The Smallest Things Remember

Everything beyond Neptune is a leftover. The icy bodies of the Kuiper Belt never got assembled into a planet, and out there — dark, cold and empty enough that things mostly leave each other alone — they are the closest thing we have to the original building blocks of the solar system, still sitting roughly where they were made. The trouble is that everything we know about them, we learned from the big ones. Ground-based telescopes stop at around twenty-five kilometres. In two papers published on 8 September in The Astronomical Journal, teams using Hubble and Webb simultaneously — one telescope in visible light, one in the infrared, on the same field at the same moment — report twenty-seven previously unknown trans-Neptunian objects, the faintest ever directly detected. The smallest is about five kilometres across. NASA's own description of the faintest of them: the equivalent of standing on Earth and picking out a small swarm of fireflies on the Moon. The surprise is the colours. Objects that small are assumed to be collision fragments, and a fragment should be showing us the fresh ice under the irradiated red rind — so the small population should look bluer and messier than the large one. It doesn't. Led by Anastasia Morgan at Northern Arizona University, the colour study finds the small objects carry the same colour relationship as their large counterparts, in both the dynamically cold population that formed in place and the dynamically hot population that was flung outward during the giant planets' migration. David Trilling: these hot objects 'retain a signature of where they were born, even though they've been orbitally scrambled since then.' The companion size-distribution study, led by Marielle Eduardo at the University of Victoria, finds the same size distribution in both populations despite their different birthplaces. Together the two results point away from small TNOs being rubble and towards planetesimals that formed quickly, at large sizes — the picture Arrokoth gave us up close in 2019. Then: Anak Krakatau. The Sunda Strait volcano went into a major explosive phase on 5 September that ran more than twenty-four hours, throwing ash to 15,000 metres — 50,000 feet — to the west. Eight airports closed across Java and Sumatra, 2,961 flights grounded, around 170,000 travellers stranded. NASA's Earth Observatory published Landsat 8 and Suomi NPP imagery on 9 September. The whole warning chain runs through orbit: geostationary Himawari-9 imaging the full disc every ten minutes, feeding the Darwin Volcanic Ash Advisory Centre run by Australia's Bureau of Meteorology — because ash doesn't show up on aircraft weather radar, and the only warning a crew gets comes up from the ground. ESA closed out the 26-year Cluster mission by flying its last two satellites, Samba and Tango, into the atmosphere over the South Pacific near Tonga on 31 August and 1 September — deliberately, and precisely enough that a chartered business jet carrying thirty instruments could be underneath them. The ROSIE campaign, led by Jiří Šilha of Astros Solutions, got about fifty seconds on each spacecraft, measuring not the light show but the chemistry: titanium, sodium, potassium and aluminium, and specifically aluminium oxide, whose effect on ozone at those altitudes is a genuinely open question as constellations scale. ESA's Draco mission in 2027 will record the same process from the inside. And a study from the Instituto de Astrofísica de Canarias, published in Astronomy & Astrophysics and released on 4 September, finds that Messier 74 — the Phantom Galaxy — is more than twice the size the catalogues give it. Deep imaging with a one-metre telescope, about ten times deeper than Sloan, traces a disc of young stars out to roughly 100,000 light years against a catalogued 45,000. Mean age in that outer region: 640 million years. The likely cause is a close pass by the neighbouring galaxy UGC 1176 about a billion years ago. Skywatch covers both hemispheres on a New Moon week — the galactic core overhead from Sydney in its last strong month, the Teapot low in the south for North America, Venus building to greatest brilliancy on the 18th, Saturn climbing towards its 4 October opposition, and the full ISO 12312-2 safety passage for anyone tempted to hunt Venus in daylight. Links & sources NASA — NASA's Hubble, Webb Find Far-out Solar System Objects 'Remember' Past — https://science.nasa.gov/missions/hubble/nasas-hubble-webb-find-far-out-solar-system-objects-remember-past/ Morgan et al. — colours of small trans-Neptunian objects, The Astronomical Journal (8 Sept 2026) — https://doi.org/10.3847/1538-3881/ae907f Eduardo et al. — size distribution of small trans-Neptunian objects, The Astronomical Journal (8 Sept 2026) — https://doi.org/10.3847/1538-3881/ae9084 NASA Earth Observatory — Anak Krakatau Rumbles Again (Image of the Day, 9 Sept 2026) — https://science.nasa.gov/earth/earth-observatory/anak-krakatau-rumbles-again/ ANTARA News —...