, that we would see a Plutonian moon's dark side by Pluto's light? I wonder if there would have been a mission to Pluto at all if it hadn't been for James Christy. Working with astronomer Robert Harrington at the U.S. Naval Observatory Flagstaff Station (Arizona), Christy was situated just miles away from Lowell Observatory, where Pluto was discovered, when he noticed a strange elongation in images of the world. That was forty years ago, on June 22, 1978, during an effort to tighten up estimates of Pluto's orbit around the Sun. I suppose an astronomical analogue to this odd 'blob' on Christy's plates...

I set off an interesting conversation with a neighbor when organic material was detected on Ceres, as announced last year by scientists using data from the ongoing Dawn mission. To many people, 'organics' is a word synonymous with 'life,' which isn't the case, and straightening that matter out involved explaining that organics are carbon-based compounds that life can build on. But organic molecules can also emerge from completely non-biological processes. So with that caveat in mind about this word, it's still interesting that organics appear on Ceres, especially since water ice is common there, and we know of water's key role in living systems. A new paper looks again at data from Dawn, whose detections were made with infrared spectroscopy using its Visible and Infrared (VIR) Spectrometer. The instrument, examining which wavelengths are reflected off Ceres' surface and which are absorbed, detected organic molecules in the region dominated by Ernutet Crater on Ceres' northern...

I've always had a great interest in Iceland, stemming from my studies of Old Norse in graduate school, when we homed in on the sagas and immersed ourselves in a language that has changed surprisingly little for a thousand years. There's much modern vocabulary, of course, but the Icelandic of 1000 AD is much closer to the modern variant than Shakespeare's English is to our own. Syntactically and morphologically, Icelandic is a survivor, and a fascinating one. New Horizons' journey to Kuiper Belt Object MU69 occasions this reverie because the mission team has named the object Ultima Thule, following an online campaign seeking input from the public that produced 34,000 suggestions. The word 'thule' seems to derive from Greek, makes it into Latin, and appears in classical documents in association with the most distant northern areas then known. In the medieval era, Ultima Thule is occasionally mentioned in reference to Iceland, and sometimes to Greenland, and may have been applied even...

The longer we can keep a mission going in an exotic place, the better. Sometimes longevity is its own reward, as Curiosity has just reminded us on Mars. After all, it was only because the rover has been in place for six years that it was able to observe what scientists now think are seasonal variations in the methane in Mars' atmosphere. Thus the news that Juno will remain active in Jupiter space is heartening, and in this case necessary. The mission is now to operate until July of 2021, an additional 41 months in orbit having been approved. More time on station allows Juno to complete a primary science mission that had appeared in jeopardy. The reason: Problems with helium valves in the spacecraft's fuel system resulted in the decision to remain in the present 53-day orbit instead of the 14-day 'science orbit' originally planned, and that has extended the time needed for data collection. Thus the lengthening of operations there not only allows further time for discovery but...

Things always get interesting when the American Astronomical Society meets, which it is now doing in Denver, in sessions that will run until June 7. There should be no shortage of topics emerging from the meeting, but the first that caught my eye was a different approach to the putative world some are calling Planet Nine. Teasing out the existence of a planet at the outer edges of the Solar System has involved looking at gravitational interactions among objects that we do know about, and extrapolating the presence of a far more massive body. But the methodology may be flawed, if new work from Ann-Marie Madigan and colleagues at the University of Colorado Boulder is correct. At a press briefing at the AAS meeting, the team presented its view that objects like Sedna, an outlier that takes more than 11,000 years to complete an orbit around the Sun, should be considered in relation to other so-called 'detached bodies.' Almost 13 billion kilometers out, Sedna is one of a collection of...

I'm looking forward to the buildup as New Horizons gets ever closer to Kuiper Belt Object MU69 and whatever surprises will attend the flyby. But the ongoing operations of the Dawn spacecraft orbiting Ceres equally command the attention. The image below is one of the first images Dawn has returned in more than a year, a stark view of surface features taken on May 16 of this year. The altitude here is 440 kilometers -- for scale, the large crater near the horizon is about 35 kilometers wide. The foreground crater is about 120 kilometers from that crater, within a jumbled landscape suggestive of ancient terrain underlying the more recent impact. Image: On the way to its lowest-ever and final orbit, NASA's Dawn spacecraft is observing Ceres and returning new compositional data (infrared spectra) and images of the dwarf planet's surface, such as this dramatic image of Ceres' limb. Dawn has returned many limb images of Ceres in the course of its mission. These images offer complementary...

The ongoing work of mining New Horizons' abundant data from the outer system continues at a brisk pace. But missions occur in context, and we also have discoveries made at comet 67P/Churyumov-Gerasimenko by the European Space Agency's Rosetta probe to bring to bear. The question that occupies Christopher Glein and Hunter Waite (both at SwRI) is how to explain the chemistry New Horizons found at Pluto and what it can tell us about Pluto's formation. At the heart of their new paper in Icarus is the question of Pluto's molecular nitrogen (N2), which plays a role on that world similar to methane on Titan, water on Earth and CO2 on Mars. All are volatiles, meaning they can move between gaseous and condensed forms at the temperature of the planet in question. We've learned that solid N2 is the most abundant surface ice visible to spectroscopy on Pluto, as witness the spectacular example of Sputnik Planitia. Image: NASA's New Horizons spacecraft captured this image of Sputnik Planitia...

