Free Astronomy Magazine November-December 2026

52 NOVEMBER-DECEMBER 2026 ASTRO PUBLISHING The team of researchers measured the objects’ col- ors, which are like a finger- print of the surface com- position, as well as their sizes and determined their orbits. In the coordinated observa- tions, the teams studied two different types of TNOs. The first, dynamically “cold” TNOs, are on their original, relatively circular orbits around the Sun in the plane of the solar system. The sec- ond type, dynamically “hot” TNOs, formed between the current locations of Uranus and Neptune but were pushed outward where they are today when the outer gas giants migrated early in the solar system’s history. Today they reside in highly elliptical orbits and move in and out of the plane of our solar system. Prior to these observations, astron- omers thought that small TNOs from both hot and cold populations would have undergone many colli- sions, changing their surfaces com- pared to larger TNOs. But that’s not what the observations showed. In- stead, the small bodies look like their larger counterparts. This im- plies that collisions are not changing the surfaces significantly—perhaps because there are fewer collisions than expected, or because the TNOs somehow retain their primordial, pre-collision compositions. The teams are still trying to unravel this mys- tery. “You could imagine a scenario where getting knocked around and fragmented would change the sur- face composition, and then you would see a different surface color for tiny TNOs compared to their larger siblings. So it’s really fascinat- ing to see that the smallest objects are somehow ‘remembering’ and https://www.youtube.com/watch?v=KDQYSUR0F1o T his video explains how Hubble and Webb are giving scientists a new look at some of the solar system’s oldest survivors and revealing new clues about how the building blocks of planets, including Earth, first formed. [NASA’s Goddard Space Flight Center. Paul Morris: Lead Producer] The process seems to be insensitive to disk conditions, producing similar planetesimal sizes whether the disk is hot or cold, and dense or fluffy,” said University of Victoria PhD can- didate Marielle Eduardo, who led the study on size distribution. Researchers also found fewer of these very small bodies than they ex- pected based on some planet forma- tion models. Webb discovered 27 new, remarkably dim TNOs, one so faint it is equivalent to standing on Earth and seeing a small swarm of fireflies on the Moon. The smallest one they observed has a diameter of about 3 miles (5 kilometers), which is about five times smaller than what is possible to detect with the most sensitive ground-based telescopes. This project would not have been possible without Hubble and Webb working together to detect and characterize these TNOs. With Hub- ble’s sensitivity in visible light and Webb’s in infrared, the space tele- scopes provide more insights than either can on its own. preserving the history of how they were made,” said Northern Arizona University PhD candidate Anastasia Morgan, who led the study of color and composition. “These dynamically ‘hot’ TNOs re- tain a signature of where they were born, even though they’ve been or- bitally scrambled since then,” added co-author David Trilling of Northern Arizona University. Both the “hot” and “cold” popula- tions seem to keep the same colors as when they were formed, with lit- tle change since the birth of the solar system. The Webb data also allowed re- searchers to measure the number of objects of each size. They found that the overall size distributions for both populations were surprisingly similar. “It’s very interesting that the process of planetesimal formation ends up producing the same distribution of sizes for both cold and hot popula- tions, despite forming in different regions of the early solar system. !