NASA's Webb and Hubble reveal how tiny objects beyond Neptune still preserve their ancient origins

For billions of years, the smallest objects in the solar system have been passing unnoticed in the darkness, too faint for astronomers to study properly—until two of NASA's most powerful space telescopes, Hubble and James Webb, looked at them together. Now, scientists are getting a closer look at what these distant objects have managed to preserve.

What are these distant objects?

These distant objects are called Trans-Neptunian Objects (TNOs). The name might sound scary at first, but they are actually some of the most interesting objects to study in our solar system. Trans-Neptunian simply means objects that are found beyond Neptune. If we look at the solar system in order, it starts with the Sun, followed by the planets, with Neptune as the farthest major planet. Beyond Neptune, far away from the Sun, we find these distant, icy objects.

TNOs are small bodies mainly made of ice and rock. They are generally considered leftover pieces from the formation of the solar system. This makes them very interesting to scientists because studying them can help us understand how the solar system formed and what the conditions were like when it was very young.

How did scientists find them?

The biggest hurdle for the researchers is that these icy objects are very far away from Earth, ranging from approximately 30 to over 100 astronomical units (AU). One AU is about 93 million miles (150 million kilometers), so these objects can be billions of miles away. They are also very dim and extremely small. Being beyond Neptune makes them difficult to observe directly from Earth.

Therefore, to study these objects, scientists used the Hubble Space Telescope and James Webb Space Telescope (JWST) in tandem. One thing to note here—scientists have not just used Webb to discover these icy objects, but they used Hubble and Webb simultaneously to identify these objects and study them.

Rather than looking at different times, the researchers pointed both telescopes at the exact area of the sky, using Hubble to observe the TNOs in visible light, and Webb to observe them in infrared. Using their combined power, scientists tracked how these faint specks of light moved across the sky over time against the fixed background stars, and were able to determine their orbits. Using both visible and infrared observations, scientists also learned more about the TNOs' colors, brightness, and surface properties.

What did Hubble and Webb discover?

Scientists combined the observations from both telescopes and identified 27 new Trans-Neptunian Objects. The most intriguing part is that some of these objects are extremely small—the smallest objects are around 5 km, which is about 3 miles wide. Despite being so far away, scientists were able to detect these faint objects by relying on the unprecedented sensitivity of the two space telescopes.

But that's not all. Scientists studied the brightness and colors of these icy objects. From this, they can learn about their surfaces because different materials reflect and absorb light in different ways. Before the actual study, scientists expected that they would find differences between large and small TNOs. The reason for this thinking was that these objects have been traveling across our solar system for billions of years. Because of constant collisions over eons, scientists assumed the small objects would have been heavily fragmented. If an ice rock is hit repeatedly, its primordial outer layers should be stripped away, exposing fresh ice and changing its overall color.

But the observations gave surprising results: Small TNOs showed similar surface properties and colors to large TNOs, meaning no significant change was observed as scientists had expected. This possibly suggests that these objects have preserved some information about the early solar system. As Anastasia Morgan, a PhD candidate at Northern Arizona University who led the study of the TNOs' color and composition, explained, "it's really fascinating to see that the smallest objects are somehow 'remembering' and preserving the history of how they were made."

What does this tell us about the early Solar System?

Another thing scientists looked at in these observations was the different sizes of TNOs and how many of them exist. According to their models, they expected to find more small TNOs, but the observations showed fewer than expected.

This difference is important because it gives scientists a new clue about how these distant objects formed and changed over time. It also suggests that there may still be something missing from our understanding of how the small building blocks of the Solar System evolved. This data can help scientists improve their models and get a better idea of what happened in the early solar system.

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