Water abundance at the surface of C-complex main-belt asteroids

Abstract

Recently published space-based observations of main-belt asteroids with the AKARI telescope provide a full description of the 3 μm band, related to the presence of OH bearing minerals. Here, we use laboratory spectra of carbonaceous chondrites obtained under controlled atmosphere (CI,CM,CO,CV,CR Tagish Lake) to derive spectral metrics related to the water content in the samples. After testing several spectral metrics, we use a combination of band depth at 2.75 μm and 2.80 μm that shows a correlation with [H2O] in the sample determined by TGA, though with a high uncertainty (4 wt% H2O). This relation is used to determine water content at the surface of large C-complex main-belt asteroids and discuss the origin of the variability found. On average C-complex Main-Belt Asteroids (MBA) have water contents of 4.5 wt% (volume average, (1) Ceres excluded), significantly lower than average CM chondrites. The estimated water content for the most hydrated asteroids are lower than those of the most hydrated meteorites, a difference that could be attributed to space-weathering. An anti-correlation is also present between water content and overall spectral slope, which is opposite to expectation from laboratory simulations of space weathering on dark carbonaceous chondrites. This suggests that part of the variability in the surface hydration among the different C-complex asteroids is not due to space-weathering, but to the composition of surface material. When applied to Ceres, the hygrometer presented in this work enables us to estimate that at least 1.22 wt% of the hydrogen is present in the form of organics. This richness in organics strengthens the connection between Ceres and cometary materials.

References in corpus (12)

• The origins and concentrations of water, carbon, nitrogen and noble gases on Earth
• Solar System evolution from compositional mapping of the asteroid belt
• SHADOWS: a spectro-gonio radiometer for bidirectional reflectance studies of dark meteorites and terrestrial analogs: design, calibrations, and performances on challenging surfaces
• 3-micron Reflectance Spectroscopy of Carbonaceous Chondrites under Asteroid-like Conditions
• The meteorite flux of the last 2 Myr recorded in the Atacama desert
• Infrared Spectroscopy of Large, Low-Albedo Asteroids: Are Ceres and Themis Archetypes or Outliers?
• The homogeneous internal structure of CM-like asteroid (41) Daphne
• Some things special about NEAs: Geometric and environmental effects on the optical signatures of hydration
• Style and intensity of hydration among C-complex asteroids: a comparison to dessicated carbonaceous chondrites
• Spectral reflectance analysis of type 3 carbonaceous chondrites and search for their asteroidal parent bodies
• A model of the 3-μm hydration band with Exponentially Modified Gaussian (EMG) profiles: application to hydrated chondrites and asteroids
• Spectral investigation of Ceres analogue mixtures: in-depth analysis of crater central peak material (ccp) on Ceres

Cited by in corpus (7)

• Thermal alteration of CM carbonaceous chondrites: mineralogical changes and metamorphic temperatures
• Reflection, emission, and polarization properties of surfaces made of hyperfine grains, and implications for the nature of primitive small bodies
• Metal pollution of the solar white dwarf by solar system small bodies
• A Possible Explanation for the Blue Spectral Slope Observed on B-type Asteroids
• Origins of colors variability among C-cluster main-belt asteroids
• Probing the surface environment of large T-type asteroids
• Multi-wavelength JWST observations of (3200) Phaethon show a dehydrated object with an aqueously altered origin