Solar System bodies undergo to daily and periodical variations of temperature that mainly depend on their closeness to the Sun. It is known that mineral expansion and contraction due to such variations modify the thermal infrared spectra acquired on solid surfaces. Therefore, it becomes crucial to know the best temperature range at which the acquisition itself should be carried out to get reliable information on the mineralogy of such bodies. Here we provide the thermal expansion of olivine between 20 and 298 K determined by X-ray diffraction. Our data reveal the non-linear behaviour of silicates that undergo to low temperatures, where volume variations appear positively correlated with temperatures. Subtle bond-length variations occurring at low temperatures are then expected to minimally affect vibrational absorption positions. We suggest that thermal infrared spectra of those Solar-System surfaces that are not exceeding 300 K provide reliable information about not only the silicate mineral identification but also on their chemical composition, regardless of the instantaneous temperature.

太阳系天体每天都会经历温度的周期性变化，这主要取决于它们与太阳的距离。众所周知，由于这种变化引起的矿物膨胀和收缩会改变在固体表面获得的热红外光谱。因此，了解进行采集的最佳温度范围以获取有关此类物体的矿物学的可靠信息变得至关重要。在这里，我们提供了由 X 射线衍射确定的橄榄石在 20 到 298 K 之间的热膨胀。我们的数据揭示了硅酸盐在低温下的非线性行为，其中体积变化与温度呈正相关。预计在低温下发生的微妙键长变化对振动吸收位置的影响最小。