<h3>Discovering Light Hydrocarbons and Complex Molecules: Insights from the James Webb Space Telescope</h3>
<img src=”sedna-planet-outer-solar-system.jpg” alt=”Artist’s Visualization of Planet-like Object ‘Sedna’ in Outer Solar System” title=”Credit: NASA/JPL-Caltech” />
Using the James Webb Space Telescope (JWST), astronomers made groundbreaking observations of three dwarf planets in the Kuiper Belt, unveiling the presence of light hydrocarbons and complex organic molecules. These remarkable findings enhance our comprehension of objects within the outer regions of the Solar System while shedding light on the JWST’s remarkable capabilities in space exploration.
The Kuiper Belt, an extensive area at the periphery of our Solar System, teems with countless icy objects, providing a plethora of scientific discoveries. The detection and characterization of Kuiper Belt Objects (KBOs), also known as Trans-Neptunian Objects (TNOs), have revolutionized our understanding of the Solar System’s history. The arrangement of KBOs reflects gravitational currents that have shaped our Solar System and illuminate a dynamic narrative of planetary migration. Scientists have been eagerly anticipating the opportunity to closely examine KBOs since the late 20th century, enabling a deeper understanding of their orbits and composition.
A core objective of the James Webb Space Telescope (JWST) is the study of celestial bodies within the outer reaches of the Solar System. Scientists utilized data collected by Webb’s Near-Infrared Spectrometer (NIRSpec) to investigate three dwarf planets in the Kuiper Belt: Sedna, Gonggong, and Quaoar. These observations unveiled intriguing aspects of their respective orbits and composition, including the presence of light hydrocarbons and complex organic molecules believed to have formed through methane irradiation.
Leading this research is Joshua Emery, a Professor of Astronomy and Planetary Sciences at Northern Arizona University, in collaboration with researchers from NASA’s Goddard Space Flight Center (GSFC), the Institut d’Astrophysique Spatiale (Université Paris-Saclay), the Pinhead Institute, the Florida Space Institute (University of Central Florida), the Lowell Observatory, the Southwest Research Institute (SwRI), the Space Telescope Science Institute (STScI), American University, and Cornell University. A preprint of their findings has been published online and is currently undergoing review for potential publication in Icarus, a renowned scientific journal.
While our knowledge of the Trans-Neptunian Region and the Kuiper Belt remains limited despite significant advancements in astronomy and robotic exploration, the launch of the JWST has been awaited with great anticipation by astronomers. Apart from the study of exoplanets and the earliest galaxies in the Universe, the JWST’s powerful infrared imaging capabilities have been directed towards our cosmic neighborhood, capturing new images of Mars, Jupiter, and its largest moons. Emery and his team analyzed near-infrared data obtained by the JWST, focusing on three planetoids in the Kuiper Belt: Sedna, Gonggong, and Quaoar. These celestial bodies have a diameter of approximately 1,000 km (620 mi), categorizing them as Dwarf Planets according to the International Astronomical Union (IAU).
Sedna, Gonggong, and Quaoar are particularly fascinating to astronomers due to their size, orbits, and composition, as Emery explained in an email interview with Universe Today. While other Trans-Neptunian objects like Pluto, Eris, Haumea, and Makemake have retained volatile ices on their surfaces (such as nitrogen and methane), Sedna, Gonggong, and Quaoar present a unique opportunity to investigate if they exhibit similar characteristics:
“Previous work has shown that they may be able to. While all being roughly similar sizes, their orbits are distinct. Sedna is an inner Oort Cloud object with a perihelion of 76 AU and aphelion of nearly 1,000 AU, Gonggong is in a very elliptical orbit also, with perihelion of 33 AU and aphelion ~100 AU, and Quaoar is in a relatively circular orbit near 43 AU. These orbits place the bodies in different temperature regimes and different irradiation environments (Sedna, for instance, spends most of its time outside the Sun’s heliosphere). We wanted to investigate how those different orbits could affect the surfaces. There are also other interesting ices and complex organics on the surfaces.”
Using data from Webb’s NIRSpec instrument, the team examined all three bodies at low-resolution prism mode, covering wavelengths ranging from 0.7 to 5.2 micrometers (µm) within the near-infrared spectrum. Medium-resolution grating observations were also conducted on Quaoar, spanning wavelengths from 0.97 to 3.16 ?m at ten times the spectral resolution. The resulting spectra offered intriguing insights into these TNOs and their surface compositions. Emery shared the following discoveries:
“We found abundant ethane (C2H6) on all three bodies, most prominently on Sedna. Sedna also shows acetylene (C2H2) and ethylene (C2H4). The abundances correlate with the orbit (most on Sedna, less on Gonggong, least on Quaoar), which is consistent with relative temperatures and irradiation environments. These molecules are direct irradiation products of methane (CH4). If ethane (or the others) had been on the surfaces for a long time, they would have been converted to even more complex molecules by irradiation. Since we still see them, we suspect that methane (CH4) must be resupplied to the surfaces fairly regularly.”
These findings align with recent studies led by Dr. Will Grundy, an astronomer at the Lowell Observatory and a co-investigator on NASA’s New Horizons mission, and Chris Glein, a planetary scientist and geochemist at the SwRI. These studies analyzed deuterium/hydrogen (D/H) ratios in methane on Eris and Makemake and concluded that the observed methane was not primordial. Instead, they postulated that methane undergoes internal processing within these dwarf planets before surfacing. Emery suggests that a similar process may occur on Sedna, Gonggong, and Quaoar:
“We suggest the same may be true for Sedna, Gonggong, and Quaoar. We also see that the spectra of Sedna, Gonggong, and Quaoar are distinct from those of smaller KBOs. There were talks at two recent conferences that showed JWST data of smaller KBOs cluster into three groups, none of which look like Sedna, Gonggong, and Quaoar. That result is consistent with our three larger bodies having a different geothermal history.”
These findings have significant implications for the study of KBOs, TNOs, and other celestial bodies populating the outer Solar System. They provide new insights into the formation of objects beyond the Frost Line in planetary systems, which refers to the boundary beyond which volatile compounds freeze solidly. In our Solar System, this line corresponds to the nitrogen line, where bodies retain ample amounts of volatiles with very low freezing points (such as nitrogen, methane, and ammonia). Emery explains that these observations also shed light on the type of evolutionary processes occurring in this region:
“The primary implication may be finding the size at which KBOs have become warm enough for interior reprocessing of primordial ices, perhaps even differentiation. We should also be able to use these spectra to better understand irradiation processing of surface ices in the outer Solar System. And future studies will also be able to look in more detail at volatile stability and the possibility for atmospheres on these bodies over any parts of their orbits.”
These findings underscore the impressive capabilities of the James Webb Space Telescope, which has consistently delivered groundbreaking data ever since it became operational in early 2021. Additionally, they remind us that the JWST not only enables us to explore distant planets, galaxies, and the vast structures within the Universe but also offers profound insights into our own cosmic neighborhood.
“The JWST data are fantastic,” Emery affirms. “They enabled us to obtain spectra at longer wavelengths than what is achievable from the ground, allowing us to detect these ices. Typically, when observing in a new wavelength range, the initial data…”
