  Space weathering is an important surface process occurring on the Moon and
other airless bodies, especially those that have no magnetic field. The optical
effects of the Moon's space weathering have been largely investigated in the
laboratory for lunar samples and lunar analogues. However, duplication of the
pristine regolith on Earth is not possible. Here we report the space weathering
from the unique perspective of the Chang'E-3's (CE-3) "Yutu" rover, building on
our previous work (Wang et al. 2017; Wu and Hapke 2018). Measurement of the
visually undisturbed uppermost regolith as well as locations that have been
affected by rocket exhaust from the spacecraft by the Visible-Near Infrared
Spectrometer (VNIS) revealed that the returned samples bring a biased
information about the pristine lunar regolith. The uppermost surficial regolith
is much more weathered than the regolith immediately below, and the finest
fraction is rich in space weathered products. These materials are very dark and
attenuated throughout the visible and near-infrared (VNIR) wavelengths, hence
reduce the reflectance and mask the absorption features. The effects on the
spectral slope caused by space weathering are wavelength-dependent: the visible
and near-infrared continuum slope (VNCS) increases while the visible slope (VS)
decreases. In the visible wavelength, the optical effects of space weathering
and TiO2 are identical: both reduce albedo and blue the spectra. This suggests
that developing new TiO2 abundance algorithm is needed. Optical maturity
indices are composition related and hence only locally meaningful. Since
optical remote sensing can only sense the uppermost few microns of regolith and
since this surface tends to be very weathered, the interpretation of surface
composition using optical remote sensing data needs to be carefully evaluated.
Sampling the uppermost surface is suggested.
