One of the most enjoyable interviews I've been involved with lately was with Ryan Ferris, who runs the podcast Cosmic Tortoise from Christchurch, New Zealand. Ryan's questions were sharp and of a philosophic bent, plumbing issues like the purpose and direction of human exploration. From Thor Heyerdahl's extraordinary experiments at shipbuilding and navigation to the impulses that took Polynesian sailors into unknown waters as they settled Pacific islands, is there an innate human impulse to explore? We kicked all this around, along with SETI, the 'Oumuamua object, and the need for a re-orienting long-term approach to civilization. Ultima Thule and the recent exploration of it by New Horizons fit comfortably within the narrative Ryan and I discussed, as an example of satisfying that drive to push into the unknown, and also as an early marker for the growth of infrastructure in the Solar System. The Kuiper Belt pushes us hard for now, but we learn with each mission. In the meantime,...

What a lively place Neptune used to be, at least back in the days when the planet captured Triton, doubtless a Kuiper Belt Object now in a retrograde orbit around the primary. Recent work led by Mark Showalter (SETI Institute) puts the Hubble Space Telescope to work in studying one result of the sudden acquisition of so massive an object. A first generation of small satellites was likely scattered and rearranged, its debris becoming the Neptunian moons we see today. Among them is Hippocamp, once known as S/2004 N 1, which appears to be a fragment from Neptune's second largest moon Proteus. What an interesting set of observations we have here. Discovered in 2013, Hippocamp is the outermost of the planet's inner moons, and it orbits a scant 12,000 kilometers from Proteus. We can relate the 2013 discovery with what Voyager 2 found at Neptune in 1989: A large impact crater on Proteus. "The first thing we realised was that you wouldn't expect to find such a tiny moon right next to...

Sometimes the way we discover new things is by looking back, as witness the blue haze of Pluto. The image below comes, of course, from New Horizons, taken after the flyby and looking back in the direction of the Sun. Here we're looking at a mosaic combining black and white LORRI images (Long Range Reconnaissance Imager) and enhancing them with lower-resolution color data from the Ralph/Multispectral Visible Imaging Camera (MVIC). The result, taken about 3.5 hours after closest approach, is in approximately true color. Image: Pluto as seen by New Horizons from 200,000 kilometers after the flyby. The spectacular blue haze, extending to over 200 kilometers in altitude, is the result of sunlight acting on methane and other molecules in Pluto's atmosphere to produce a photochemical haze. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute. Ultima Thule likewise yields more of its secrets as we look at data from beyond the closest encounter. New...

Larry Klaes' article on the film Silent Running, with its images of Saturn originally intended for 2001: A Space Odyssey, makes today's story the obvious segue, and thus gives me the chance to catch up with some work I've been wanting to write about. For scientists using Cassini data have been able to zero in on the age of Saturn's rings, an always lively area of controversy, with evidence that the rings formed between 10 million and 100 million years ago. The new analysis is discussed in the journal Science. How to make such a call? Everything depends on getting a firmer fix on the mass of the rings, which in turn would tell us something about how bright individual ring particles must be. The brightness of the rings should have been affected by soot-like darkening inevitable over time. Fortunately, we had Cassini at Saturn to perform its so-called Grand Finale orbits, 22 dives between the planet and the rings. The gravitational effect of the rings went from being noise in data about...

"We think we are looking at the most primitive object ever imaged by a spacecraft," said Jeff Moore (NASA Ames) at today's Ultima Thule press conference. Moore, New Horizons geology and geophysics lead, went on to describe the process of innumerable particles growing into nodes amidst growing low velocity collision and interaction. We are truly looking at primordial materials with Ultima Thule, which is now revealed as a contact binary. Have a look. Image: This image taken by the Long-Range Reconnaissance Imager (LORRI) is the most detailed of Ultima Thule returned so far by the New Horizons spacecraft. It was taken at 5:01 Universal Time on January 1, 2019, just 30 minutes before closest approach from a range of 18,000 miles (28,000 kilometers), with an original scale of 730 feet (140 meters) per pixel. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute. Bear in mind that New Horizons was working with a Sun 1,900 times fainter than a sunny...

