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Protecting astronauts from the effects of space radiation remains one major stepping stone for the exploration of Mars. Long‐term exposure to radiation can lead to severe health effects and affects allowable mission duration. Mission designs for Mars include the use of radiation shelters that provide additional mass to surround the astronauts. This leads to incoming radiation losing energy through ionization processes. This is important during solar energetic particle events when solar protons can reach the surface with high intensities. Additionally, shelters provide a long‐term reduction of the exposure to galactic cosmic rays. As mass is an important time and cost factor in space travel, using natural sheltering already on Mars is a desirable option. One candidate is to use subterranean lava tubes that provide shelter from the radiation from above. Other options include craters, cliff walls, or rock overhangs. Here, we present the first in situ measurements of radiation sheltering by natural environments on the surface of Mars. The data were acquired with the Radiation Assessment Detector (RAD) on board the Curiosity rover in Gale crater on Mars. We show measurements from when Curiosity was parked close to Butte M12 in the Murray Buttes formation, which blocked out 19% of the surrounding sky view. During this time, from Mars Science Laboratory (MSL) sol 1456–1467, we find a decrease of 4% in the expected dose rate, and a decrease of 7.5% in the neutral particle environment. This proof of principle is an important step to validate plans to use natural sheltering on Mars. Plain Language Summary: Protecting astronauts on Mars from the exposure to space radiation remains one of the major challenges for the human exploration of the red planet. A viable option for this is to provide the astronauts with a radiation shelter that surrounds the astronauts with enough mass and material to reduce the effects of radiation. Since bringing additional material from Earth to Mars is extremely time and cost prohibitive, making use of natural terrain and rocks on Mars would theoretically be ideal for this purpose. Here, we present the first‐ever measurements taken on Mars with the Radiation Assessment Detector (RAD) that prove that natural terrain provides such radiation protection. While NASA's Curiosity rover was parked up close to a butte for 12 days, RAD measured a distinct decrease in radiation dose. This was due to the butte blocking out part of the sky and, thus, shielding the rover from the space radiation coming from the direction of the butte. Key Points: We present the first in situ measured proof of principle of radiation sheltering by natural terrain on the surface of MarsWe find that a Martian butte, blocking out 19% of the sky, decreases the radiation dose measured by Mars Science Laboratory (MSL)/Radiation Assessment Detector (RAD) by 4%We find that the Martian surface neutral radiation environment also decreases by 7.5% due to the sheltering provided by the butte [ABSTRACT FROM AUTHOR]

In deep space, personnel and equipment are exposed to the space radiation environment in the form of energetic particles, specifically galactic cosmic rays and sporadic solar energetic particle events. Radiation fields resulting from these particles are modified by shielding, but most radiation measurements in deep space have been made with detectors that were unshielded or very lightly shielded. In contrast, the space radiation environment on the International Space Station (ISS) is more complicated, with time‐dependent modification of the incident flux by the geomagnetic field and complex bulk shielding distributions; measured particle spectra inside the ISS are affected by both types of shielding. The geomagnetic field is also responsible for the existence of the South Atlantic Anomaly, a region of trapped energetic protons and electrons, and hence enhanced radiation dose, through which the ISS travels several times per day on average. Here our primary aim is to compare charged‐particle spectra at high linear energy transfer obtained by the Anomalous Long‐Term Effects in Astronauts instrument on ISS during high‐latitude portions of the orbit to data acquired at the same time by the Cosmic Ray Telescope for the Effects of Radiation and Radiation Assessment Detector instruments, both in deep space. The hypothesis being tested is that these spectra are the same, modulo shielding differences, since the effects of the geomagnetic field are expected to be minimal at high latitudes. Plain Language Summary: Exposure to highly energetic particle radiation in space is a concern for current and future human missions. To date, only the Apollo astronauts have ventured outside the protective effects of the Earth's magnetic field, but astronauts on future missions back to the Moon, or to Mars or other destinations in deep space, will not have this protection. In the high‐latitude parts of the orbit of the International Space Station, the magnetic shielding is weak, and in principle we expect the radiation environment there to be very similar to that in deep space. Here we present the first direct test of this hypothesis, using data obtained by three different particle detectors, one aboard the ISS, one in lunar orbit, and one that was in interplanetary space between Earth and Mars for part of the time period being studied, and on the surface of Mars for the rest of the period of interest. Key Points: We report comparisons of energetic particle spectra taken in low‐Earth orbit at high geomagnetic latitudes to similar data from deep spaceThree instruments were used in the study, one aboard the International Space Station, one in lunar orbit, and one in interplanetary spaceDespite shielding differences, the spectra have many features in common, but fluxes aboard the Space Station are slightly smaller [ABSTRACT FROM AUTHOR]

Although solar activity is declining as the Sun approaches solar minimum, a series of large solar storms occurred in September 2017 that impacted both Earth and Mars. This was the largest event seen on the surface of Mars by the Radiation Assessment Detector on the Mars Science Laboratory Curiosity rover since landing in 2012 and was also observed as Ground Level Enhancement 72 on Earth, making it the first event observed to produce a Ground Level Enhancement on two planets at the same time. We present Radiation Assessment Detector observations of the surface radiation environment since 2012 and discuss the impact of the September 2017 events on this environment and its implications for human exploration and for mitigating the risk of space radiation and space weather events for future manned missions to Mars. Key Points: On 11 September 2017, MSL RAD observed the strongest solar particle event seen on the surface of Mars since landing in 2012Dose rates and neutral particle fluxes increased by factor of 2; proton and 4He fluxes increased by factor of 30 and 10, respectivelyIntegrated dose was only slightly greater than before the event, due to reduced quality factor during the event, and Forbush decrease after the event [ABSTRACT FROM AUTHOR]

