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...