Cary Zeitlin

Understanding the Martian soil water budget is crucial not only for in situ resource utilization in future human missions to Mars, but also for reconstructing the geological and climatic history of the planet, as well as to assess the potential of ancient or even present microbial life. Here, we present a methodology to study near‐surface water using albedo protons, based on measurements from the Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory (MSL). With this approach, water can be investigated beneath dust layers at approximately 1–6 cm, representing a new observational depth range compared to existing methods. In combination with data from the Dynamic Albedo of Neutrons (DAN) experiment, also part of MSL, we show that MSL/RAD has so far been unable to resolve small variations in regolith water of 2%–7%. However, supporting simulations suggest that larger water reservoirs, such as those at higher latitudes or locally near the equator, may be detected by MSL/RAD with measurement times of approximately two to 3 months. We demonstrate that a future Mars detector, specifically redesigned to measure albedo protons, could detect changes in near‐surface water content of about 20% within roughly 6–16 days, and variations exceeding 40% within only a few days, with statistical significance. We therefore propose including albedo proton measurements in future missions to Mars or other extraterrestrial bodies, as they represent a promising complement to existing methods for probing near‐surface water.

The Radiation Assessment Detector (RAD) on the Curiosity rover has been characterizing the Martian surface radiation field since 2012. The dose observed by RAD is influenced by a variety of factors, including an essential one, the terrain. After parking near Murray Buttes in September 2016 where it first detected a ∼5% decrease in dose rate, the rover has passed a series of other interesting terrains where we find decreases in the dose rate reaching 19%. This radiation reduction is due to extra shielding provided by the nearby surface structure, confirming the potential use of surface structures for radiation protection of humans on Mars. Combining a zenith‐angle‐dependent radiation model and the rover panoramic visibility map we calculate the downward radiation dose that RAD should observe under different topographic shielding conditions. This allows us to further evaluate the terrain‐generated albedo dose at different locations. We finally estimate that on a flat surface the albedo radiation is between ∼18% and 24% of the total surface dose. This study contributes to developing a realistic terrain‐based radiation map which is important for future Mars explorers.

Since landing in 2012, the Radiation Assessment Detector (RAD) onboard the Mars science laboratory (MSL) Curiosity rover has encountered different local landscapes, which have induced variations in the local surface environment. The aim of this study is to include realistic and site‐specific local topography for any position in a radiation transport model, and to validate this modeling strategy by comparison with MSL/RAD results. We present a method that integrates complex planetary surface models into neutron transport simulations to assess how surface heterogeneities influence secondary neutron environments—combining flexible terrain representation with radiation transport modeling. By modeling the topography of the main sites traversed by the rover, we show and quantify the dependence of downward neutron intensity on topography, in particular on the blocking zenith angle, across the different energy ranges: thermal, epithermal, fast neutrons. Using a method involving the visible surface from an observation point, we reconstruct the additional albedo neutron environment created by the terrain as seen by MSL/RAD, using the Atmospheric RAdiation Model for Ionizing spectra on martian Surface (ARAMIS). In particular, we show that the terrain‐generated thermal neutron spectrum increases with greater topographic relief, while the flux of high‐energy neutrons (>1 MeV) decreases.

\setlength{\parindent}{0pt} Understanding the Martian soil water budget is crucial not only for in situ resource utilization in future human missions to Mars, but also for reconstructing the geological and climatic history of the planet, as well as to assess the potential of ancient or even present microbial life. Here, we present a methodology to study near-surface water using albedo protons, based on measurements from the Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory (MSL). With this approach, water can be investigated beneath dust layers at approximately 3–7 cm, representing a new observational depth range compared to existing methods. In combination with data from the Dynamic Albedo of Neutrons (DAN) experiment, also part of MSL, we show that MSL/RAD has so far been unable to resolve small variations in regolith water of 2–7\%. However, supporting simulations suggest that larger water reservoirs, such as those at higher latitudes or locally near the equator, may be detected by MSL/RAD with measurement times of approximately two to three months. We demonstrate that a future Mars detector, specifically redesigned to measure albedo protons, could detect changes in near-surface water content of about 20\% within roughly 6–16 days, and variations exceeding 40\% within only a few days, with statistical significance. We therefore propose including albedo proton measurements in future missions to Mars or other extraterrestrial bodies, as they represent a promising complement to existing methods for probing near-surface water.

The topographic influence of the radiation environment on the Martian surface radiation is crucial for future human exploration. Topographic maps help assess radiation flux variations, aiding in hazard evaluation. Creating a global radiation map requires accounting for seasonally varying atmospheric density, heliospheric modulation, and topography. Here, we use a radiation model to derive the flux of secondary downward particles generated by the interaction of primary protons with the Martian atmosphere. Our model examines two key factors: (a) the dependence of atmospheric column depth on the zenith angle, affecting radiation directionality as horizon‐arriving particles traverse more atmosphere than vertical ones and (b) atmospheric conditions at surface heights in Gale Crater, crucial for developing radiation dose maps that incorporate topographic effects. Our model is validated against Radiation Assessment Detector measurements and benchmarked with existing models. We construct response matrices representing the ratio of secondary particles at the Martian surface to primary inputs across zenith angles, assessing atmospheric effects. We combine these matrices with the incident spectrum to compute secondary particle fluxes from all zenith angles for Galactic Cosmic Rays and Solar Energetic Particles. These fluxes will be integrated into a topographic map of Mars in a follow‐up study, providing a detailed representation of surface radiation levels across different terrains. This approach aids mission planners in identifying safe landing sites for astronauts.

