Ceres is the largest object in the asteroid belt, and a target of the Dawn mission . Recent work suggests
Ceres is a complex object with a rocky core over an icy mantle, perhaps with a primitive crust, and the prospect for profound chemical evolution having occurred over its history.
Despite 30+ years of observations, interpretations of its surface composition still disagree on the presence / absence of water ice, ammonium (NH
4
+ ), and whether any of the meteorites in our collections are good analogs for the composition of Ceres .
HST image of Ceres (J. Parker PI)

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Atmospheric transmission vs. wavelength (bottom), compared to meteorite spectra (top)
The spectrum of Ceres contains few diagnostic absorption features at visible wavelengths, so the 3-
 m region, where OH and H
2
O produce diagnostic absorptions in minerals, is critical for understanding the composition of
Ceres.
Due to its superior atmospheric transmission, Mauna Kea is the only northern hemisphere site where the 3-
 m wavelength region can be regularly observed, and the IRTF is one of the few telescopes in the world with the instrumentation necessary for this spectroscopic observation.

We modeled the 2-4
 m spectrum of Ceres averaged over an entire night using a Hapke theory based mixing code. Models with ~5% carbonates (solid lines), an amount similar to what is seen in
CI meteorites, are a much better fit than models with no carbonates (dashed).
When considered in combination with archival KAO data leads to preference for iron-rich clays over ammonium-rich clays .
Furthermore, water ice appears to be excluded at a meaningful level over a large fraction of Ceres’ surface.
Ceres spectra (black and red) compared to CM meteorite (green) and model spectra (other lines)

Objects with Ceres-type bands
(squares) appear in restricted parts of the asteroid belt, compared to
Pallas-type bands (stars)
Along with Earth and Mars,
Ceres is only the third solar system object with evidence for carbonates , supporting models of
Ceres’ chemical evolution that predict release of CO
2 during aqueous alteration. The preference for ironrich clays (also found in CI meteorites) suggest a relatively oxidized precursor material for Ceres .
Other objects are also observed (with the IRTF) to have Ceres-like band shapes, suggesting the use of 3possible
 m band shapes to map out oxidation state of the early solar system .