Chiron belongs to the class of objects that astronomers call 鈥淐entaurs.鈥� Centaurs are space objects that orbit the sun between Jupiter and Neptune. They are akin to the mythological creature they borrow their name from in that they are hybrid, possessing characteristics of both asteroids and comets.

Using the James Webb Space Telescope, 麻豆原创 (FSI) scientists recently led a team that found, for the first time, that Chiron has surface chemistry unlike other centaurs. Its surface has both carbon dioxide and carbon monoxide ice along with carbon dioxide and methane gases in its coma, the cloud-like envelope of dust and gas surrounding it.

The researchers鈥� results were recently published in the journal .

麻豆原创 FSI Associate Scientist Noem铆 Pinilla-Alonso, who now works at the University of Oviedo in Spain, and Assistant Scientist Charles Schambeau led the research. The new findings build upon prior discoveries from Pinilla-Alonso and colleagues that detected carbon monoxide and carbon dioxide ice on trans-Neptunian objects (TNOs) for the first time earlier this year.

Those observations, paired with ones of Chiron, are creating foundational knowledge for understanding the creation of our Solar System, as these objects have largely remained unchanged since the Solar System was formed, Pinilla-Alonso says.

鈥淎ll the small bodies in the Solar System talk to us about how it was back in time, which is a period of time we can鈥檛 really observe anymore,鈥� she says. 鈥淏ut active centaurs tell us much more. They are undergoing transformation driven by solar heating and they provide a unique opportunity to learn about the surface and subsurface layers.鈥�

Since Chiron possesses characteristics of both an asteroid and a comet, it makes it rich for studying many processes that could assist in understanding them, she says.

鈥淲hat is unique about Chiron is that we can observe both the surface, where most of the ices can be found, and the coma, where we see gases that are originating from the surface or just below it,鈥� Pinilla-Alonso says. 鈥淭NOs don鈥檛 have this kind of activity because they鈥檙e too far and too cold. Asteroids don鈥檛 have this kind of activity because they don鈥檛 have ice on them. Comets, on the other hand, show activity like centaurs, but they are typically observed closer to the sun, and their comas are so thick that they complicate the interpretations of observations of the ices on the surface. Discovering which gases are part of the coma and their different relationships with the ices on the surface help us learn the physical and chemical properties, such as the thickness and the porosity of the ice layer, its composition, and how irradiation is affecting it.鈥�

The discovery of these ices and gases on an object as distant as Chiron 鈥� observed near its farthest point from the sun 鈥� is exciting because it could help contextualize other centaurs and provide insight into the earliest era of our Solar System, Schambeau says.

鈥淭hese results are like nothing we鈥檝e seen before,鈥� he says. 鈥淒etecting gas comae around objects as far away from the sun as Chiron is very challenging, but JWST has made it accessible. These detections enhance our understanding of Chiron鈥檚 interior composition and how that material produces the unique behaviors as we observe Chiron.鈥�

Schambeau specializes in studying centaurs, comets and other space objects. He analyzed the methane gas coma and determined that the outflowing gas detected was consistent with it being sourced from a surface area that was exposed to the most heating from the sun.

Chiron, first discovered in 1977, is characterized much better than most centaurs and comparatively is unique, Schambeau says. The newly analyzed information helps scientists better understand the thermophysical process going on in Chiron that produces methane gas, he says.

鈥淚t鈥檚 an oddball when compared to the majority of other Centaurs,鈥� Schambeau says. 鈥淚t has periods where it behaves like a comet, it has rings of material around it, and potentially a debris field of small dust or rocky material orbiting around it. So, many questions arise about Chiron鈥檚 properties that allow these unique behaviors.鈥�

The researchers concluded that the coexistence of the molecules in various states adds another layer of intrigue for studying comets and centaurs. The study also highlighted the presence of irradiated byproducts of methane, carbon monoxide and carbon dioxide that will require further research and could help scientists further reveal the unique processes producing Chiron鈥檚 surface composition.

