Tiny Bodies Beyond Neptune Look Untouched Since the Solar System Formed
NASA said Hubble and the James Webb Space Telescope were pointed at the same patch of sky and picked out 27 previously unknown icy bodies orbiting beyond Neptune, the smallest of them about 3 miles (5 kilometers) across. Two teams report the objects' colors, sizes and orbits in two papers published Sept. 8 in The Astronomical Journal.
They are leftovers from an early stage of planet building. NASA's release describes dust and pebbles around the young Sun clumping into solid blocks the size of a city, which, beyond Neptune, never went on to become planets, and calls this class of object the best available view of that stage.
Astronomers had expected small bodies that far out to have been chipped and reshaped by collisions, which would leave them a different color from their larger relatives. The color and composition paper reports the same relationships in the small objects as in the big ones. NASA said that implies collisions are not changing the surfaces much. It also said the reason is unresolved: either there have been fewer impacts than expected, or the objects have somehow held on to their original composition.
"So it's really fascinating to see that the smallest objects are somehow 'remembering' and preserving the history of how they were made," said Anastasia Morgan, the Northern Arizona University Ph.D. candidate who led the color and composition study.
Webb's data also let the teams count how many objects there are at each size. They found fewer very small ones than some planet-formation models predict. The second paper reports that two groups with different histories (one still on nearly circular orbits, the other pushed outward when the giant planets migrated) came out with surprisingly similar size distributions. "The process seems to be insensitive to disk conditions," said Marielle Eduardo, the University of Victoria Ph.D. candidate who led that work.
The smallest object in the survey is about five times smaller than the most sensitive ground-based telescopes can detect, according to NASA. Hubble collected the visible light and Webb the infrared, and the agency says neither telescope could have produced the result alone and that this is the first time the pair has been used together on objects beyond Neptune.
