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Constraints on an exosphere at Ceres from Hubble Space Telescope observations
Author(s) -
Roth Lorenz,
Ivchenko Nickolay,
Retherford Kurt D.,
Cunningham Nathaniel J.,
Feldman Paul D.,
Saur Joachim,
Spencer John R.,
Strobel Darrell F.
Publication year - 2016
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2015gl067451
Subject(s) - exosphere , physics , lyman limit , astrophysics , geometric albedo , brightness , space telescope imaging spectrograph , astronomy , hubble space telescope , hubble ultra deep field , ultraviolet , albedo (alchemy) , redshift , hubble deep field , photometry (optics) , optics , galaxy , intergalactic medium , art history , ion , art , stars , quantum mechanics , performance art
We report far ultraviolet observations of Ceres obtained with the Cosmic Origin Spectrograph (COS) of the Hubble Space Telescope in the search for atomic emissions from an exosphere. The derived brightnesses at the oxygen lines at 1304 Å and 1356 Å are consistent with zero signals within the 1 σ propagated statistical uncertainties. The OI 1304 Å brightness of 0.12 ± 0.20 Rayleighs can be explained by solar resonant scattering from an atomic oxygen column density of (8.2 ± 13.4) × 10 10 cm −2 . Assuming that O is produced by photodissociation of H 2 O, we derive an upper limit for H 2 O abundance and compare it to previous observations. Our upper limit is well above the expected O brightness for a tenuous sublimated H 2 O exosphere, but it suggests that H 2 O production with a rate higher than 4 × 10 26 molecules s −1 was not present at the time of the COS observation. Additionally, we derive an extremely low geometric albedo of ∼1% in the 1300 Å to 1400 Å range.