1. Abstract. The James Webb Space Telescope (JWST), now in full operation, has demonstrated unprecedented sensitivity and enabling observations of objects throughout the solar system and beyond. JWST has now glimpsed at the planets and their systems revealing new insights into atmospheric composition, activity, and origin. The first 3 annual cycles of science have also included multiple programs from specific targets to larger population studies of small bodies in the asteroid belt and beyond Neptune, deciphering their composition, activity, and origin. JWST has revolutionized studies of all small bodies in the solar system with its wavelength coverage and sensitivity to measure the composition of sometimes barely active objects – even in the farthest reaches of the known solar system. The more active or larger objects can usually be resolved with flyby quality imaging to disentangle the native composition and understand the pristine nature of these objects. Additionally, the search for biosignatures and studies of ocean worlds with JWST will provide an avenue to support the detection of habitability in the solar system. All of this coupled to the new, resolved observations of disks, star formation, and exoplanets will be revolutionary in deciphering how our solar system came to be and insights into star and planet formation/evolution throughout our galaxy and beyond.
2. Background. On 25 December 2021, JWST was launched into space on an Ariane 5 rocket to L2 flawlessly, conserving fuel after trajectory adjustment and orbit insertion to operate for up to 20 years. Six months of commissioning – including optical alignment, instrument mode check out, and operations testing – led to the release of images from a perfectly aligned telescope with performance that exceeded expectations (Rigby et al. 2023; McElwain et al. 2023).
JWST was designed to address four science themes (Gardner et al. 2006): The End of the Dark Ages, The Assembly of Galaxies, The Birth of Stars and Protoplanetary Systems, and The Planetary System and the Origins of Life. While considerably challenging, especially for a large space telescope designed to peer at the faintest objects in the infant universe, JWST began observing the biggest and brightest planets in our solar system and demonstrated its incredible capability, dynamic range, and tracking accuracy (Figure 1). The first year of images and spectra towards our solar system’s planets and small bodies in the JWST field-of-regard (it cannot observe objects towards the Earth, Moon, and Sun due to the sunshield) have provided new views of these objects in the near-to-mid-infrared. Additionally, while it is generally assumed the search for “Origins of Life” with JWST is linked to habitable exoplanets – the solar system has several compelling worlds that just may be habitable as well beyond Earth.
When searching for habitability remotely (either in the solar system or towards other planetary systems), the accurate characterization of several volatile species (e.g., water, carbon dioxide, methane, ammonia, etc.) is critical as the primary building blocks of larger complex molecules but also key for life as we know it. Fortunately, these molecules have distinct and prominent infrared signatures that fall within the range of JWST. Understanding the distribution and origin of volatile species throughout the solar system and what processes may influence them (geologic or evolutionary, for example) is critical to piece together how the right ingredients came to Earth and contributed to our habitability here. This is also essential for understanding the processes occurring in other planetary systems and how the volatile chemistry will contribute to planet formation. Finally, understanding the ubiquitous nature of volatile chemistry and the possible inheritance of these volatiles from the interstellar medium, protostars, planetary disks, to planetary systems will guide our searches for other worlds similar to Earth or perhaps other extreme objects such as ocean worlds like Europa, Enceladus, or Titan.
The story of volatiles and their history in the solar system or even an origin prior to planet formation is best understood through isotopic signatures and detailed compositional studies. JWST’s spectral coverage, unique instrumentation (including integral-field-unit, or IFU, spectrometers that offer spectral maps of molecules), unprecedented sensitivity, and resolution provides a powerhouse of combined methods to help disentangle the pristine nature of volatiles throughout the solar system from small bodies to planetary atmospheres, and ocean worlds. Figure 2 provides a simulated perspective of these tracers as JWST can measure them spectroscopically (adapted from Villanueva and Milam, 2024).
3. Small Bodies. JWST’s incredible sensitivity and spectral coverage is well-suited for detailed compositional studies of small bodies – especially those in the outer solar system. All families of small bodies are being observed including near-Earth objects (NEOs), main-belt asteroids and comets, centaurs, comets, and trans-Neptunian objects (TNOs), and the science returned to date is revealing new insights into the relics of our solar system’s formation.
The sensitivity of JWST is giving us access to some of the mysteries across our solar system. A notable finding was the detection of water vapor in a main belt comet, 238P/Read (Kelley et al., 2023). These active bodies in the asteroids have perplexed astronomers since their discovery in 2006 (Hsieh and Jewitt, 2006) and have eluded the detection of volatiles with attempts made with some of the largest telescopes in the world – until JWST. This finding is incredibly significant by 1) demonstrating the power of JWST to detect extremely low abundances of volatiles, 2) resolving the driving activity phenomenon of these bodies in the asteroid belt, and 3) identifying a presence of volatile material that is currently unrepresented in comets and the meteoritic record. This final point is critical for the further understanding of the early solar system’s volatile composition, distribution, and evolution (Kelley et al., 2023). This initial finding has led to further studies of fainter and fainter targets (both near and far) with JWST to study their composition, activity, and origin.
