{'fraction_non_alphanumeric': 0.03726469458317326, 'fraction_numerical': 0.008835958509412217, 'mean_word_length': 4.945205479452055, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 1, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Ionizing Radiation on the Surface of Europa: Implications for the Search for Evidence of Life

Introduction: Europa’s subsurface ocean is a possible abode for life, but it is inaccessible with current technology. However, ‘Chaos’ regions on the surface might provide direct access to materials originated from shallow pockets of liquid water within the ice shell, or even the subsurface ocean itself [1–6]. These would be ideal locations to search for possible evidence of life, such as organic biomarkers. The best case environment for such evidence would be the orbital “upstream” hemisphere, shielded from much of Jupiter’s radiation belt flux, but where galactic cosmic rays (GCRs) still interact with surface materials. GCRs that strike unimpeded Europa’s surface produce ionizing radiation in the form of high-energy electrons, protons, gamma rays, neutrons and muons. The effects of ionizing radiation in matter always involve the destruction of chemical bonds and the creation of free radicals. Both can destroy organic biomarkers over time [7, 8]. Using ionizing radiation transport codes, we recreated the most-favorable radiation environment on the surface of Europa, and evaluated its possible effects on organic biomarkers within the shallow ice-shell. Methods: We performed a full Monte-Carlo simulation of the nuclear reactions induced by the Galactic cosmic rays hitting Europa’s surface using the Planetcosmic code (http://cosray.unibe.ch/~laurent/ planetocosmics/) [9]. This code is based on the GEANT-4 toolkit for the transport of particles through matter. The computational domain was comprised of 20 m of water ice. To model the GCR primary spectra for Z = 1-26 (protons to iron nuclei) we assumed the CREAME96 model under solar minimum [https:// creme96.nrl.navy.mil/]. Results: Our preliminary results show that the flux of ionizing radiation as a function of depth in Europa’s ice shell is similar in magnitude to that estimated for the surface on Mars for pure ice [10], see Figure 1. As expected, pure ice results in an extensive environment of energetic neutrons, protons, electrons, muons and gamma rays, whose flux is highest within the top few meters. The flux of ionizing radiation can be converted into dosage at the molecular level using a a “biologically-weighted” scheme [10]. The derived radiation dose at 1 meter depth is 0.3 Gy/year. We emphasize that these results likely represent a best-case scenario for Europa, an estimation of the radiation environment resulting from galactic cosmic rays alone. Further work will focus on also taking into account the Jovian