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As we look for traces of ancient life on Mars, we need to consider the impact of ionizing radiation in the biosignature preservation process. Here, we irradiated two organic rich terrestrial samples (Enspel and Messel shales) that have Martian analog mineralogies, with simulated cosmic rays to a dose of 0.9 MGy, equivalent of 15 million years of radiation exposure on the Martian surface. We compared a range of biosignatures before and after exposure, including total organic carbon, bulk stable carbon isotope ratios, diagnostic lipid biomarkers (hopanes and steranes), and Raman signatures akin to those collected by the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument on Perseverance. While we did not observe a significant difference in total organic carbon, bulk stable carbon isotopes, or Raman G-band signatures, we found that five lipid biomarkers decreased by a factor of two to three in the Enspel shale. This degree of degradation exceeds current predictions by existing models or experimental studies in organic rich samples and challenges our current understanding of complex biosignatures under ionizing irradiation. 

We present the discovery of an Earth-mass planet (M_bsini= 1.26 ± 0.21M_⊕) on a 15.6 d orbit of a relatively nearby (d ~9.6 pc) and low-mass (0.167 ± 0.011M_⊙) M5.0 V star, Wolf 1069. Sitting at a separation of 0.0672 ± 0.0014 au away from the host star puts Wolf 1069 b in the habitable zone (HZ), receiving an incident flux ofS= 0.652 ± 0.029S_⊕. The planetary signal was detected using telluric-corrected radial-velocity (RV) data from the CARMENES spectrograph, amounting to a total of 262 spectroscopic observations covering almost four years. There are additional long-period signals in the RVs, one of which we attribute to the stellar rotation period. This is possible thanks to our photometric analysis including new, well-sampled monitoring campaigns undergone with the OSN and TJO facilities that supplement archival photometry (i.e., from MEarth and SuperWASP), and this yielded an updated rotational period range ofP_rot= 150–170 d, with a likely value at 169.3_−3.6^+3.7. The stellar activity indicators provided by the CARMENES spectra likewise demonstrate evidence for the slow rotation period, though not as accurately due to possible factors such as signal aliasing or spot evolution. Our detectability limits indicate that additional planets more massive than one Earth mass with orbital periods of less than 10 days can be ruled out, suggesting that perhaps Wolf 1069 b had a violent formation history. This planet is also the sixth closest Earth-mass planet situated in the conservative HZ, after Proxima Centauri b, GJ 1061 d, Teegarden’s Star c, and GJ 1002 b and c. Despite not transiting, Wolf 1069 b is nonetheless a very promising target for future three-dimensional climate models to investigate various habitability cases as well as for sub-m s⁻¹RV campaigns to search for potential inner sub-Earth-mass planets in order to test planet formation theories.