Once again we take advantage of older databanks to tease out new information. Europa is the case in point this morning, with Galileo data -- magnetic field and plasma wave observations from 1997 -- being brought in as evidence for a water vapor plume rising from the surface. The Galileo flyby took the craft closer than 400 kilometers, where a brief spike in plasma density was detected along with a concurrent decrease in magnetic field magnitude and a bend in the direction of the field. The data are consistent with a plume interacting with Jupiter’s plasma outflow, and support earlier Hubble indications of possible plumes on the moon. We have no firm measurement of the thickness of Europa’s ice, but if we are to get to that fascinating ocean now known to exist below the surface, we have to contend with penetrating it. Plumes from the interior would be helpful indeed, as Enceladus showed us at Saturn. Flying a spacecraft through a plume lets us measure its ingredients and sample the...

Our current depictions of conditions in the early Solar System involve titanic change, with the giant planets moving inward and then outward, creating gravitational havoc and scattering inner system objects in all directions. Such disruptions doubtless happen in other infant planetary systems and because of them, we can predict a large population of so-called ‘rogue’ planets that move through the galaxy dissociated from any star. Closer to home, there may well be small objects kicked into extreme orbits that bear evidence of these migrations. The ‘grand tack’ hypothesis sees Jupiter forming at around 3.5 AU, well in from its current 5.2 AU orbital position, with migration all the way in to 1.5 AU before a reversal of course and movement outward to its current position. Imagine Jupiter plowing through the asteroid belt -- twice -- and the chaos of its passage, producing a wide scattering in asteroid orbital inclinations and eccentricities. The ‘Nice model’ likewise involves gas giant...

The detection of hydrogen sulfide just above the upper cloud deck of Uranus has received the nods you might expect to rotten eggs, H2S having the odor of such unappetizing objects. But this corrosive, flammable gas is quite an interesting find even if it makes a whiff of Uranian air more off-putting than it already was. Not that you'd live long enough to notice the scent if you happened to be there, as Patrick Irwin (University of Oxford, UK) is quick to note: "If an unfortunate human were ever to descend through Uranus's clouds, they would be met with very unpleasant and odiferous conditions. Suffocation and exposure in the negative 200 degrees Celsius atmosphere made of mostly hydrogen, helium, and methane would take its toll long before the smell." We can leave that excruciating end to the imagination of science fiction writers, among whom I want to mention my two favorite stories about this planet, Geoff Landis' "Into the Blue Abyss" (2001) and Gerald Nordley's "Into the Miranda...

What would be our next step in the exploration of the outer system once New Horizons has visited one or more Kuiper Belt objects (KBOs)? One intriguing target with a nearby ice giant to recommend it is Triton, Neptune's unusual moon, which was imaged up close only once, by Voyager 2 in 1989. The views were spectacular but at the time of the encounter, most of Triton's northern hemisphere remained unseen because it was in darkness. Only one hemisphere showed up clearly as the spacecraft passed the moon at a distance of 40,000 kilometers. Our next visit should tell us much more, but we're still working out the concept. Thus Steven Oleson's Phase II grant from NASA's Innovative Advanced Concepts (NIAC) office. Oleson (NASA GRC) calls the idea Triton Hopper. In his Phase I study, he identified the various risks of the mission, analyzing its performance and its ability to collect propellant. For Triton Hopper -- moving from point to point -- would rely on a radioisotope engine that would...

Ceres turns out to be a livelier place than we might have imagined. Continuing analysis of data from the Dawn spacecraft is showing us an object where surface changes evidently caused by temperature variations induced by the dwarf planet's orbit are readily visible even in short time frames. Two new papers on the Dawn data are now out in Science Advances, suggesting variations in the amount of surface ice as well as newly exposed crustal material. Andrea Raponi (Institute of Astrophysics and Planetary Science, Rome) led a team that discovered changes at Juling Crater, demonstrating an increase in ice on the northern wall of the 20-kilometer wide crater between April and October of 2016. Calling this 'the first detection of change on the surface of Ceres,' Raponi went on to say: "The combination of Ceres moving closer to the sun in its orbit, along with seasonal change, triggers the release of water vapor from the subsurface, which then condenses on the cold crater wall. This causes...

The imagery we're getting of Jupiter's polar regions is extraordinary. Juno's Jovian Infrared Auroral Mapper instrument (JIRAM) works at infrared wavelengths, showing us a vivid picture of a massive central cyclone at the north pole and eight additional cyclones around it. In the image below, we're looking at colors representing radiant heat, with yellow being thinner clouds at about -13 degrees Celsius, and dark red representing the thickest clouds, at about -118 degrees Celsius. JIRAM can probe down to 70 kilometers below the cloud tops. Image: This composite image, derived from data collected by the Jovian Infrared Auroral Mapper (JIRAM) instrument aboard NASA's Juno mission to Jupiter, shows the central cyclone at the planet's north pole and the eight cyclones that encircle it. Credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM. This is hardly the orange, white and saffron belted world we are familiar with from telescope views of the lower latitudes. The scale of these storms is, as...