The Uranian moon Ariel exhibits a diversity of geologically young landforms, with a surface composition rich in CO2 ice. The origin of CO2 and other species, however, remains uncertain. We report ...observations of Ariel’s leading and trailing hemispheres, collected with NIRSpec (2.87–5.10 μm) on the James Webb Space Telescope. These data shed new light on Ariel's spectral properties, revealing a double-lobed CO2 ice scattering peak centered near 4.20 and 4.25 μm, with the 4.25 μm lobe possibly representing the largest CO2 Fresnel peak yet observed in the solar system. A prominent 4.38 μm 13CO2 ice feature is also present, as is a 4.90 μm band that results from 12CO2 ice. The spectra reveal a 4.67 μm 12CO ice band and a broad 4.02 μm band that might result from carbonate minerals. The data confirm that features associated with CO2 and CO are notably stronger on Ariel’s trailing hemisphere compared to its leading hemisphere. We compared the detected CO2 features to synthetic spectra of CO2 ice and mixtures of CO2 with CO, H2O, and amorphous carbon, finding that CO2 could be concentrated in deposits thicker than ∼10 mm on Ariel’s trailing hemisphere. Comparison to laboratory data indicates that CO is likely mixed with CO2. The evidence for thick CO2 ice deposits and the possible presence of carbonates on both hemispheres suggests that some carbon oxides could be sourced from Ariel’s interior, with their surface distributions modified by charged particle bombardment, sublimation, and seasonal migration of CO and CO2 from high to low latitudes.
Pluto’s surface is geologically complex because of volatile ices that are mobile on seasonal and longer time scales. Here we analyzed New Horizons LEISA spectral data to globally map the nitrogen ...ice, including nitrogen with methane diluted in it. Our goal was to learn about the seasonal processes influencing ice redistribution, to calculate the globally averaged energy balance, and to place a lower limit on Pluto’s N2 inventory. We present the average latitudinal distribution of nitrogen and investigate the relationship between its distribution and topography on Pluto by using maps that include the shifted bands of methane in solid solution with nitrogen (which are much stronger than the 2.15-μm nitrogen band) to more completely map the distribution of the nitrogen ice. We find that the global average bolometric albedo is 0.83±0.11, similar to that inferred for Triton, and that a significant fraction of Pluto’s N2 is stored in Sputnik Planitia. We also used the encounter-hemisphere distribution of nitrogen ice to infer the latitudinal distribution of nitrogen over the rest of Pluto, allowing us to calculate the global energy balance. Under the assumption that Pluto’s nitrogen-dominated 11.5μbar atmosphere is in vapor pressure equilibrium with the nitrogen ice, the ice temperature is 36.93±0.10 K, as measured by New Horizons’ REX instrument. Combined with our global energy balance calculation, this implies that the average bolometric emissivity of Pluto’s nitrogen ice is probably in the range 0.47–0.72. This is consistent with the low emissivities estimated for Triton based on Voyager results, and may have implications for Pluto’s atmospheric seasonal variations, as discussed below. The global pattern of volatile transport at the time of the encounter was from north to south, and the transition between condensation and sublimation within Sputnik Planitia is correlated with changes in the grain size and CH4 concentration derived from the spectral maps. The low emissivity of Pluto’s N2 ice suggests that Pluto’s atmosphere may undergo an extended period of constant pressure even as Pluto recedes from the Sun in its orbit.
•Most of Pluto’s nitrogen ice is stored in Sputnik Planitia.•Nitrogen ice is more abundant at lower elevations on Pluto.•Pluto’s bolometric albedo and emissivity are both similar to the icy moon Triton.•Globally, nitrogen is currently moving from north to south on Pluto.•Pluto’s atmosphere may have a period of constant pressure while further from the Sun.
We observed Io with the James Webb Space Telescope (JWST) while the satellite was in eclipse, and detected thermal emission from several volcanoes. The data were taken as part of our JWST‐ERS program ...#1373 on 15 November 2022. Kanehekili Fluctus was exceptionally bright, and Loki Patera had most likely entered a new brightening phase. Spectra were taken with NIRSpec/IFU at a resolving power R ≈ 2,700 between 1.65 and 5.3 µm. The spectra were matched by a combination of blackbody curves that showed that the highest temperature, ∼1,200 K, for Kanehekili Fluctus originated from an area ∼0.25 km2 in size, and for Loki Patera this high temperature was confined to an area of ∼0.06 km2. Lower temperatures, down to 300 K, cover areas of ∼2,000 km2 for Kanehekili Fluctus, and ∼5,000 km2 for Loki Patera. We further detected the a1Δ ⇒ X3Σ− 1.707 µm rovibronic forbidden SO emission band complex over the southern hemisphere, which peaked at the location of Kanehekili Fluctus. This is the first time this emission has been seen above an active volcano, and suggests that the origin of such emissions is ejection of SO molecules directly from the vent in an excited state, after having been equilibrated at temperatures of ∼1,500 K below the surface, as was previously hypothesized.