Chiron originated from the TNO region and has traveled around our Solar System since its creation, says Pinilla-Alonso. The orbits of Chiron and many other large non-planetary objects occasionally experience close encounters with one of the giant planets where the gravitational pull from the planet changes the smaller object鈥檚 orbit, taking them all over our Solar System and exposing them to many different environments, she says.

鈥淲e know it has been ejected from the TNO population and is only now transiting through the region of the giant planets, where it will not stay for too long,鈥� Pinilla-Alonso says. 鈥淎fter about 1 million years, centaurs like Chiron typically are ejected from the giant planets region, where they may end their lives as Jupiter Family comets or they may return to the TNOs region.鈥�

Pinilla-Alonso notes that the JWST鈥檚 spectra showed for the first time Chiron鈥檚 plethora of ices with different volatilities and their formation processes, she says.

Some of these ices, such as methane, carbon dioxide, and water ice, may be primordial components of Chiron inherited from the pre-solar nebula. Others, such as acetylene, propane, ethane, and carbon oxide, could have formed on the surface because of reduction and oxidation processes, she says.

鈥淏ased on our new JWST data, I鈥檓 not so sure we have a standard centaur,鈥� Pinilla-Alonso says. 鈥淓very active centaur that we are observing with JWST shows some peculiarity. But they cannot be all outliers. There must be something that explains why they appear to all behave differently or something that is common between them all that we cannot yet see.鈥�

The analysis of Chiron鈥檚 gases and ices opens new frontiers and opportunities for exciting research, she says.

鈥淲e鈥檙e going to follow up with Chiron,鈥� Pinilla-Alonso says. 鈥淚t will come closer to us, and if we can study it at nearer distances and get better reads on the quantities and nature of the ices, silicates, and organics, we will be able to better understand how seasonal insolation variations and different illumination patterns can affect its behavior and its ice reservoir.鈥�

The JWST is the world鈥檚 premier space science observatory, and it is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe. The JWST is an international collaboration led by NASA with its partners the European Space Agency and the Canadian Space Agency.

Researchers鈥� Credentials

Pinilla-Alonso was a professor at FSI who joined 麻豆原创 in 2015. Most of her work on this project was conducted while she was at 麻豆原创. Pinilla-Alonso also holds a joint appointment as a research professor in 麻豆原创鈥檚聽聽and has led numerous international observational campaigns in support of NASA missions, such as New Horizons, OSIRIS-REx and Lucy. Pinilla-Alonso is a distinguished professor at the Institute for Space Sciences and Technologies in Asturias, within the Universidad de Oviedo. She received her doctoral degree in astrophysics and planetary sciences from the Universidad de La Laguna in Spain.

Schambeau is an assistant scientist who received his doctoral degree in physics with a concentration in planetary sciences in 2018 from 麻豆原创. He subsequently joined FSI where he expanded upon his work examining comets and centaurs as part of 麻豆原创鈥檚聽.

A research team, led by planetary scientists M谩rio Nascimento De Pr谩 and Noem铆 Pinilla-Alonso from the 麻豆原创’s Florida Space Institute (FSI), made the findings by using the infrared spectral capabilities of the James Webb Space Telescope (JWST) to analyze the chemical composition of 59 trans-Neptunian objects and Centaurs.

The pioneering study, published this week in Nature Astronomy,聽suggests that carbon dioxide ice was abundant in the cold outer regions of the protoplanetary disk, the vast rotating disk of gas and dust from which the solar system formed. Further investigation is needed to understand the carbon monoxide ice鈥檚 origins, as it also prevalent on the TNOs in the study.

The researchers reported the detection of carbon dioxide in 56 TNOs and carbon monoxide in 28 (plus six with dubious or marginal detections), out of a sample of 59 objects observed with the JWST. Carbon dioxide was widespread on the surfaces of the trans-Neptunian population, independent of the dynamical class and body size while carbon monoxide was detected only in objects with a high carbon dioxide abundance, according to the study.

