THE 3–4 μm SPECTRA OF JUPITER TROJAN ASTEROIDS

Brown, Michael E.

doi:10.3847/0004-6256/152/6/159

Cited by 32 publications

(51 citation statements)

References 24 publications

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“…Fastforwarding to more recent work, a study of KLband spectra revealed the first incontrovertible absorption feature centered around 3.1 µm on several Trojans (Brown 2016). This feature has typically been associated with fine surface water frost, but is also consistent with an N-H stretch feature attributable to ammoniated clays.…”

Section: Introductionmentioning

confidence: 63%

“…Irradiation experiments on polystyrene-coated olivine showed the opposite trend, with an initial steep UV and flat visible spectral shape changing to a more linear spectrum with increasing irradiation dosage (Kaňuchova et al 2010). While previous spectral modeling of Trojans has typically limited the mass fraction of complex organics due to the absence of associated major absorption features in the near-infrared (e.g., Jewitt & Luu 2000;Emery & Brown 2003;Dotto et al 2006;Fornasier et al 2007;Emery et al 2011), the KL-band spectra of LR Trojans show minor absorptions at 3.3 and 3.4 µm that are consistent with aromatic and aliphatic hydrocarbons, respectively (Brown 2016).…”

Section: Comparison With Other Published Uv Spectramentioning

confidence: 90%

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Hubble Ultraviolet Spectroscopy of Jupiter Trojans

Wong

Brown

Blacksberg

et al. 2019

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We present the first ultraviolet spectra of Jupiter Trojans. These observations were carried out using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope and cover the wavelength range 200-550 nm at low resolution. The targets include objects from both of the Trojan color subpopulations (less-red and red). We do not observe any discernible absorption features in these spectra. Comparisons of the averaged UV spectra of less-red and red targets show that the subpopulations are spectrally distinct in the UV. Less-red objects display a steep UV slope and a rollover at around 450 nm to a shallower visible slope, whereas red objects show the opposite trend. Laboratory spectra of irradiated ices with and without H 2 S exhibit distinct UV absorption features; consequently, the featureless spectra observed here suggest H 2 S alone is not responsible for the observed color bimodality of Trojans, as has been previously hypothesized. We propose some possible explanations for the observed UV-visible spectra, including complex organics, space weathering of iron-bearing silicates, and masked features due to previous cometary activity.

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Section: Introductionmentioning

confidence: 63%

Section: Comparison With Other Published Uv Spectramentioning

confidence: 90%

Hubble Ultraviolet Spectroscopy of Jupiter Trojans

Wong

Brown

Blacksberg

et al. 2019

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“…It is presumed that other Ceres‐type objects share the surface composition of Ceres (or a similar composition) in the absence of other information to the contrary. The composition of the Themis types is interpreted to include water ice frost and organics (Campins et al, ; Rivkin & Emery, ), though the expected short lifetime for ice on asteroidal surfaces has led to alternate proposed compositions such as goethite (Beck et al, ) or ammoniated minerals (Brown, ).…”

Section: Analysis and Resultsmentioning

confidence: 99%

Infrared Spectroscopy of Large, Low‐Albedo Asteroids: Are Ceres and Themis Archetypes or Outliers?

2019

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Low‐albedo, hydrated objects dominate the list of the largest asteroids. These objects have varied spectral shapes in the 3‐μm region, where diagnostic absorptions due to volatile species are found. Dawn's visit to Ceres has extended the view shaped by ground‐based observing and shown that world to be a complex one, potentially still experiencing geological activity. We present 33 observations from 2.2 to 4.0 μm of eight large (D > 200 km) asteroids from the C spectral complex, with spectra inconsistent with the hydrated minerals we see in meteorites. We characterize their absorption band characteristics via polynomial and Gaussian fits to test their spectral similarity to Ceres, the asteroid 24 Themis (thought to be covered in ice frost), and the asteroid 51 Nemausa (spectrally similar to the CM meteorites). We confirm most of the observations are inconsistent with what is seen in meteorites and require additional absorbers. We find clusters in band centers that correspond to Ceres‐ and Themis‐like spectra, but no hiatus in the distribution suitable for use to simply distinguish between them. We also find a range of band centers in the spectra that approaches what is seen on Comet 67P. Finally, variation is seen between observations for some objects, with the variation on 324 Bamberga consistent with hemispheric‐level difference in composition. Given the ubiquity of objects with 3‐μm spectra unlike what we see in meteorites, and the similarity of those spectra to the published spectra of Ceres and Themis, these objects appear much more to be archetypes than outliers.

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“…Detection of diagnostic spectral absorption features in these groups of Trojans would allow for a detailed mineralogical characterization of their surfaces. The absence of observed features in the 3-µm region by Emery and Brown (2004) Brown (2016) detected spectral curvature between 3.0-3.5 µm in several large lessred Trojans (including Patroclus), which may indicate the presence of ices or organic species and would strengthen the connection between Trojans and a volatile-rich origin. Atmospheric extinction in this wavelength region can limit the definition of the spectral continuum, which is necessary to tie these low signal-to-noise features to a specific hypothesis.…”

Section: Introduction (Trojan Surfaces)mentioning

confidence: 93%

Compositional Constraints for Lucy Mission Trojan Asteroids via Near-infrared Spectroscopy

Sharkey

Reddy

Sanchez

et al. 2019

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We report near-infrared (0.7-2.5 µm) reflectance spectra for each of the six target asteroids of the forthcoming NASA Discovery-class mission, Lucy. Five Jupiter Trojans (the binary (617) Patroclus system, (3548) Eurybates, (21900) Orus, (11351) Leucus, and (15094) Polymele) are well-characterized, with measurable spectral differences. We also report a survey-quality spectrum for main belt asteroid (52246) Donaldjohanson. We measured a continuum of spectral slopes including "red" (Orus, Leucus), "less red" (Eurybates, Patroclus-Menoetius) and intermediate (Polymele), indicating a range of compositional end-members or geological histories. We perform radiative transfer modeling of several possible surface compositions. We find that the mild-sloped spectra and low albedo of Patroclus and Eurybates imply similar compositions. Eurybates (~7 wt.% water ice) and Patroclus (~4 wt.% water ice) are consistent with a hydrated surface. Models for Orus and Leucus are consistent with each other and require a significantly more reddening agent (e.g. iron-rich silicates or tholin-like organics). Polymele has a linear spectrum like Patroclus, but a higher albedo more closely aligned with Orus/Leucus, defying simple grouping. Solar system formation models generally predict that the Jovian Trojans accreted in the outer solar system. Our observations and analysis are generally consistent with this expectation, although not uniquely so.

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THE 3–4 μm SPECTRA OF JUPITER TROJAN ASTEROIDS

Cited by 32 publications

References 24 publications

Hubble Ultraviolet Spectroscopy of Jupiter Trojans

Hubble Ultraviolet Spectroscopy of Jupiter Trojans

Infrared Spectroscopy of Large, Low‐Albedo Asteroids: Are Ceres and Themis Archetypes or Outliers?

Compositional Constraints for Lucy Mission Trojan Asteroids via Near-infrared Spectroscopy

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