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...