The work is part of the 麻豆原创-led Discovering the Surface Compositions of Trans-Neptunian Objects program (DiSCo-TNOs), one of the JWST programs focused on analyzing our solar system.

鈥淚t is the first time we observed this region of the spectrum for a large collection of TNOs, so in a sense, everything we saw was exciting and unique,鈥� says de Pr谩, who co-authored the study. 鈥淲e did not expect to find that carbon dioxide was so ubiquitous in the TNO region, and even less that carbon monoxide was present in so many TNOs.鈥�

The discovery of the ices can further help us understand the formation of our solar system and how celestial objects may have migrated, he says.

鈥淭rans-Neptunian Objects are relics from the process of planetary formation,鈥� de Pr谩 says. 鈥淭hese findings can impose important constraints about where these objects were formed, how they reached the region they inhabit nowadays, and how their surfaces evolved since their formation.聽Because they formed at greater distances to the Sun and are smaller than the planets, they contain the pristine information about the original composition of the protoplanetary disk.鈥�

Chronicling Ancient Ice

Carbon monoxide ice was observed on Pluto by the New Horizons probe, but not until JWST was there an observatory powerful enough to pinpoint and detect traces of carbon monoxide ice or carbon dioxide ice on the largest population of TNOs.

Carbon dioxide is commonly found in many objects in our solar system. So, the DiSCo team was curious to see if it existed in greater quantities beyond the reaches of Neptune.

Possible reasons for the lack of previous detections of carbon dioxide ice on TNOs include a lower abundance, non-volatile carbon dioxide becoming buried under layers of other less volatile ices and refractory material over time, conversion into other molecules through irradiation, and simple observational limitations, according to the study.

The discovery of carbon dioxide and carbon monoxide on the TNOs provides some context while also raising many questions, de Pr谩 says.

鈥淲hile the carbon dioxide was probably accreted from the protoplanetary disk, the origin of the carbon monoxide is more uncertain,鈥� he says. 鈥淭he latter is a volatile ice even in the cold surfaces of the TNOs. We can鈥檛 rule out the carbon monoxide was primordially accreted and somehow was retained until present date.聽However, the data suggests that it could be produced by the irradiation from carbon-bearing ices.鈥�

An Avalanche of Answers

Confirming the presence of carbon dioxide and carbon monoxide on TNOs opens many opportunities to further study and quantify how or why it is present, says Pinilla-Alonso, who also co-authored the study and leads the DiSCo-TNOs program.

鈥淭he discovery of carbon dioxide on trans-Neptunian objects was thrilling, but even more fascinating were its characteristics,鈥� she says. 鈥淭he spectral imprint of carbon dioxide revealed two distinct surface compositions within our sample. In some TNOs, carbon dioxide is mixed with other materials like methanol, water ice, and silicates. However, in another group 鈥� where carbon dioxide and carbon monoxide are major surface components 鈥� the spectral signature was strikingly unique. This stark carbon dioxide imprint is unlike anything observed on other solar system bodies or even replicated in laboratory settings.鈥�

It now seems clear that when carbon dioxide is abundant, it appears isolated from other materials, but this alone doesn’t explain the band shape, Pinilla-Alonso says. Understanding these carbon dioxide bands is another mystery, likely tied to their unique optical properties and how they reflect or absorb specific colors of light, she says.

It was commonly theorized that perhaps carbon dioxide may be present in TNOs as carbon dioxide exists in a gaseous state in comets, which are comparable in composition, Pinilla-Alonso says.