Plain Language Summary
We observed Io with JWST in November 2022 while the satellite was in Jupiter's shadow, and glowing volcanoes show up without being (partially) obscured by reflected sunlight. We detected the volcanoes Loki Patera and Kanehekili Fluctus; the latter was exceptionally bright, and Loki Patera had likely entered a new brightening phase. Both volcanoes show erupting lavas at temperatures of at least 1,200 K, originating at a vent of ∼0.25 km2 in size for Kanehekili Fluctus and <0.1 km2 for Loki Patera. In addition to lava, Kanehekili Fluctus spews out gases, and we detected, for the first time, SO emission at 1.707 μm right over the volcano. This is the first time this emission has been seen above an active volcano, and suggests that such emissions are produced by SO molecules immediately upon leaving the vent.
Key Points
James Webb Space Telescope observations detected an energetic eruption at Kanehekili Fluctus, and a new brightening event at Loki Patera
The erupting lavas have a temperature of at least 1,200 K over an area of ∼0.25 km2 or less
We detected, for the first time, a clear association of the 1.707 micron forbidden SO emissions with an active volcano
Abstract The Didymos binary asteroid was the target of the Double Asteroid Redirection Test (DART) mission, which intentionally impacted Dimorphos, the smaller member of the binary system. We used ...the Near-Infrared Spectrograph and Mid-Infrared Instrument instruments on JWST to measure the 0.6–5 and 5–20 μ m spectra of Didymos approximately two months after the DART impact. These observations confirm that Didymos belongs to the S asteroid class and is most consistent with LL chondrite composition, as was previously determined from its 0.6–2.5 μ m reflectance spectrum. Measurements at wavelengths >2.5 μ m show Didymos to have thermal properties typical for an S-complex asteroid of its size and to be lacking absorptions deeper than ∼2% due to OH or H 2 O. Didymos’ mid-infrared emissivity spectrum is within the range of what has been measured on S-complex asteroids observed with the Spitzer Space Telescope and is most consistent with emission from small (<25 μ m) surface particles. We conclude that the observed reflectance and physical properties make the Didymos system a good proxy for the type of ordinary chondrite asteroids that cross near-Earth space, and a good representative of likely future impactors.
JWST/NIRSpec Prospects on Transneptunian Objects Métayer, Robin; Guilbert-Lepoutre, Aurélie; Ferruit, Pierre ...
Frontiers in astronomy and space sciences,
02/2019, Letnik:
6, Številka:
7
Journal Article
Recenzirano
Odprti dostop
The transneptunian region has proven to be a valuable probe to test models of the formation and evolution of the solar system. To further advance our current knowledge of these early stages requires ...an increased knowledge of the physical properties of Transneptunian Objects (TNOs). Colors and albedos have been the best way so far to classify and study the surface properties of a large number TNOs. However, they only provide a limited fraction of the compositional information, required for understanding the physical and chemical processes to which these objects have been exposed since their formation. This can be better achieved by near-infrared (NIR) spectroscopy, since water ice, hydrocarbons, and nitrile compounds display diagnostic absorption bands in this wavelength range. Visible and NIR spectra taken from ground-based facilities have been observed for ∼80 objects so far, covering the full range of spectral types: from neutral to extremely red with respect to the Sun, featureless to volatile-bearing and volatile-dominated (Barkume et al., 2008; Guilbert et al., 2009; Barucci et al., 2011; Brown, 2012). The largest TNOs are bright and thus allow for detailed and reliable spectroscopy: they exhibit complex surface compositions, including water ice, methane, ammonia, and nitrogen. Smaller objects are more difficult to observe even from the largest telescopes in the world. In order to further constrain the inventory of volatiles and organics in the solar system, and understand the physical and chemical evolution of these bodies, high-quality NIR spectra of a larger sample of TNOs need to be observed. JWST/NIRSpec is expected to provide a substantial improvement in this regard, by increasing both the quality of observed spectra and the number of observed objects. In this paper, we review the current knowledge of TNO properties and provide diagnostics for using NIRSpec to constrain TNO surface compositions.
