Best glimpse ever into icy planetesimals of the early solar system

The findings were published today in natural astronomy, Revealed the distribution of ice in the early solar system and how they evolved as starfish objects moved inward into the giant planet region between Jupiter and Saturn and became the constellation Centauri.

TNOs are small celestial bodies, or “planetesimals,” that orbit the Sun beyond Pluto. They were never accreted onto planets, but instead served as pristine time capsules, preserving important evidence of the molecular processes and planetary migrations that shaped the solar system billions of years ago. These solar system objects are like icy asteroids with orbits comparable to or larger than Neptune’s.

Before the new UCF-led study, TNOs were thought to be a diverse group based on orbital properties and surface color, but the molecular makeup of these objects remained poorly understood. For decades, this lack of detailed knowledge hindered the interpretation of their color and dynamic diversity. Now, new results solve the long-standing problem of explaining color diversity by providing information on composition.

“With this new study, we can understand diversity more fully, and the pieces of the puzzle are starting to fit together,” said Noemi Pinilla-Alonso, the study’s lead author.

“For the first time, we have identified the specific molecules responsible for the remarkable diversity of spectra, colors and albedos observed in trans-Neptunian objects,” said Pinilla-Alonso. “These molecules – such as water ice, carbon dioxide, methanol and complex organic matter—allowing us to directly link the spectral signature of TNO to its chemical composition.”

Using the James Webb Space Telescope (JWST), researchers found that TNO can be divided into three distinct compositional groups, with its shape formed by ice-retaining lines that existed when the solar system was formed billions of years ago.

These lines were identified as regions where temperatures were cold enough for specific ices to form and survive within the protoplanetary disk. These regions, defined by distance from the Sun, mark key points in the temperature gradient of the early solar system and provide a direct link between the conditions in which asteroids formed and their present-day composition.

Rosario Brunetto, second author of the paper and a researcher at the National Center for Scientific Research at the Institute of Space Astrophysics of the University of Paris-Saclay, said that these results are related to the formation of planetesimals in the protoplanetary disk and their subsequent evolution. The first clear connection. This work reveals how the spectral and dynamical distributions observed today emerged in planetary systems shaped by complex dynamical evolution, he said.

“The composition of TNOs is not evenly distributed among objects with similar orbits,” Brunetto said. “For example, the cold classical matter formed in the outermost region of the protoplanetary disk belongs entirely to a category dominated by methanol and complex organic matter. In comparison, the origin of TNOs in orbits associated with the Oort cloud is closer to giant giants. Planets, are all part of a spectral group characterized by water ice and silicates.

Three groups defined by surface composition behave reveal qualities that suggest the compositional structure of the protoplanetary disk.

“This supports our understanding of the materials available that helped form extrasolar objects, such as the gas giants and their moons or Pluto and other inhabitants of the trans-Neptune region,” she said.

In a complementary study of centaurs published in the same volume natural astronomyThe researchers discovered unique spectral signatures distinct from TNO, revealing the presence of a dusty regolith mantle on its surface.

This discovery about Centauri helps explain how Neptune shifted its orbit to Neptune in the giant planet region after a close gravitational encounter with Neptune. This helps shed light on how Neptune warms and sometimes develops as it gets closer to the sun. How the Comet-Like Process Became Centaur.

Their work shows that all observed Centauri surfaces exhibit special features compared to the surfaces of Haitian stars, suggesting they have changed during their passage into the inner solar system.

Pinilla-Alonso said that of the three TNO surface types, two were observed in the centaur population—bowls and cliffs, both of which lack volatile ice.

In Centaur, however, these surfaces show a distinctive feature: They are covered in a layer of dusty regolith mixed with ice, she said.

“Interestingly, we discovered a new surface class that does not exist in the Sea-Sky fabric, similar to ice-poor surfaces, cometary nuclei and active asteroids in the inner solar system,” she said.

Javier Licandro, a senior researcher at the Canary Institute of Astronomy (IAC, Tenerife, Spain) and lead author of the Centauri study, said the spectral diversity observed in Centauri was greater than expected. of more broadly, suggesting that existing models of their thermal and chemical evolution may require refinement.