鈥淚n comets, we observe carbon dioxide as a gas, released from the sublimation of ices on or just below the surface,鈥� she says. 鈥淗owever, since carbon dioxide had never been observed on the surface of TNOs, the common belief was that it was trapped beneath the surface. Our latest findings upend this notion. We now know that carbon dioxide is not only present on the surface of TNOs but is also more common than water ice, which we previously thought was the most abundant surface material. This revelation dramatically changes our understanding of the composition of TNOs and suggests that the processes affecting their surfaces are more complex than we realized.鈥�

Thawing the Data

Study co-authors Elsa H茅nault, a doctoral student at the Universit茅 Paris-Saclay鈥檚 Institut d’Astrophysique Spatiale, and French National Center of Scientific Research, and Rosario Brunetto, H茅nault鈥檚 supervisor, brought a laboratory and chemical perspective into the interpretation of JWST observations.

H茅nault analyzed and compared the absorption bands of carbon dioxide and carbon monoxide across all objects. While there was ample evidence of the ice, there was a great diversity in abundance and distribution, H茅nault says.

鈥淲hile we found CO2 to be ubiquitous across TNOs, it is definitely not uniformly distributed,鈥� she says. 鈥淪ome objects are poor in carbon dioxide while others are very rich in carbon dioxide and show carbon monoxide. Some objects display pure carbon dioxide while others have it mixed with other compounds. Linking the characteristics of carbon dioxide to orbital and physical parameters allowed us to conclude that carbon dioxide variations are likely representative of the objects鈥� different formation regions and early evolution.鈥�

Through analysis, it is very likely that carbon dioxide was present in the protoplanetary disk, however, carbon monoxide is unlikely to be primordial, H茅nault says.

鈥淐arbon monoxide could be efficiently formed by the constant ion bombardment coming from our sun or other sources,鈥� she says. 鈥淲e are currently exploring this hypothesis by comparing the observations with ion irradiation experiments that can reproduce the freezing and ionizing conditions of TNO surfaces.鈥�

The research brought some definite answers to longstanding questions dating back to the discovery of TNOs nearly 30 years ago, but researchers still have a long way to go, H茅nault says.

鈥淥ther questions are now raised,鈥� she says. 鈥淣otably, considering the origin and evolution of the carbon monoxide. The observations across the complete spectral range are so rich that they will definitely keep scientists busy for years to come.鈥�

Although the DiSCo program observations are nearing a conclusion, the analysis and discussion of the results still have a long way to go. The foundational knowledge gained from the study will prove to be an important supplement for future planetary science and astronomy research, de Pr谩 says.

鈥淲e have only scratched the surface of what these objects are made of and how they came to be,鈥� he says. 鈥淲e now need to understand the relationship between these ices with the other compounds present in their surfaces and understand the interplay between their formation scenario, dynamical evolution, volatile retention and irradiation mechanisms throughout the history of the solar system.鈥�

Team Effort

Study co-authors also included Ana Carolina de Souza Feliciano, Charles Schambeau, Yvonne Pendelton, Dale Cruikshank and Brittany Harvison with 麻豆原创; Bryan Holler and John Stansberry with the Space Telescope Science Institute; Jorge Carvano with the Observatorio Nacional do Rio de Janeiro in Brazil; 聽Javier Licandro and Vania Lorenzi with the Instituto de Astrof铆sica de Canarias in Spain; Thomas M眉ller with the Max-Planck-Institut f眉r extraterrestrische Physik in Germany; Nuno Peixinho with the Instituto de Astrof铆sica e Ciencias do Espa莽o in Portugal; Aur茅lie Guilbert-Lepoutre with the Laboratoire de G茅ologie de Lyon in France; Michele Bannister with the University of Canterbury in New Zealand; and Joshua Emery and Lucas McClure with Northern Arizona University.

Researchers’ Credentials:

De Pr谩 joined 麻豆原创 FSI in 2022 as an assistant scientist. He previously spent nearly four years as a associate at FSI. De Pr谩 received his doctorate in astronomy in 2017 at the Observat贸rio Nacional do Rio de Janeiro, Brazil. He works with observational planetary sciences using several ground and space-based telescopes to study the connection between different small body populations.