We're starting to get a better view of Ultima Thule, the next destination for the New Horizons spacecraft, which is due to make its flyby of the Kuiper Belt Object also known as 2014 MU69 on New Year's Eve (0533 UTC January 1) The images below can't help but recall the gradual approach to Pluto/Charon as New Horizons closed on what turned out to be a spectacularly successful encounter. Here's hoping Ultima Thule is just as productive in teaching us something about Kuiper Belt Objects in general. Here's hoping, too, for another KBO flyby down the road. What we see in the dual images is the view (at the left) through LORRI (Long Range Reconnaissance Imager), averaging 10 individual 30-second exposures, with Ultima Thule just barely visible in the yellow circle. The component exposures were taken about a day before a course correction maneuver on December 2 and show Ultima visible against background stars. At the right is the image re-processed to remove the background starfield....

It makes sense that planets in other stellar systems would have moons, but so far it has been difficult to find them. That's why Kepler-1625b, about 8,000 light years out in the direction of Cygnus, is so interesting. As we noted last month, David Kipping and graduate student Alex Teachey have compiled interesting evidence of a moon around this gas giant, which is itself either close to or within the habitable zone of its star. The massive candidate exomoon is the size of Neptune, and if confirmed, would mark the first exomoon detection in our catalog. As the examination of Kepler-1625b and its transit timing variations continues, we have new work out of the University of Zürich, ETH Zürich and NCCR PlanetS that adds weight to the assumption that moons around large planets should be ubiquitous. Using computer simulations run at the Swiss National Supercomputing Centre (CSCS) in Lugano, a team of researchers led by Judit Szulágyi (University of Zurich and ETH Zurich) has determined...

The outer system object called Chariklo doesn't get into the news all that much, so I'm glad that this morning I have the chance to give it its place in the Sun. 10199 Chariklo is a Centaur, moving between the orbits of Saturn and Uranus. With an estimated diameter of 250 kilometers, it's the largest Centaur known, and as far as I know, the first one known to have a ring system. Another Centaur, Chiron, is also suspected of having rings, but on the latter, researchers have not ruled out other explanations for the observed feature, like symmetrical jets of gas and dust. With Chariklo, we have data from a 2013 occultation of a distant star that revealed the existence of two rings, one 3 kilometers and the other about 7 kilometers wide, separated by about 9 kilometers. Chariklo's rings have even been given nicknames -- Olapoque for the larger, Chui for the smaller, both the names of Brazilian rivers, though the IAU will have the final say on such matters. Of particular interest since...

Extended operations at multiple targets, as Dawn showed us, are possible with ion propulsion. But we still learn much from flybys, something New Horizons reminded us with its spectacular success at Pluto/Charon, and again reminds us as it closes on MU69. Likewise, a mission called Lucy will visit multiple objects, using traditional chemical propulsion with gravity assist to achieve flybys of seven different targets. The destination: Jupiter's trojan asteroids. With launch scheduled for 2021, Lucy's will study six Jupiter trojans and one asteroid in the Main Belt. Image: Jupiter's extensive trojan asteroids, divided into 'Trojans' and 'Greeks' in a nod to Homer, but all trojans nonetheless. Credit: "InnerSolarSystem-en" by Mdf at English Wikipedia - Transferred from en.wikipedia to Commons. Licensed under Public Domain via Commons. The trojans are interesting bodies orbiting at the L4 and L5 Lagrange points 60° ahead and behind the gas giant. Jupiter's trojans are the best known...

It seems to be a week for endings. Following the retirement of the wildly successful Kepler spacecraft, we now say goodbye to Dawn following an extraordinary eleven years that took us not only to orbital operations around Vesta but then on to detailed exploration of Ceres. The spacecraft ran out of hydrazine, with the signal being lost by the Deep Space Network during a tracking pass on Wednesday. No hydrazine means no spacecraft pointing, vital in keeping Dawn's antenna properly trained on a distant Earth. I immediately checked to see if mission director and chief engineer Marc Rayman had gotten off a post on his Dawn Journal site, but he really hasn't had time to yet. It will be interesting to see what Dr. Rayman says, and it's appropriate here to thank him for the continuing updates and insights he provided throughout the Dawn mission. Keeping space exploration in front of the public is essential for continuing funding of deep space robotic missions, as both the Dawn and New...

