Abstract | The illumination geometry occurring at Mercury’s poles are largely varying during the hermean
year [1]. In particular, Permanent Shadowed Regions (PSRs), occurring on deep craters and rough
terrains, experience multiple scattered light coming from nearby illuminated areas. Despite the
orbital vicinity to the Sun, Mercury’s PSRs can maintain cryogenic temperatures across geological
timescales thus favoring the condensation and accumulation of volatile species [2]. The total
surface area of PSRs between latitudes 80-90° south is estimated at about 25.000 km 2 [3], about
two times larger than the same geographic area on the North Pole [4]. The exploration of surface
ices in polar regions’ PSRs [5] is one of the primary targets of the VIHI imaging spectrometer [6],
one of the three optical channels of the SIMBIO-SYS experiment [7] on ESA’s BepiColombo
mission. The illumination conditions occurring on the PSR located in craters’ floor could allow the
detection of water ice from orbit within the shadowed areas thanks to the light scattered by the
illuminated portion of the crater’s rim [1]. Moreover, the extended dimension of the Sun (between
1.15° and 1.75° at perihelion and aphelion, respectively) causes the presence of blurred shadows
(penumbras) favoring a further faded illumination towards otherwise shadowed areas. In this work,
we extend similar spectral simulations to other volatile species apart from water ice, like SO 2 , H 2 S,
and volatile organics, intending to verify their detectability from orbit and to optimize VIHI
observations. The spectral simulations, performed following the method described in [8], and
including the ice-regolith mixing (areal or intimate) as modeled in [9], allow for exploring different
volatile species abundances and grain size distribution. The resulting ices detection threshold is
evaluated through the computation of VIHI’s instrumental signal-to-noise ratio as given by the
instrumental radiometric model [10].
[1] Filacchione G. et al., MNRAS, 498, 1308-1318, 2020.
[2] Paige D. A. et al., Science, 339, 300, 2013.
[3] Chabot N. L. et al., J. Geophys. Res., 123, 666, 2018.
[4] Deutsch A. N. et al., Icarus, 280, 158, 2016.
[5] Rothery, D. A., et al., Space Sci. Rev., 216, 66, 2020.
[6] Capaccioni F. et al., IEEE Trans. Geosci. Remote Sens., 48, 3932, 2010.
[7] Cremonese G. et al., Space Sci. Rev., 216, 75, 2020.
[8] Raponi A. et al., Sci. Adv., 4, eaao3757, 2018.
[9] Ciarniello. M. et al., Icarus, 214, 541, 2011.
[10] Filacchione G. et al., Rev. Sci. Instrum., 88, 094502, 2017. |
