The surface of (4) Vesta in visible light as seen by Dawn/VIR. (arXiv:2109.09727v1 [astro-ph.EP])

The surface of (4) Vesta in visible light as seen by Dawn/VIR. (arXiv:2109.09727v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Rousseau_B/0/1/0/all/0/1">B. Rousseau</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sanctis_M/0/1/0/all/0/1">M. C. De Sanctis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Raponi_A/0/1/0/all/0/1">A. Raponi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ciarniello_M/0/1/0/all/0/1">M. Ciarniello</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ammannito_E/0/1/0/all/0/1">E. Ammannito</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Frigeri_A/0/1/0/all/0/1">A. Frigeri</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Carrozzo_F/0/1/0/all/0/1">F. G. Carrozzo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tosi_F/0/1/0/all/0/1">F. Tosi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Scarica_P/0/1/0/all/0/1">P. Scarica</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fonte_S/0/1/0/all/0/1">S. Fonte</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Raymond_C/0/1/0/all/0/1">C. A. Raymond</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Russel_C/0/1/0/all/0/1">C. T. Russel</a>

We analyzed the surface of Vesta at visible wavelengths, using the data of
the Visible and InfraRed mapping spectrometer (VIR) on board the Dawn
spacecraft. We mapped the variations of various spectral parameters on the
entire surface of the asteroid, and also derived a map of the lithology. We
took advantage of the recent corrected VIR visible data to map the radiance
factor at 550 nm, three color composites, two spectral slopes, and a band area
parameter relative to the 930 nm crystal field signature in pyroxene. Using the
howardite-eucrite-diogenite (HED) meteorites data as a reference, we derived
the lithology of Vesta using the variations of the 930 nm and 506 nm
(spin-forbidden) band centers observed in the VIR dataset. Our spectral
parameters highlight a significant spectral diversity at the surface of Vesta.
This diversity is mainly evidenced by impact craters and illustrates the
heterogeneous subsurface and upper crust of Vesta. Impact craters also
participate directly in this spectral diversity by bringing dark exogenous
material to an almost entire hemisphere. Our derived lithology agrees with
previous results obtained using a combination of infrared and visible data. We
therefore demonstrate that it is possible to obtain crucial mineralogical
information from visible wavelengths alone. In addition to the 506 nm band, we
identified the 550 nm spin-forbidden one. As reported by a laboratory study for
synthetic pyroxenes, we also do not observe any shift of the band center of
this feature across the surface of Vesta, and thus across different
mineralogies, preventing use of the 550 nm spin-forbidden band for the
lithology derivation. Finally, the largest previously identified olivine
rich-spot shows a peculiar behavior in two color composites but not in the
other spectral parameters.

We analyzed the surface of Vesta at visible wavelengths, using the data of
the Visible and InfraRed mapping spectrometer (VIR) on board the Dawn
spacecraft. We mapped the variations of various spectral parameters on the
entire surface of the asteroid, and also derived a map of the lithology. We
took advantage of the recent corrected VIR visible data to map the radiance
factor at 550 nm, three color composites, two spectral slopes, and a band area
parameter relative to the 930 nm crystal field signature in pyroxene. Using the
howardite-eucrite-diogenite (HED) meteorites data as a reference, we derived
the lithology of Vesta using the variations of the 930 nm and 506 nm
(spin-forbidden) band centers observed in the VIR dataset. Our spectral
parameters highlight a significant spectral diversity at the surface of Vesta.
This diversity is mainly evidenced by impact craters and illustrates the
heterogeneous subsurface and upper crust of Vesta. Impact craters also
participate directly in this spectral diversity by bringing dark exogenous
material to an almost entire hemisphere. Our derived lithology agrees with
previous results obtained using a combination of infrared and visible data. We
therefore demonstrate that it is possible to obtain crucial mineralogical
information from visible wavelengths alone. In addition to the 506 nm band, we
identified the 550 nm spin-forbidden one. As reported by a laboratory study for
synthetic pyroxenes, we also do not observe any shift of the band center of
this feature across the surface of Vesta, and thus across different
mineralogies, preventing use of the 550 nm spin-forbidden band for the
lithology derivation. Finally, the largest previously identified olivine
rich-spot shows a peculiar behavior in two color composites but not in the
other spectral parameters.

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