The diversity of small bodies across the solar system is also being revealed in surprising ways and demonstrated by representative spectra of 3 targets observed with JWST in Figure 3 – a comet, C/2022 E3 (ZTF) (Milam et al., in preparation); a centaur, 39P/Oterma (Harrington Pinto et al., 2023), and a TNO, Eris (Grundy et al., 2024). Comet spectra from JWST across the near and mid-infrared have shown the wealth of molecular outgassing from sublimating ices in these bodies as they journey through the inner solar system, across major ice-lines, in their orbits. JWST’s spectroscopic capabilities provide fundamental insights on the volatile composition, isotope and cosmogonic ratios (e.g., 12CO2/13CO2 – see inset in Figure 3, ortho-to-para water abundance ratios), as well as insights into the heterogeneous nature of these icy relics with the 2-D images of each molecular species in the IFU (Milam et al., in preparation). Moving toward the outer solar system and peering at bodies that reside at distance around the giant planets, to a population known as Centaurs – objects transitioning from TNO to Jupiter-family comet. These objects reside past the water-ice sublimation distance in the solar system, but still have some activity. Like the main belt comet, 238P, the opportunity to study these “barely active” objects with the powerful JWST was a must. The first looks have been exciting, showing for the first-time carbon dioxide (CO2) gas-phase emission. This is complemented by the water-ice absorption features that are consistent with other comets (Harrington Pinto et al., 2023). The centaur data are clearly more evolved with less ice than the TNO spectra shown in Figure 3 of Eris. Eris is a large TNO (comparable in size to Pluto) and has an extensive amount of methane (CH4) ice across its surface as shown by the broad absorption peaks across the spectrum, as well as some contribution of N2-ice (Grundy et al., 2024). The surprise in these data was the strong absorption features of deuterated methane (CH3D). Analysis of these observations yield an isotope ratio of D/H ~2.5×10-4, a value inconsistent with primordial D/H abundance estimates at ~2×10-3 and alluding to some endogenic activity from a rocky core (Glein et al., 2024).
The diversity and new evidence for activity, processes, and chemistry in these icy relics have complicated the story for understanding the volatile inventory of our solar system upon formation, but also providing critical insights into the true tracers of our molecular origins.
4. Ocean Worlds. The search for habitability in our solar system and beyond is focused on terrestrial planets with atmospheres and the presence of water, or in bodies known as ocean worlds that may or may not have an atmosphere but do have liquid on or beneath the surface with an internal or external energy source that could support a habitable environment. Different processes may leave molecular evidence that JWST is privy to by studying plumes of gas spewing from the subsurface, deposits of ice or minerals on the surface, or even variables in an atmosphere that suggest activity. JWST is observing a number of these objects and revealing details on composition and activity that even dedicated spacecraft to these bodies in the solar system had not identified. One such example is Saturn’s moon, Enceladus. While a plume of water-rich gas was identified and studied with the Cassini mission, JWST measured the extent of the water vapor coming from this moon and its contribution to the torus and E ring (Villanueva et al., 2023a). This quick glimpse at Saturn’s moon did not detect other species, though deeper searches with JWST are now underway.
Another world of keen interest with a known subsurface ocean is the Galilean moon, Europa. This moon has an elusive plume of water vapor, discovered by Hubble (Roth et al., 2014), though not confirmed with many other attempts at various facilities. The power of JWST would readily reveal plumes, if present, and provide insights across the surface if a subsurface plume re-deposited volatile material on the surface as a volcano does with lava. While a plume of gas was not confirmed with a first glimpse with JWST, multiple bands of CO2 ice were detected and mapped across the disk of the moon (Villanueva et al., 2023b; Trumbo and Brown 2023) – see Figure 4. It was determined that the CO2 is concentrated in a region that has no cratering, likely regenerated from subsurface geologic activity where material is transported to the surface.
JWST is also peering at other ocean worlds and revealing intriguing chemistry and dynamics that had not been observed before. The volatile content of these bodies provides insights into the primordial conditions from which they were formed.
5. Concluding Remarks. Since its launch in late 2021, JWST has already provided fundamental insight into the composition and dynamics of planetary/satellite atmospheres/exospheres and rings as well as the composition of small bodies, the distribution of volatiles and processed materials across the different reservoirs, and new insights into the formation of the solar system. The question of habitability throughout our solar system is of particular interest and the focus of many upcoming planetary missions – JWST is offering preliminary data to help guide those missions and complement their suite of instrumentation. More importantly, new phenomena and questions are already emerging, revolutionizing this area of research. The nominal launch and efficient operations in place ensure a JWST science mission lifetime of up to 20 years, enabling new discoveries and exploration for future generations.
Acknowledgements. SNM acknowledges support from the JWST Project at NASA Goddard Space Flight Center and the NASA JWST Interdisciplinary Scientist grant 21-SMDSS21-0013. Special thanks to G. Villanueva, O. Harrington Pinto, W. Grundy, and N. Roth for data to be incorporated in figures.
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