Pinilla-Alonso is a professor at FSI and joined in 2015. She received her doctorate in astrophysics and planetary sciences from the Universidad de La Laguna in Spain. Pinilla-Alonso also holds a joint appointment as a professor in 麻豆原创鈥檚聽聽and has led numerous international observational campaigns in support of NASA missions such as New Horizons, OSIRIS-REx and Lucy.

Harvison recently pored through a library of infrared telescope data to analyze the spectral composition of 25 members of the Erigone family of primitive asteroids and help fill in the gaps in our understanding of the creation of our solar system.

The data on the Erigone asteroids, which are located in the main asteroid belt found between the orbits of Mars and Jupiter, was collected as part of the PRIMitive Asteroid Spectroscopic Survey (PRIMASS) project co-led by 麻豆原创 planetary scientist Noem铆 Pinilla-Alonso.

Harvison鈥檚 work, which was published recently in the journal Icarus, lays the foundation for future research, and may get scientists closer to concluding if asteroids brought water to Earth and if so, how much.

鈥淭here are theories that the Earth could have received a fraction of its water from primitive asteroids in the early Solar System,鈥� says Harvison, who is also a researcher at the . 鈥淎 big portion of these theories is understanding how these primitive asteroids were transported into Earth鈥檚 path. So, exploring primitive asteroids in the Solar System today could help paint a picture of what was going on all those years ago.鈥�

Some of these cosmic travelers, including the asteroids within the Erigone family, have hydrated silicates. The existing hydrated bodies that continue to move throughout our solar system could tell us more about those that collided with Earth.

It is one of the many outstanding questions that Harvison鈥檚 work is hoping to address.

鈥淲e mainly wanted to see if there were primitive asteroid families similar to the Erigone and Polana asteroid families,鈥� Harvison says. 鈥淲e used spectroscopy to study what kinds of minerals were on the surface to understand their composition.鈥�

From the study, Harvison and her co-authors saw that the Erigone and Polana families are different from one another聽in the near infrared but that the other primitive families have their own levels of red color in their spectral distribution along with their own unique levels of hydration.

In other words, the primitive families in the inner solar system show a variety of redness and hydration. The analysis and comparison show evidence that these families are not linked聽to the proposed Erigone-like or Polana-like groups, challenging the previously held theories as to where they fit in. Also, one particular asteroid, (52246) Donaldjohanson, seems to belong to the Erigone family based on its spectrum.

Piecing Together History

Due to the importance of understanding the nature of primitive objects, numerous spacecraft have targeted primitive asteroids, such as JAXA鈥檚 Hayabusa2 and NASA鈥檚 OSIRIS-REx, which visited, studied, and returned samples from Ryugu and Bennu, respectively.

Bennu and Ryugu prompted researchers to further study primitive asteroids and figure out where they came from, Harvison says.

Erigone was one of the final pieces of the large library of PRIMASS data that existed, but had yet to be studied, Harvison says. PRIMASS aims to understand the variety of surface properties amongst primitive collisional families in the asteroid belt and map their composition.

A collisional family of asteroids refers to a group of asteroids that are believed to have originated from the breakup of a larger parent body due to a collision. The members of a collisional family provide information about the interior of the intact body they were part of before the impact.

The PRIMASS project is characterizing the collisional families of primitive asteroids in the main belt, and particularly those that could be the origin of the primitive near-Earth asteroids such as Bennu and Ryugu.

The conclusions drawn by studying collisional families like Erigone are critical puzzle pieces in the greater endeavor of understanding the creation of our solar system.

