Episode
The Smallest Things Remember
- Published
- Sep 9, 2026
- Duration seconds
- 1671
- Processing state
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- https://www.astronomydaily.io
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Summary
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 distributi…