New Delhi: Some of the oldest surviving remnants of our solar system may be preserving clues about how planets formed billions of years ago.
Using NASA’s Hubble and James Webb Space Telescopes together, astronomers have discovered 27 previously unknown objects beyond Neptune. They found that these tiny, icy bodies retain characteristics that could reveal the conditions in which they were created.
The findings, published in two companion papers in The Astronomical Journal on 8 September, offer a closer look at trans-Neptunian objects (TNOs). These are small, faint bodies that orbit the Sun beyond Neptune, including objects in the Kuiper Belt. Most are more than 100 million times dimmer than anything visible to the naked eye.
Frozen remnants of planet formation
TNOs are particularly valuable to astronomers because they preserve material from an early stage of planet formation. Billions of years ago, a disk of dust and small particles surrounding the young Sun gradually came together to form larger solid bodies called planetesimals. These eventually became the building blocks of planets.
Beyond Neptune, however, many of these objects never developed into larger worlds. They remained frozen remnants of the early solar system.
The research teams used Hubble to observe visible light and Webb to capture infrared light from the same region of space beyond the blue ice giant. Combining the observations allowed them to measure the objects’ colours, sizes and orbits.
The researchers identified two broad populations. Dynamically “cold” TNOs remain in relatively circular orbits close to the plane of the solar system. “Hot” TNOs, meanwhile, are believed to have formed closer to the giant planets before being pushed into more distant, elongated orbits as Uranus and Neptune migrated.
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Objects that remember their origins
One of the most surprising findings concerned the objects’ surface colours. Astronomers had expected smaller TNOs to have undergone more collisions, which would have altered their surfaces and made them look different from larger objects.
Instead, the smaller bodies retained similar colour patterns to their larger counterparts, suggesting that their original surface compositions have remained relatively undisturbed.
“You could imagine a scenario where getting knocked around and fragmented would change the surface composition, and then you would see a different surface colour for tiny TNOs compared to their larger siblings,” said Anastasia Morgan of Northern Arizona University to NASA, who led the study examining their colours and composition.
“So it’s really fascinating to see that the smallest objects are somehow ‘remembering’ and preserving the history of how they were made,” Morgan added.
The second study further examined the distribution of objects by size. Researchers found that the hot and cold populations had surprisingly similar size distributions, despite forming in different regions of the early solar system. They also discovered fewer very small objects than some planetary formation models had predicted.
Webb detected objects as small as approximately five kilometres across, including one so faint that its detection would be comparable to spotting a small swarm of fireflies on the Moon from Earth.
Together, the findings offer a new way to investigate the early conditions that shaped our planetary neighbourhood. They also demonstrate how combining observations across different wavelengths can reveal details about objects that would otherwise remain almost impossible to study.
(Edited by Insha Jalil Waziri)