Abstract
We combine photometry of Eris from a 6 month campaign on the Palomar 60 inch telescope in 2015, a 1 month Hubble Space Telescope WFC3 campaign in 2018, and Dark Energy Survey data spanning ...2013–2018 to determine a light curve of definitive period 15.771 ± 0.008 days (1
σ
formal uncertainties), with nearly sinusoidal shape and peak-to-peak flux variation of 3%. This is consistent at part-per-thousand precision with the
P
= 15.785 90 ± 0.00005 day sidereal period of Dysnomia’s orbit around Eris, strengthening the recent detection of synchronous rotation of Eris by Szakáts et al. with independent data. Photometry from Gaia are consistent with the same light curve. We detect a slope of 0.05 ± 0.01 mag per degree of Eris’s brightness with respect to illumination phase averaged across
g
,
V
, and
r
bands, intermediate between Pluto’s and Charon’s values. Variations of 0.3 mag are detected in Dysnomia’s brightness, plausibly consistent with a double-peaked light curve at the synchronous period. The synchronous rotation of Eris is consistent with simple tidal models initiated with a giant-impact origin of the binary, but is difficult to reconcile with gravitational capture of Dysnomia by Eris. The high albedo contrast between Eris and Dysnomia remains unexplained in the giant-impact scenario.
We analyzed spectral cubes of Callisto’s leading and trailing hemispheres, collected with the NIRSpec Integrated Field Unit (G395H) on the James Webb Space Telescope. These spatially resolved data ...show strong 4.25 μ m absorption bands resulting from solid-state ^12 CO _2 , with the strongest spectral features at low latitudes near the center of its trailing hemisphere, consistent with radiolytic production spurred by magnetospheric plasma interacting with native H _2 O mixed with carbonaceous compounds. We detected CO _2 rovibrational emission lines between 4.2 and 4.3 μ m over both hemispheres, confirming the global presence of CO _2 gas in Callisto’s tenuous atmosphere. These results represent the first detection of CO _2 gas over Callisto’s trailing side. The distribution of CO _2 gas is offset from the subsolar region on either hemisphere, suggesting that sputtering, radiolysis, and geologic processes help sustain Callisto’s atmosphere. We detected a 4.38 μ m absorption band that likely results from solid-state ^13 CO _2 . A prominent 4.57 μ m absorption band that might result from CN-bearing organics is present and significantly stronger on Callisto’s leading hemisphere, unlike ^12 CO _2 , suggesting these two spectral features are spatially antiassociated. The distribution of the 4.57 μ m band is more consistent with a native origin and/or accumulation of dust from Jupiter’s irregular satellites. Other, more subtle absorption features could result from CH-bearing organics, CO, carbonyl sulfide, and Na-bearing minerals. These results highlight the need for preparatory laboratory work and improved surface–atmosphere interaction models to better understand carbon chemistry on the icy Galilean moons before the arrival of NASA’s Europa Clipper and ESA’s JUICE spacecraft.
CO _2 ice is present on the trailing hemisphere of Ariel but is mostly absent from its leading hemisphere. The leading/trailing hemispherical asymmetry in the distribution of CO _2 ice is consistent ...with radiolytic production of CO _2 , formed by charged particle bombardment of H _2 O ice and carbonaceous material in Ariel’s regolith. This longitudinal distribution of CO _2 on Ariel was previously characterized using 13 near-infrared reflectance spectra collected at “low” sub-observer latitudes between 30°S and 30°N. Here we investigated the distribution of CO _2 ice on Ariel using 18 new spectra: 2 collected over low sub-observer latitudes, 5 collected at “mid” sub-observer latitudes (31°N–44°N), and 11 collected over “high” sub-observer latitudes (45°N–51°N). Analysis of these data indicates that CO _2 ice is primarily concentrated on Ariel’s trailing hemisphere. However, CO _2 ice band strengths are diminished in the spectra collected over mid and high sub-observer latitudes. This sub-observer latitudinal trend may result from radiolytic production of CO _2 molecules at high latitudes and subsequent migration of this constituent to low-latitude cold traps. We detected a subtle feature near 2.13 μ m in two spectra collected over high sub-observer latitudes, which might result from a “forbidden” transition mode of CO _2 ice that is substantially stronger in well-mixed substrates composed of CO _2 and H _2 O ice, consistent with regolith-mixed CO _2 ice grains formed by radiolysis. Additionally, we detected a 2.35 μ m feature in some low sub-observer latitude spectra, which might result from CO formed as part of a CO _2 radiolytic production cycle.
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