Water vaporization on Ceres
Abstract
We present long-exposure IUE spectra of the region around Ceres in which one might find escaping OH resulting from the photodissociation of atmospheric water vapor. An exposure off the southern limb of Ceres before perihelion shows no evidence for OH emission. An exposure off the northern limb of Ceres after perihelion shows a statistically significant detection of OH. The amount of OH is consistent with, among many possibilities, a polar cap which is replenished during winter by subsurface percolation as discussed by Fanale and Salvail (1989, Icarus 82, 97–110) and which dissipates in summer.
References (11)
- F.P. Fanale et al.
The water regime of Asteroid (1) Ceres
Icarus
(1989) - W.-H. Ip
On a hot oxygen carona of Mars
Icarus
(1988) - L.A. Lebofsky et al.
2.7–4.1 μm Spectrophotometry of Icy Satellites of Saturn and Jupiter
Icarus
(1985) - L.A. Lebofsky et al.
The 1.7- to 4.2-μm spectrum of Asteroid 1 Ceres: Evidence for structural water in clay minerals
Icarus
(1981) - R.L. Millis et al.
The Size, Shape, Density, and Albedo of Ceres from Its Occultation of BD + 8°471
Icarus
(1987)
Cited by (112)
Ceres—A volatile-rich dwarf planet in the asteroid belt
2023, Ices in the Solar-System: A Volatile-Driven Journey from the Inner Solar System to its Far ReachesWell before the arrival of the Dawn mission in 2015, the dwarf planet Ceres, the largest object in the main asteroid belt, was known to be water-rich and suspected to host water-driven geophysical and geological processes. Dawn confirmed the significant role of water in shaping the chemical and physical evolution of Ceres and found evidence that it accreted organics and volatiles such as carbon dioxide and ammonia. Water-rock interaction led to chemical fractionation and the production of brines (salt-rich liquid) containing significant carbonate and bicarbonate, as well as ammonium and chlorides. Local enhancements in water ice and other salt deposits suggest that some amount of ongoing volatile exposure and loss is occurring in the present day from likely extensive subsurface layers of material. Although the Dawn spacecraft ran out of fuel in 2018 and remains silently in a ~50-year stable orbit, the analysis of the extensive dataset returned by the mission keeps expanding our understanding of this large, water-rich body and has fostered in situ and sample return mission concepts about investigating Ceres’ past and present habitability potential that may be considered for flight in the next decade.
Exosphere-mediated migration of volatile species on airless bodies across the solar system
2022, IcarusSurface-bound exospheres facilitate volatile migration across the surfaces of nearly airless bodies. However, such transport requires that the body can both form and retain an exosphere. To form a sublimation exosphere requires the surface of a body to be sufficiently warm for surface volatiles to sublime; to retain an exosphere, the ballistic escape and photodestruction rates and other loss mechanisms must be sufficiently low. Here we construct a simple free molecular model of exospheres formed by volatile desorption or sublimation. We consider the conditions for forming and retaining exospheres for common volatile species across the Solar System, and explore how three processes (desorption/sublimation, ballistic loss, and photodestruction) shape exospheric dynamics on airless bodies. Our model finds that the CO2 exosphere of Callisto is much too dense to be sustained by impact-delivered volatiles, but could be maintained by only ~7 ha (~0.07 km2) of exposed CO2 ice distributed across Callisto (and refreshed through mass wasting). We use our model to predict the peak surface locations of Callisto's CO2 exosphere along with other Galilean moons, which could be tested by JUICE observations. Our model finds that to maintain Iapetus' two-tone appearance, its dark Cassini Regio likely has unresolved exposures of water ice, perhaps in sub-resolution impact craters, that amount to up to approximately ~0.06% of its surface. In the Uranian system, we find that the CO2 deposits on Ariel, Umbriel, Titania, and Oberon are unlikely to have been delivered via impacts, but are consistent with both a magnetospheric origin, (as has been previously suggested) or sourced endogenously. We suggest that the leading/trailing CO2 asymmetries on these moons could result from exosphere-mediated volatile transport, and may be a seasonal equinox feature that could be largely erased by pole-to-pole volatile migration during the Uranian solstices. We calculate that ~2.4–6.4 mm thick layer of CO2 (depending the moon) could migrate about the surface of Uranus' large moons during a seasonal cycle. Our model also confirms that water migration to Mercury's polar cold traps is inefficient without self-shield against photodestroying UV light, and that Callisto's bright spires could be formed/maintained by exospherically deposited H2O.
