This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: For the first time, scientists used the combined power of NASA's Hubble and James Webb Space Telescopes to study some of the most far-flung bodies in our solar system, trans-Neptunian objects (TNOs). Some are the smallest and faintest ever directly seen.
The researchers unexpectedly found fewer small TNOs than expected and that the colors of these bodies followed the same relationships as those of their larger family members. These objects are typically small, faint, icy bodies orbiting the sun beyond the orbit of Neptune. Most are more than 100 million times dimmer than objects visible to the unaided eye.
In two complementary papers published Tuesday in The Astronomical Journal, teams analyzed the color, composition and size distribution of 27 newly discovered tiny, dim TNOs. This class of small bodies offers the best view into an early stage of planet-building, when a disk of dust and pebbles in orbit around the sun coalesced into city-sized "planetesimals"—the solid building blocks that clump together to form planets—but had not yet merged into full-size worlds. Beyond Neptune, this second stage never happened, leaving behind a frozen population of planetesimals.
In the deepest TNO survey to date, teams led by Ph.D. candidates from the University of Victoria in Canada and Northern Arizona University in Flagstaff, under the guidance of the National Research Council of Canada, examined a patch of sky simultaneously with Hubble, observing the TNOs' visible light, and Webb, observing their infrared light. The researchers measured the objects' colors, which are like fingerprints of surface composition, as well as their sizes, and determined their orbits. In the coordinated observations, 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 second type, dynamically "hot" TNOs, formed between the current locations of Uranus and Neptune but were pushed outward to their current locations 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.
Before these observations, astronomers thought that small TNOs from both the hot and cold populations would have undergone many collisions, changing their surfaces compared with larger TNOs. But that's not what the observations showed. Instead, the small bodies look like their larger counterparts.
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