鈥淭he larger scope was to look at primitive聽families in the inner part of the main asteroid belt, where Ryugu and Bennu are thought to have likely originated,鈥� she says. 鈥淭he聽Erigone family was the last piece of the puzzle to be placed into the PRIMASS library to provide full context on primitive asteroids in this region and allow other scientists to analyze the data.鈥�

Harvison鈥檚 research provides supplemental context for the upcoming NASA Lucy mission, which will have the eponymous spacecraft visiting (52246) Donaldjohanson in Spring 2025 before it moves on to examine eight Trojan objects (space rocks trapped in Jupiter鈥檚 orbit) in 2027 through 2033.

Looking to the Future

Study co-author M谩rio De Pr谩, an assistant scientist at FSI, served as a research assistant and Harvison鈥檚 co-supervisor. Co-author Pinilla-Alonso is Harvison鈥檚 research advisor and assisted Harvison in her research.

Pinilla-Alonso says she鈥檚 delighted to assist Harvison and see her growth.

鈥淔or me, it was a pleasure to see the process and the end result,鈥� she says. 鈥淪he contacted me early during the pandemic when we were all working at home to express her interest in pursuing a Ph.D. degree here at 麻豆原创. Here we are about three years later: she has done an awesome job and there is more to come.鈥�

Pinilla-Alonso and Harvison say they were surprised that no one had studied the spectroscopy of the Erigone family.

鈥淲hen Brittany landed on this project, we saw there was one piece of information we were missing,鈥� Pinilla-Alonso says. 鈥淧RIMASS had completed the analysis of the visible and near-infrared of all the primitive families in the inner belt but there was one missing family: Erigone. That was very important because it was the family that could give closure to learning about the inner [asteroid] belt families. Until you ask the right question or have the tools, sometimes you don鈥檛 seek that answer. But, in this case, we had the observations done and it was clear that we needed to analyze it.鈥�

The knowledge gained from studying Bennu, Ryugu, and the Erigone and Polana primitive asteroid families will serve as a springboard for future James Webb Space Telescope observations and NASA missions.

鈥淚t is very exciting times going through all of this new data with more to come with the James Webb Space Telescope,鈥� Pinilla-Alonso says. 鈥淚 really think the biggest discovery is yet to come. The data we can collect from Earth is limited. Now, we have the best tool in space to keep learning more.鈥�

Pinilla-Alonso, Harvison and other researchers at FSI are slated to begin using the JWST as early as this summer to observe Erigone and other primitive asteroids, and, over a span of about two years, evaluate the collected spectra.

Harvison maintains her enthusiasm as she looks forward to building upon her analyses and further unraveling the origins of these primitive asteroids.

鈥淭here鈥檚 this fascination when I鈥檓 looking at this data and I鈥檓 examining something that鈥檚 millions of miles away,鈥� Harvison says. 鈥淲e can look back billions of years and learn the initial structure and composition of the early solar system by聽studying the surface of these asteroids. That鈥檚 always been something that excites me.鈥�

In addition to Harvison, Pinillia-Alonso and De Pr谩, FSI colleague and head of the Planetary and Space Science Group Humberto Campins provided research support. Vania Lorenzi of Fundaci贸n Galileo Galilei and Instituto de Astrof铆sica de Canarias, David Morate of El Centro de Estudios de F铆sica del Cosmos de Aragon, Julia de Le贸n and Javier Licandro of Instituto de Astrof铆sica de Canarias and Universidad de La Laguna, Anicia Arredondo of the Southwest Research Institute also contributed to the research.

Researchers鈥� Credentials

Harvison joined 麻豆原创 in 2021 and is a graduate student working toward her doctoral degree in physics. She graduated from Northern Arizona University in 2020 with a degree in astronomy, planetary astronomy, and science.

Pinilla-Alonso is a professor at FSI and joined 麻豆原创 in 2015. She received her doctorate in astrophysics and planetary sciences from the Universidad de La Laguna in Spain. Pinilla-Alonso also holds a joint appointment as a professor in 麻豆原创鈥檚聽聽and has led numerous international observational campaigns in support of NASA missions such as New Horizons, OSIRISREx and Lucy.