Abstract: On 10 September 2017, some of the strongest solar activity occurred in association with active region 12673 (AR2673), including an X‐class solar flare and a fast coronal mass ejection. Although AR2673 was not centrally facing Mars, the activity impacted the local space weather conditions at Mars. We give an overview of observations obtained from the Mars Atmosphere and Volatile EvolutioN, Mars Science Laboratory, and Mars Express missions. Numerical results from the Wang‐Sheeley‐Arge (WSA)‐Enlil‐cone model together with Earth/L1 and STEREO‐A observations are also presented to provide some heliospheric context. We discuss the initial results on the space weather impacts at Mars, which include heating of the upper atmosphere by solar flare emissions, flare‐related enhancements of ion and neutral densities, solar energetic particles impacting the atmosphere and surface, bright emissions of a diffuse (global) aurora, deeply penetrating interplanetary magnetic fields over the Martian dayside, and enhanced atmospheric escape rates. [ABSTRACT FROM AUTHOR]

The nominal radiation environment in low Earth orbit, especially for the International Space Station (ISS), is dominated by two sources. The first is galactic cosmic radiation, which is modulated by the interplanetary and the Earth's magnetic fields, and the second is trapped radiation in the form of the Van Allen belts. The trapped radiation inside the ISS is mostly due to protons of the inner radiation belt. In addition to these sources sporadic solar particle events (SPEs) can produce high doses inside and outside the ISS, depending on the intensity and energy spectrum of the event. Before 2017, the last SPE observed inside the ISS with relevant radiation detectors occurred in May 2012. Even though we are currently approaching the next solar minimum, an SPE was observed in September 2017, which was (a) a ground‐level enhancement, (b) measured with various radiation detector systems onboard the ISS, and (c) observed on the surface of Mars. This paper gives an overview of the 10 September 2017 SPE measured with the DOSIS 3D‐DOSTEL and the ISS‐RAD (Radiation Assessment Detector) instruments, both located at this time in close proximity to each other in the Columbus Laboratory of the ISS. The additional dose received during the SPE was 146.2 μGy in Si as measured by ISS‐RAD and 67.8 μGy in Si as measured by the DOSIS 3D‐DOSTEL instruments. In comparison, the dose measured on the surface of Mars with the Mars Science Laboratory‐RAD instrument accounted to 418 μGy in Si. Plain Language Summary: Severe solar particle events can be the source for deterministic radiation effects on humans, commonly summarized under the term "radiation sickness." We examine the evolution of the solar particle event from 10 September 2017, which was the first event since May 2012 seen inside the International Space Station. Radiation dose values are provided by two instruments (DOSIS 3D‐DOSTEL and ISS‐RAD) positioned in close proximity to each other in the Columbus Laboratory. Key Points: A solar particle event—also seen as GLE 72 on Earth—was measured in September 2017 inside the International Space StationData were provided by two detector systems, DOSIS 3D‐DOSTEL and ISS‐RAD, both in close proximity to each other in the Columbus LaboratoryThe additional absorbed dose due to the 10 September 2017 solar particle event was in the range of 67.8 to 146.2 μGy in Si [ABSTRACT FROM AUTHOR]

Abstract: We report dosimetric quantities measured by the Mars Science Laboratory Radiation Assessment Detector (RAD) on the surface of Mars during the 10–12 September 2017 solar particle event. Despite 23 g/cm2 of CO2 shielding provided by the atmosphere above RAD, dose rates rose above background galactic cosmic ray levels by factors of 2 to 3 over the course of several hours and leveled off at sustained peak rates for about 12 hr before declining over the following 36 hr. As the solar particle event flux was gradually declining, a shock front reached Mars and caused a sudden drop of about 15% in instantaneous dose rates. No solar particles followed the shock arrival, and the magnetic shielding of galactic cosmic rays by the shock reduced their intensity to levels below those seen before the start of the event. This event is the largest seen to date by RAD on Mars. [ABSTRACT FROM AUTHOR]

Abstract: The 10–12 September Solar Energetic Particle event produced the strongest increase of the radiation environment measured by the Radiation Assessment Detector on the surface of Mars since landing in August 2012. We report the details of the measurements of the energetic particle environment from Radiation Assessment Detector in Gale crater during this event. The Solar Energetic Particle event increased the low‐energy proton flux (below 100 MeV) by a factor of 30, and the higher‐energy proton flux by a factor of 4, above preevent levels. The 4He flux (below 100 MeV/nuc) rose by factors up to 10, and neutral particles by a factor of 2 above background. The increase started on 10 September around 19:50 UTC, peak‐level fluxes were reached on the morning of 11 September and prevailed for about 10 hr before decreasing toward background levels. The onset of a Forbush decrease on 13 September decreased the proton flux below preevent intensities. [ABSTRACT FROM AUTHOR]