The interstellar object called ‘Oumuamua continues to inspire analysis and speculation. And no wonder. We had limited time to observe it and were unable to obtain a resolved image to find out exactly what it looks like. This morning I want to go through a new paper from Shmuel Bialy and Abraham Loeb (Harvard University) considering the role radiation pressure from the Sun could play on this deep sky wanderer. Let’s also review what we do know about it, which I’ll do with reference to this paper’s introduction, where recent work is discussed. For it seems that each time we look at ‘Oumuamua anew, we find something else to talk about. Discovered in October of 2017 by the Pan-STARRS survey (Panoramic Survey Telescope and Rapid Response System) in Hawaii, ‘Oumuamua stood out because of its hyperbolic trajectory, flagging it as an interstellar object, the first ever discovered passing through the Solar System. The object’s lightcurve indicated both that it was tumbling and had an aspect...

To say that the Space Science and Engineering Division at Southwest Research Institute has been busy of late is quite an understatement. Alan Stern, principal investigator for New Horizons, has been leading an SwRI study examining just how we might operate an orbiter at Pluto/Charon, with results that are surprising and encouraging for the future of such a project. Working with spaceflight engineer and mission designer Mark Tapley and planetary scientist Amanda Zangari, as well as project manager John Scherrer and software lead Tiffany Finley, Stern has been looking at an orbital tour of Pluto built around a series of gravity assist maneuvers involving Charon, its large moon. The mission would use the kind of electric propulsion system we saw in the Dawn mission to Vesta and Ceres, and by clever use of gravity assists, would pull off another Dawn feat by leaving Pluto once its orbital operations were concluded and moving into the Kuiper Belt for encounters with further objects....

Europa stays in this news this morning as we continue to correlate recent observations with the invaluable results of the Galileo mission. Hubble data have played a role in this, with researchers identifying plume activity in 2013 that recalled the geysers of Enceladus, a possible indication of venting from the subsurface ocean. But analysis of Cassini data from its 2001 Jupiter flyby enroute to Saturn showed no evidence of plume activity through its ultraviolet imaging spectrograph (UVIS). So what exactly did Hubble see? Yesterday's post highlighted Julie Rathbun's contention that if they are there, Europan plumes show no thermal signature in Galileo data, while Xianzhe Jia (University of Michigan) and the SETI Institute's Melissa McGrath have used Galileo magnetometer data to support possible plume activity. We may need Europa Clipper to resolve the matter. Now the 66 dish antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) have been turned on Europa in an attempt...

One of the youngest surface features on Europa draws attention because of its possible connection with what lies beneath the Jovian moon's ice. The dark center of Pwyll crater, visible in the image below, is some 40 kilometers across, with a central peak reaching about 600 meters. At issue is the terrain resulting from the impact causing the crater. An impact perhaps 20 million years ago seems to have blown water and ice across the Europan surface. Evidence of a possible plume from Europa's ocean in this area is the subject of continuing work. The bright terrain around the crater suggests water ice, and note, too that the Pwyll impact left ejecta rays as far as the Conamara Chaos region 1000 kilometers to its north. Conamara Chaos features themselves have been studied extensively for terrain suggestive of melting and refreezing ice. We saw recently how Xianzhe Jia (University of Michigan), working with the SETI Institute's Melissa McGrath, used data from the Galileo mission to...

I love the timing of New Horizons' next encounter, just as we begin a new year in 2019. On the one hand, we'll be able to look back to a mission that has proven successful in some ways beyond the dreams of its creators. On the other hand, we'll have the first close-up brush past a Kuiper Belt Object, 2014 MU69 or, as it's now nicknamed, Ultima Thule. This farthest Solar System object ever visited by a spacecraft may, in turn, be followed by yet another still farther, if all goes well and the mission is extended. This assumes, of course, another target in range. We can't rule out a healthy future for this spacecraft after Ultima Thule. Bear in mind that New Horizons seems to be approaching its current target along its rotational axis. That could reduce the need for additional maneuvers to improve visibility for the New Horizons cameras, saving fuel for later trajectory changes if indeed another target can be found. The current mission extension ends in 2021, but another extension...

