NASA’s Hubble and James Webb Space Telescopes have uncovered surprising clues about the earliest days of our solar system by examining some of the smallest and faintest objects ever observed beyond Neptune. The findings challenge expectations about how planets form and suggest that these distant, icy bodies have preserved evidence of their origins for billions of years.
For the first time, astronomers combined observations from Hubble and Webb to investigate trans-Neptunian objects (TNOs), tiny bodies that travel around the Sun far beyond Neptune’s orbit. Researchers discovered 27 previously unknown objects, but their findings revealed an unexpected puzzle. There were fewer small objects than some theories predicted, and their colors closely resembled those of much larger objects in the same distant regions.
These frozen remnants offer a rare opportunity to study the materials that eventually became planets. Most are extraordinarily difficult to detect, shining more than 100 million times more faintly than objects visible to the naked eye. Two related studies published in The Astronomical Journal examined the newly identified objects to learn more about their sizes, compositions, and ancient history.
Ancient Building Blocks of the Solar System
Scientists believe planets began forming when tiny particles of dust and pebbles orbiting the young Sun gradually accumulated into larger bodies. Over time, these materials formed objects roughly the size of cities, known as “planetesimals.” These early building blocks eventually combined to create the planets we see today.
However, that final stage of growth did not occur for many objects beyond Neptune. Instead of developing into full-sized planets, countless smaller bodies remained, preserving evidence of the solar system’s earliest period of formation.
To investigate these distant survivors, research teams led by PhD candidates at the University of Victoria in Canada, working under the guidance of the National Research Council of Canada, and Northern Arizona University in Flagstaff conducted the deepest survey of trans-Neptunian objects to date. Both space telescopes observed the same region of sky simultaneously, with Hubble collecting visible light and Webb capturing infrared light.
By combining these observations, astronomers could examine the objects’ colors, estimate their sizes, and determine how they orbit the Sun. Their colors are especially valuable because they provide clues about the chemical makeup of their surfaces, much like fingerprints that reveal an object’s identity and history.
Two Populations of Distant Icy Worlds
The researchers focused on two distinct populations of trans-Neptunian objects, known as dynamically “cold” and dynamically “hot” TNOs. These descriptions refer to their orbital behavior rather than their temperatures.
Cold objects have largely remained in the regions where they originally formed. They follow relatively circular paths around the Sun and stay close to the plane in which most of the solar system’s planets orbit.
Hot objects have experienced a much more turbulent history. They originally formed between the present-day orbits of Uranus and Neptune but were scattered outward as the giant planets shifted positions early in the solar system’s development. Their current orbits are much more elongated, and they travel above and below the solar system’s main orbital plane.
Despite these dramatically different histories, the two populations revealed an unexpected similarity. Even the smallest objects appear to have retained surface characteristics resembling those of their larger counterparts.
Tiny Worlds Preserve Their Ancient Origins
Before the observations, scientists suspected that smaller TNOs would show clear evidence of repeated collisions over billions of years. Impacts could have fractured the objects and exposed fresh material, potentially changing their surface compositions and colors.
Instead, the newly discovered objects displayed the same general color relationships seen among larger TNOs. This suggests that collisions may have altered their surfaces much less than expected.
One possibility is that these objects have experienced fewer impacts than astronomers previously assumed. Another is that their surfaces somehow retain their original compositions even after collisions. Researchers have not yet determined which explanation is correct.
“You could imagine a scenario where getting knocked around and fragmented would change the surface composition, and then you would see a different surface color for tiny TNOs compared to their larger siblings. So it’s really fascinating to see that the smallest objects are somehow ‘remembering’ and preserving the history of how they were made,” said Northern Arizona University PhD candidate Anastasia Morgan, who led the study of color and composition.
“These dynamically ‘hot’ TNOs retain a signature of where they were born, even though they’ve been orbitally scrambled since then,” said co-author David Trilling of Northern Arizona University.
The observations indicate that both hot and cold TNOs have maintained color patterns linked to their formation, with surprisingly little apparent change since the solar system’s beginnings. These ancient objects may therefore preserve important information about the environments in which they first took shape.
Webb Finds Fewer Tiny Worlds Than Expected
The James Webb Space Telescope also provided another important piece of the puzzle. Its observations allowed scientists to examine how many objects exist at different sizes, revealing an unexpected resemblance between the two populations.
Although hot and cold TNOs formed in different parts of the early solar system, their overall size distributions were remarkably alike. This suggests that the processes responsible for creating planetesimals may have operated in much the same way across different environments.
“It’s very interesting that the process of planetesimal formation ends up producing the same distribution of sizes for both cold and hot populations, despite forming in different regions of the early solar system. The process seems to be insensitive to disk conditions, producing similar planetesimal sizes whether the disk is hot or cold, and dense or fluffy,” said University of Victoria PhD candidate Marielle Eduardo, who led the study on size distribution.
The researchers also identified a surprising shortage of very small TNOs compared with predictions from some existing planet formation models. Understanding why fewer objects were detected could help scientists refine their explanations of how the solar system’s original building blocks developed.
Webb’s extraordinary sensitivity made it possible to discover 27 exceptionally faint objects. One was so dim that detecting it would be comparable to standing on Earth and spotting a small swarm of fireflies on the Moon.
The smallest object measured just 3 miles (5 kilometers) across, making it approximately five times smaller than the objects detectable with even the most sensitive telescopes on the ground.
Hubble and Webb Reveal New Clues to Planet Formation
These discoveries depended on the complementary capabilities of NASA’s two powerful space observatories. Hubble’s ability to detect visible light and Webb’s sensitivity to infrared light gave scientists a more complete picture of the distant objects than either telescope could have provided independently.
Together, the telescopes have opened a new window into a largely unexplored population of ancient solar system remnants. Their surprising similarities, preserved surface characteristics, and unexpected numbers offer important clues about the processes that shaped the planets billions of years ago.
Source: www.sciencedaily.com
