Two Astronomical Journal studies found 27 newly discovered trans-Neptunian objects preserve early solar system chemical and color signatures, giving astronomers a clearer record of how planet-building bodies formed beyond Neptune.
Hubble measured visible-light colors and Webb probed infrared sizes and compositions, and together they showed the smallest TNOs look strikingly like larger ones instead of bearing the surface changes expected from billions of collisions.
Webb also detected fewer very small objects than some planet-formation models predicted, even as both dynamically cold and hot TNO populations showed similar size distributions despite forming in different regions.
One detected body is only about 5 kilometers across, underscoring Webb's sensitivity and reinforcing the idea that outer solar system planetesimal formation may have worked similarly across varied disk conditions.