LASP Science Seminars
Tracing water and organics in the Solar System using ground-based and space telescopes: how important is the UV?
(Instituto de Astrofisica de Canarias & University of La Laguna, Department of Physics)
Primitive asteroids (PAs) are the remaining building blocks of our Solar System (SS) study their composition, location and evolution will help us understanding how different materials travel along the Solar System and how they appeared on Earth. They are characterized by dark surfaces (albedo < 10%) dominated by carbon compounds. Their reflectance spectra are similar to those of carbonaceous chondrites (CCs), the most pristine meteorites in our records, that are abundant in hydrated minerals and organics. PAs present rather featureless spectra in visible and near-infrared wavelengths (from 0.5 to 2.5 µm). The most diagnostic and reliable region to study hydrated mineralogies and organics is the 3-µm region hardly accessible from Earth due to atmospheric absorption. However, another shallow feature in visible wavelengths, around 0.7 µm, is related to the Fe2+ Fe3+ iron transition in hydrated mineralogies. Furthermore, there is a strong absorption in the UV that is proposed to be related also with an electronic iron transition in hydrated minerals. We have observed using different ground-based telescopes ~100 objects with a wavelength coverage enough to study the band at 0.7 microns together with the beginning of the UV absorption. In the archive we found some spectra taken with the Hubble Space Telescope (HST) which allow us to study the beginning of the UV absorption for some asteroids. Furthermore, the Cassini spacecraft have taken images of Iapetus moon of Saturn (which has a deposit of dark carbonaceous material in its surface) covering from the UV to the IR. Finally, in its DR3, Gaia provides more than 60000 slit-less spectra of asteroids with up to 16 bands in the 0.374 – 1.03 µm wavelength range. This allows us to study two main features in the primitive spectra: the beginning of the UV absorption and the 0.7-µm band. As we have different instruments, we are going to study all the spectra by measuring slopes in different wavelength ranges, delimited by the spectral features. We present results on the behavior of the NUV for primitive asteroids using all those facilities. Among our findings there are two main results. (i) the appearance of the 0.7 µm band is strongly correlated with a high UV absorption below 0.5 µm. This feature is present mainly in C-, and G-type asteroids, while, F-type has a smaller drop below 0.4 µm; (ii) another strong correlation between the 3 micron band and the UV absorption is observed by the Cassini data in the Iapetus surface, where we propose the coexistence of 2 different rocky materials or a evolution of 1 of them; (iii) using the slopes in the UV, blue and visible wavelengths as parameters of dimension reduction algorithms we are able to differentiate hydrated and dry mineralogies; (iv) a bimodality on the beginning of the drop in the UV is found from earth, and seems to exists also in the Gaia data.