Ceres, a wet planet: The view after Dawn
2022, GeochemistryCeres, a nearly 1000-km diameter body located in the Solar System’s main asteroid belt, has been classified under many categories: planet, comet, asteroid, minor planet and, presently, dwarf planet. No matter what the designation, Ceres has experienced major planetary processes. Its evolution has been controlled by water, making it a most unusual, interesting and accessible inner Solar System object that can inform the evolution of outer Solar System moons and other dwarf planets. Early telescopic observations suggested a hydroxylated mineralogy similar to carbonaceous chondrite meteorites and a size and mass indicating a bulk density that implied a water content of 17−27 wt%. Thermodynamic modeling of Ceres’ evolution indicated that thermal aqueous evolution likely occurred. The Dawn Mission produced a huge increase in our understanding of Ceres, confirming but vastly extending the early knowledge. Dawn, carrying multispectral cameras, a visible-infrared imaging spectrometer and a nuclear spectrometer, orbited Ceres between 2015–2018 (after orbiting Vesta) at a number of different altitudes, ultimately reaching 35 km from the surface at periapsis. Observations of almost the entire surface and gravity field mapping revealed multiple geological and internal features attributed to the effects of water. The surface displays cryovolcanic-like and flow structures, exposed phyllosilicates, carbonates, evaporites and water ice. The subsurface shows partial differentiation, decreasing viscosity with depth, and lateral density heterogeneity. Ceres appears to be geologically active today and possesses liquid water/brine pockets or even an extended liquid layer in the interior, confirming an “Ocean World” designation in today’s vernacular.
The case for a Themis asteroid family spacecraft mission
2022, Planetary and Space ScienceThe last decade has highlighted the importance of icy asteroids as likely outer-solar-system planetesimals that brought organics and ices to the inner solar system. Better characterizing the relationship between these objects and other water-rich bodies throughout the solar system and their evolution as potential sources of organics has broad-ranging implications. Additionally, characterizing ice-rich bodies is important for understanding the evolution and diversity of Ocean Worlds. Observations and modeling have suggested that the Themis asteroid family likely represents the fragments of an icy protoplanet originally similar in size to (10) Hygeia (∼444 km), which was broken apart by a catastrophic collision and with (24) Themis possibly representing its core. While extensive observations have been made of the icy asteroid (1) Ceres, exploring the deep interior structure and processes is difficult when observing an intact planetary body. Thus, the many objects in the Themis family provide an opportunity to observe an interior cross-section of one of these protoplanetary objects. The Themis family contains a variety of members, including multiple Main Belt Comets (e.g., 133P/Elst-Pizarro) for which comet-like dust ejection (consistent with being driven by sublimation of volatile material) has been observed. In this paper, we present the science case for why the exploration of the Themis family is key to understanding icy objects in the solar system, and present three design-referenced mission architectures that would be plausible under the NASA Discovery mission cost cap that would address key science objectives pertaining to icy asteroids.
Cryovolcanism
2021, Planetary Volcanism across the Solar SystemCryovolcanism has been either observed on or suspected for numerous icy bodies across the Solar System, most notably Saturn’s tiny moon Enceladus, where jets of water vapor and other constituents are spewed into space from giant fractures near the South Pole. In this chapter, we review cryomagmatism and cryovolcanism, which are the subsurface and surface processes, respectively, resulting from the mobilization and migration of fluids generated in the interiors of icy bodies. Although these phenomena have no direct equivalents on Earth, they are important processes in the icy Solar System, and we can draw inferences as to how they operate from silicate volcanism in the inner Solar System. We discuss mechanisms of cryomagmatism and cryovolcanism, the possible compositions of cryomagmas, and the observational evidence found so far on extraterrestrial bodies, which range from plumes to geological features interpreted as cryovolcanic in origin.
Ceres and Pluto
2020, Encyclopedia of Geology: Volume 1-6, Second EditionThe first detailed investigations of the dwarf planets, Ceres and Pluto, occurred in the same year, 2015. That year the Dawn spacecraft entered orbit around Ceres and the New Horizons spacecraft flew past Pluto. These missions provided images at an unprecedented resolution to reveal the complex geology and composition of their surfaces. These data have revolutionized the way we think about sub-planetary worlds. Despite their different locations in the solar system, Ceres in the Main Belt (~ 2.8 AU) and Pluto in the Kuiper Belt (~ 40 AU) both bodies revealed unexpected signs of current or geologically recent activity. Ceres has carbonate-rich features including the 4-km tall Ahuna Mons that may have been emplaced in the last few 100 s Myrs, and Pluto shows current evidence of convection in its large glacial basin filled with volatile ices. Also, both Ceres and Pluto show evidence of a past or current subsurface ocean. The interior structure of Ceres was investigated by Doppler tracking as Dawn orbited Ceres. In contrast, Pluto's bulk density is derived from the orbit of its satellites. The interior structure of Pluto is inferred by tectonic features and the location of a large basin which is located along the tidal axis of Pluto and its large satellite, Charon.