WORLDTECHHubble and Webb find 27 icy bodies beyond Neptune holding early solar system clues
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NASA reports that the Hubble and James Webb Space Telescopes studied 27 small objects beyond Neptune and found clues about the solar system's origins. According to the agency, these bodies appear to have kept evidence of their formation for billions of years.
Frozen leftovers of early planet building
Planets are thought to have begun as tiny particles of dust and pebbles orbiting the young Sun, which gradually joined into larger bodies. Material from that process gathered into objects roughly the size of cities, called planetesimals. Many bodies beyond Neptune never reached the final stage of growth, so a large population of smaller bodies remained instead of full planets.
These trans-Neptunian objects, or TNOs, travel around the Sun far past Neptune's orbit. According to the report, they offer a rare chance to examine the materials that eventually became planets.
Combined observations of one patch of sky
For the first time, astronomers combined observations from Hubble and Webb to study TNOs. Both telescopes watched the same region of sky at once, with Hubble capturing visible light and Webb capturing infrared light. Research teams led by PhD candidates at the University of Victoria in Canada, working with guidance from the National Research Council of Canada, and researchers at Northern Arizona University in Flagstaff carried out what NASA describes as the deepest survey of trans-Neptunian objects to date.
Most of the objects are extraordinarily faint, shining more than 100 million times more weakly than anything visible to the naked eye. Their colours matter because they indicate the chemical makeup of their surfaces.
Two groups with different histories
The researchers distinguished two groups: dynamically cold and dynamically hot TNOs. The labels describe orbital behaviour, not temperature. Cold objects have largely stayed where they formed, moving on nearly circular paths close to the plane in which most planets orbit. Hot objects first formed between the present orbits of Uranus and Neptune, but were flung outward when the giant planets shifted early in the solar system's history. Their orbits are now far more elongated and take them above and below the main orbital plane.
Despite these different histories, the two groups showed a surprising similarity: even the smallest objects appear to retain surface characteristics resembling those of their larger counterparts.
Fewer small bodies than predicted
Before the observations, scientists expected the smaller TNOs to bear clear signs of repeated collisions over billions of years. The findings instead point to fewer small objects than some theories predicted, which challenges current models of planet formation.
The studies were published in The Astronomical Journal.
Open questions
- Why are there fewer small objects beyond Neptune than some theories predicted?
- Why do the smallest bodies in both populations resemble their larger counterparts in colour?