Astronomers using the James Webb Space Telescope to observe three dwarf planets in the Kuiper Belt discovered light hydrocarbons and complex molecules. These discoveries enhance our understanding of objects in the outer solar system and highlight the capabilities of the James Webb Space Telescope for space exploration.
In this artist's vision, the newly discovered planet-like object named Sedna is located on the outer edge of the known solar system. Image source: NASA/JPL-Caltech
The Kuiper Belt is a vast area at the edge of the solar system, home to countless icy objects, and a treasure trove of scientific discoveries. The detection and characterization of Kuiper Belt Objects (KBOs), sometimes called Trans-Neptunian Objects (TNOs), has given new insights into the history of the solar system. The arrangement of Kuiper Belt objects is an indicator of the gravitational flows that shape the solar system and reveal the dynamic history of planetary migration. Since the late 20th century, scientists have been eager to take a closer look at KBOs to learn more about their orbits and composition.
Observations from the James Webb Space Telescope
Studying objects outside our solar system is one of the many goals of the James Webb Space Telescope (JWST). Using data from the Webb Telescope's Near Infrared Spectrometer (NIRSpec), an international team of astronomers observed three dwarf planets in the Kuiper Belt: Sedna, Gonggong, and Quaoar. These observations revealed some interesting phenomena in their respective orbits and compositions, including light hydrocarbons and complex organic molecules believed to be products of methane irradiation.
The research was led by Joshua Emery, a professor of astronomy and planetary science at Northern Arizona University. Researchers from NASA's Goddard Space Flight Center (GSFC), the Institut d'Astrophysique Spatiale of Paris-Saclay University, 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 also participated in the study. A preprint of their paper has been published online and is under review by Icarus.
Since its last flyby of the Kuiper Belt object Arrokoth, the New Horizons mission has been exploring Kuiper Belt objects and conducting heliospheric and astrophysical observations. Source: NASA/JHUAPL/SwRI//RomanTkachenko
History of Kuiper Belt Exploration
Despite great advances in astronomy and robotic detectors, our knowledge of the Trans-Neptune Region and the Kuiper Belt remains limited. To date, the only mission to study Uranus, Neptune and their major moons is the Voyager 2 mission, which flew by these ice giants in 1986 and 1989 respectively. In addition, New Horizons was the first spacecraft to study Pluto and its moons (July 2015) and the only spacecraft to encounter an object in the Kuiper Belt. It flew by the Kuiper object named "Arokos" on January 1, 2019.
What astronomers are expecting from JWST
This is one of the many reasons astronomers eagerly await the launch of JWST. In addition to studying exoplanets and the earliest galaxies in the universe, its powerful infrared imaging capabilities are also being directed into our backyard, revealing new images of Mars, Jupiter, and their largest moons. In the study, Emery and his colleagues referred to near-infrared data obtained by Webb of three Kuiper belt planets - Sedna, Gonggong and Quaoar. These objects are about 1,000 kilometers (620 miles) across and fall into the International Astronomical Union's (IAU) dwarf planet category.
Insights about dwarf planets
Astronomers are of particular interest in these objects because of their size, orbit and composition. Other trans-Neptunian objects, such as Pluto, Eris, Haumea, etc., all retain volatile ices (nitrogen, methane, etc.) on their surfaces. The only exception is Haumea, which lost its volatile material in a giant impact (apparently). Astronomers therefore want to observe whether similar volatiles are present on the surfaces of Sedna, Gonggong and Quiall:
"Previous work suggests they might. Although they are roughly the same size, their orbits are very different. Sedna is an inner Oort cloud object, with perihelion of 76 AU and aphelion of nearly 1000 AU; Gonggong's orbit is also very elliptical, with perihelion of 33 AU and aphelion of about 100 AU; "Quior's orbit is relatively circular, close to 43 AU. These orbits expose the object to different temperature regimes and different irradiation environments (for example, Sedna spends most of its time outside the Sun's heliosphere). We wanted to study how these different orbits would affect the surface of the object."
An image from one of two PRISM grating observations of Sedna, Gonggong and Quiall. Source: Emery, J.P. et al. (2023)
Using data from the Webb Near Infrared Telescope (NIRSpec), the team observed the three objects in low-resolution prism mode, with wavelengths ranging from 0.7 microns to 5.2 microns - placing them all in the near-infrared spectrum. In addition, they made additional observations of Quaoar at wavelengths from 0.97 to 3.16 microns using a medium-resolution grating, which provides ten times the spectral resolution. The resulting spectra revealed some interesting things about the composition of these dust particles and surfaces, Emery said:
"We found abundant ethane (C2H6) on all three objects, with Sedna being the most prominent. Sedna also shows acetylene (C2H2) and ethylene (C2H4). The abundance is orbit-dependent (most on Sedna, less on Gongong, least on Quiol), which correlates with relative temperature and irradiation rings "These molecules are the direct irradiation products of methane (CH4). If ethane (or other substances) are present on the surface for a long time, they will be converted into more complex molecules under irradiation, and since we can still see them, we suspect that methane (CH4) must be replenished on the surface regularly."
These findings are consistent with findings in two recent studies led by Dr. Will Grundy, an astronomer at Lowell Observatory and co-investigator of NASA's New Horizons mission, and Chris Glein, a planetary scientist and geochemist at the Swiss Academy of Sciences. In both studies, Grandi, Glien and their colleagues measured the deuterium/hydrogen (D/H) ratio in methane on Eris and Makmak and concluded that the methane was not pristine. Instead, they believe these ratios are the result of methane being transported to the surface after being processed within it.
"We think the same may be true for Sedna, Gonggong and Quiall," Emery said. "We also found that the spectra of Sedna, Gongong and Quiall are very different from those of the smaller KBOs. At the two most recent meetings, JWST data showed that the smaller KBOs fell into three groups, none of which looked like these three, a result that is consistent with our three larger objects having different geothermal histories."
The eight largest NEOs compared to Earth (all to scale). Image source: NASA/Lexicon
Impact of research results
These findings could have major implications for the study of KBOs, TNOs and other objects outside the solar system. This includes new insights into the formation of objects in planetary systems beyond the frost line, the boundary where volatile compounds freeze solid. In our solar system, the trans-Neptunian region corresponds to the nitrogen line, where objects would retain large amounts of volatile materials with extremely low freezing points (i.e., nitrogen, methane, and ammonia). Emery said the findings also demonstrate what type of evolutionary process objects in this region are undergoing:
"The main impact could be to find the size of KBOs at which they have become warm enough to allow internal reprocessing and even differentiation of the original ice. We can also use these spectra to better understand the irradiation processing of ice on the outer surface of the solar system. Future studies will also be able to observe in more detail the volatile stability and atmosphere potential of these objects in any part of their orbits."
The results of this study also demonstrate the capabilities of JWST, which has proven its worth many times since it became operational early last year. They also remind us that in addition to new insights and breakthroughs into distant planets, galaxies, and the large-scale structure of the universe, Webb can also reveal things about our little corner of the universe.
"The JWST data are fantastic," Emery added. "They allow us to obtain a spectrum with longer wavelengths than we can get on the ground, allowing us to detect these ices." Often, when making observations in a new wavelength range, the quality of the initial data can be poor. Not only does JWST open up a new wavelength range, it also provides high-quality data that is sensitive to a range of materials on the outer surface of the solar system. "
Adapted from an article originally published on Universe Today.