Traces of life may have been preserved in ancient martian rocks in the form of molecular fossils. Yet the surface of Mars is continuously exposed to intense UV radiation detrimental to the preservation of organics. Because the payload of the next rovers going to Mars to seek traces of life will comprise Raman spectroscopy tools, laboratory simulations that document the effect of UV radiation on the Raman signal of organics appear critically needed. The experiments conducted here evidence that UV radiation is directly responsible for the increase of disorder and for the creation of electronic defects and radicals within the molecular structure of S-rich organics such as cystine, enhancing the contribution of light diffusion processes to the Raman signal. The present results suggest that long exposure to UV radiation would ultimately be responsible for the total degradation of the Raman signal of cystine. Yet because the degradation induced by UV is not instantaneous, it should be possible to detect freshly excavated S-rich organics with the Raman instruments on board the rovers. Alternatively, given the very short lifetime of organic fluorescence (nanoseconds) compared to most mineral luminescence (micro- to milliseconds), exploiting fluorescence signals might allow the detection of S-rich organics on Mars. In any case, as illustrated here, we should not expect to detect pristine S-rich organic compounds on Mars, but rather by-products of their degradation.

中文翻译：

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紫外线辐射对胱氨酸拉曼信号的影响：对检测火星上富含 S 的有机物的意义

生命的痕迹可能以分子化石的形式保存在古老的火星岩石中。然而，火星表面持续暴露在强烈的紫外线辐射下，不利于有机物的保存。由于下一个前往火星寻找生命痕迹的漫游车的有效载荷将包括拉曼光谱工具，因此迫切需要记录紫外线辐射对有机物拉曼信号影响的实验室模拟。这里进行的实验证明，紫外线辐射直接导致无序度的增加以及在富含 S 的有机物（如胱氨酸）的分子结构中产生电子缺陷和自由基，从而增强了光扩散过程对拉曼信号的贡献。目前的结果表明，长时间暴露于紫外线辐射将最终导致胱氨酸拉曼信号的完全降解。然而，由于紫外线引起的降解不是瞬间发生的，因此应该可以使用漫游车上的拉曼仪器检测新挖掘的富含硫的有机物。或者，考虑到有机荧光的寿命（纳秒）与大多数矿物发光（微秒到毫秒）相比非常短，利用荧光信号可能允许在火星上检测富含 S 的有机物。无论如何，如这里所示，我们不应期望在火星上检测到原始的富含 S 的有机化合物，而是它们降解的副产品。应该可以使用漫游车上的拉曼仪器检测新挖掘的富含硫的有机物。或者，考虑到有机荧光的寿命（纳秒）与大多数矿物发光（微秒到毫秒）相比非常短，利用荧光信号可能允许在火星上检测富含 S 的有机物。无论如何，如这里所示，我们不应期望在火星上检测到原始的富含 S 的有机化合物，而是它们降解的副产品。应该可以使用漫游车上的拉曼仪器检测新挖掘的富含硫的有机物。或者，考虑到有机荧光的寿命（纳秒）与大多数矿物发光（微到毫秒）相比非常短，利用荧光信号可能允许在火星上检测富含 S 的有机物。无论如何，如这里所示，我们不应期望在火星上检测到原始的富含 S 的有机化合物，而是它们降解的副产品。