Whether or not there is an undiscovered planet lurking in the farthest reaches of the Solar System, the search for unknown dwarf planets and other objects continues. Extreme Trans-Neptunian objects (ETNOs) are of particular interest. The closest they come to the Sun is well beyond the orbit of Neptune, with the result that they have little gravitational interaction with the giant planets. Consider them as gravitational probes of what lies beyond the Kuiper Belt. Among the population of ETNOs are the most distant subclass, known as Inner Oort Cloud objects (IOCs), of which we now have three. Added to Sedna and 2012 VP113 comes 2015 TG387, discovered by Scott Sheppard (Carnegie Institution for Science), Chad Trujillo (Northern Arizona University) and David Tholen (University of Hawai?i). The object was first observed in 2015, leading to several years of follow-up observations necessary to obtain a good orbital fit. For 2015 TG387 is a challenging catch, discovered at about 80 AU from...

I always imagined Titan's surface as a relatively calm place, perhaps thinking of the Huygens probe in an exotic, frigid landing zone that I saw as preternaturally still. Then, prompted by an analysis of what may be dust storms on Titan, I revisited what Huygens found. It turns out the probe experienced maximum winds about ten minutes after beginning its descent, at an altitude of some 120 kilometers. It was below 60 kilometers that the wind dropped. And during the final 7 kilometers, the winds were down to a few meters per second. At the surface, according to the European Space Agency, Huygens found a light breeze of 0.3 meters per second. But is Titan's surface always that quiet? The Cassini probe has shown us that Titan experiences interesting weather driven by a methane cycle that operates at temperatures far below Earth's water cycle, filling its lakes and seas with methane and ethane. The evaporation of hydrocarbon molecules produces clouds that lead to rain, with conditions...

We've only orbited one object in the Solar System known to exhibit cryovolcanism, but Ceres has a lot to teach us about the subject. Unlike the lava-spewing volcanoes of Earth, an ice volcano can erupt with ammonia, water or methane in liquid or vapor form. What appear to be cryovolcanoes can be found not only on Ceres but Titan, and the phenomenon appears likely on Pluto and Charon. Neptune's moon Triton is a special case, with rugged volcanic terrain in evidence, as opposed to much smoother surfaces without obvious volcanoes elsewhere. Activity like this can be a good deal less dramatic than what we see on Earth, or spectacularly on Io. The eruption of an ice volcano involves rocks, ice and volatiles more or less oozing up out of the volcano to freeze on the surface, a process thought to be widespread on Ceres. But what happens to cryovolcanoes as they age? Ahuna Mons, an almost five-kilometer tall mountain that is no more than 200 million years old, raises the question. Why is it...

There are two senses in which we are 'looking back' at Titan in today's post. On the one hand, the New Horizons spacecraft has already taken sensors well beyond Pluto in preparation for the encounter with MU69. From its perspective, anything in the Solar System inside the Kuiper Belt is well behind. What with our Pioneers, Voyagers and now New Horizons, the human perspective has widened that far. But we're also looking back in terms of time when we revisit the Cassini mission and what it had to tell us about Saturn's moons. Below is the final view the spacecraft had of Titan's lakes and seas, a view of the north polar terrain showing the abundance of liquid methane and ethane. The view was acquired on September 11, 2017, a mere four days before Cassini was sent to its fiery end in Saturn's atmosphere as a way of avoiding any potential future contamination. Image: This view of Titan's northern polar landscape was obtained at a distance of approximately 140,000 kilometers (87,000...

Given that we’ve been talking lately about collisions and water-delivering impacts in the early days of the Solar System, it’s a natural enough segue to today’s work from the Southwest Research Institute (SwRI) on how the planets themselves may have moved about in that era. We also need to talk about the upcoming Lucy mission, which targets two interesting bodies: Patroclus and Menoetius. Both are approximately 112 kilometers wide, comprising a large binary among the Trojan asteroids, which move in leading and trailing orbits around Jupiter. Image: Jupiter’s extensive Trojan asteroids, divided into ‘Trojans’ and ‘Greeks’ in a nod to Homer, but all Trojans nonetheless. Credit: “InnerSolarSystem-en” by Mdf at English Wikipedia – Transferred from en.wikipedia to Commons. Licensed under Public Domain via Commons. What David Nesvorny and team have done in their recent paper is to look at migration of Solar System planets, with evidence they believe can be pulled from the...