For example, Likandro said, the diversity of organic features and the magnitude of the observed radiation effects were not fully anticipated.

“The diversity of water, dust and complex organic matter detected in the centaur population suggests that TNO populations have different origins and different stages of evolution, highlighting that centaurs are not a homogeneous group, but rather Dynamic and Transitional Objects. “The thermal evolution effects observed in the surface composition of Centauri are critical for establishing relationships between starfish and other populations of small bodies, such as the irregular moons of the giant planets and their Trojan asteroids. “

Study co-author Charles Schambeau, a planetary scientist at UCF’s Florida Space Institute (FSI) who specializes in centaurs and comets, emphasized the importance of these observations and that some centaurs can be observed with DiSCo TNO falls into the same category.

“This is very profound because when TNO transitions into Centauri, it goes through a warmer environment and both the ice and material on the surface change,” Schambeau said. “But clearly, in some cases, the surface changes Small enough that a single centaur can be linked to its parent TNO population. TNOs are of different spectral types than centaurs, but similar enough to be linked.”

How the research is done

These studies are part of the Discovering the Surface Composition of Neptune’s Objects (DiSCo) project led by Pinilla-Alonso, which aims to reveal the molecular composition of Neptune’s objects. Pinilla-Alonso is now Distinguished Professor at the Institute of Space Science and Technology of Asturias at the University of Oviedo and works as a planetary scientist at FSI.

In these studies, the researchers used JWST, launched about three years ago, which provides an unprecedented view of TNO and Centaur surface molecular diversity through near-infrared observations, overcoming the limitations of ground-based observations and other available instruments. .

In the TNO study, researchers used JWST to measure the spectra of 54 TNOs, capturing the detailed light patterns of these objects. By analyzing these highly sensitive spectra, researchers can identify specific molecules on its surface. Using clustering techniques, TNOs were classified into three distinct groups based on their surface composition. The groups are nicknamed “bowls,” “double dips,” and “cliffs” because of the shape of their light-absorbing patterns.

They found:

• Bowl type TNO Constituting 25% of the sample, it is characterized by strong water ice absorption and dusty surfaces. They show clear signs of crystallized water ice and have low reflectivity, indicating the presence of dark refractory material.

• Double bottom TNO Constituting 43% of the sample, it shows a strong carbon dioxide (CO2) band and some signs of complex organic matter.

• Cliff TNO Accounting for 32% of the sample, it has strong signs of complex organic matter, methanol and nitrogen-containing molecules, and is the reddest in color.

In the Centaur study, researchers observed and analyzed the reflectance spectra of five centaurs (52872 Okyrhoe, 3253226 Thereus, 136204, 250112 and 310071). This allowed them to identify the centaur’s surface composition, revealing considerable diversity among the observed samples.

They found that Thereus and 2003 WL7 belong to the bowl type, while 2002 KY14 belongs to the cliff type. The remaining two Centaurs, Okyrhoe and 2010 KR59, do not fit into any existing spectral categories and are classified as “shallow” due to their unique spectra. This newly defined group is characterized by a high concentration of primordial comet-like dust and little to no volatile ices.

Previous research and next steps

Pinilla-Alonso said that previous DiSCo research revealed the widespread presence of carbon oxides on the surface of TNO, which was a major discovery.

“Now, we build on this discovery to provide a more comprehensive understanding of the surface of the Haitian tissue,” she said. “One of the biggest realizations is that water ice, previously thought to be the most abundant surface ice, is not as common as we once thought. Instead, carbon dioxide (CO2)₂)—a gas at Earth temperatures—and other carbon oxides, such as supervolatile carbon monoxide (CO), were found in large numbers of bodies.

Harvison said the new study’s results are just the beginning.

“Now that we have general information about the identified groups of ingredients, we still have much more to explore and discover,” she said. “As a community, we can begin to explore the specific details that gave rise to these groups we see today.”

The research was funded by NASA’s Space Telescope Science Institute.