Since landing in 2012, the Radiation Assessment Detector (RAD) onboard the Curiosity rover has encountered different local landscapes, which have induced variations in the local surface environment. The aim of this study is to include realistic and site-specific local topography for any position in a radiation transport model, and to validate this modeling strategy by comparison with MSL/RAD results. We present a method that integrates complex planetary surface models into neutron transport simulations to assess how surface heterogeneities influence secondary neutron environments — combining flexible terrain representation with radiation transport modeling. By modeling the topography of the main sites traversed by the rover, we show and quantify the dependence of downward neutron intensity on topography, in particular on the blocking zenith angle, across the different energy ranges: thermal, epithermal, fast neutrons. Using a method involving the visible surface from an observation point, we reconstruct the additional albedo neutron environment created by the terrain as seen by MSL/RAD, using the Atmospheric RAdiation Model for Ionizing spectra on martian Surface (ARAMIS). In particular, we show that the terrain-generated thermal neutron spectrum increases with greater topographic relief, while the flux of high-energy neutrons (> 1 MeV) decreases.

The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) aboard the Lunar Reconnaissance Orbiter spacecraft has been operating in lunar orbit since 2009. CRaTER data provide a long‐term record of the near‐Moon radiation environment that is relevant to human exploration. In considering requirements for operational instruments on crewed lunar missions that are anticipated in the next several years, the question arises whether real‐time measurements by existing assets such as Geostationary Operational Environment Satellite (GOES) are adequate for providing radiation warnings for the safety of astronauts on or near the Moon during Energetic Solar Particle Events (ESPEs). ESPEs are distinguished from more typical Solar Particle Events (SPEs) by their large fluxes of higher‐energy particles. Here we show direct comparisons of contemporaneous ESPE measurements made in the two locations to establish that the radiation environments in lunar space and in geostationary orbit (GEO) are sufficiently similar to allow the use of GOES as a warning system for crew on or near the Moon. The conclusion is based primarily on data from six ESPEs in the October 2021–October 2024 time frame in which the integral flux of protons with energies greater than 100 MeV exceeded 1 at the event's peak as measured by operational GOES satellites, and to a lesser extent on data from two earlier ground‐level events (GLEs) that are of particular interest. We report new methods for analyzing CRaTER data under high‐flux conditions and find good agreement with data reported by GOES‐16 and later satellites.

In addition to the omnipresent Galactic Cosmic Rays, sudden Solar Energetic Particle (SEP) events present considerable health hazards for manned space missions. These events not only contribute to an increased long‐term cancer risk, but can, in extreme cases, cause acute radiation syndromes. Forecasting their imminent occurrence could significantly reduce radiation exposure by warning astronauts to move to shelter. However, all currently available tools are primarily designed for the Earth or Earth‐Moon system, which limits their applicability to future Mars missions. To address this, we developed a nowcasting system for SEP events applicable in deep space and on the Martian surface, which serves as a reliable last‐resort backup when forecasts fail. The methodology of this system is based on dose rates measured by the Radiation Assessment Detector onboard the Mars Science Laboratory, which recorded 5 SEP events during the 7‐month flight to Mars and 17 since its landing on Mars on 6 August 2012. An SEP event is triggered, and an astronaut is warned as soon as dose rates exceed the omnipresent background level by at least 25%. This approach suggests that our system can provide astronauts with at least 30 min to avoid both peak radiation exposure and the majority of the cumulative dose from SEP events. Our nowcasting system is robust, easily implementable in real‐life scenarios, and achieves a near‐zero false alarm rate both in deep space and on the Martian surface.

In addition to the omnipresent Galactic Cosmic Rays (GCRs), sudden solar energetic particle (SEP) events present considerable health hazards for manned space missions. These events not only contribute to an increased long-term cancer risk, but can, in extreme cases, cause acute radiation syndromes. Forecasting their imminent occurrence could significantly reduce radiation exposure by warning astronauts to move to shelter. However, all currently available tools are primarily designed for the Earth or Earth-Moon system, which limits their applicability to future Mars missions. To address this, we developed a nowcasting system for SEP events applicable in deep space and on the Martian surface, which serves as a reliable last-resort backup when forecasts fail. The methodology of this system is based on dose rates measured by the Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory (MSL), which recorded 5 SEP events during the seven-month flight to Mars and 16 since its landing on Mars on August 6, 2012. An SEP event is triggered, and an astronaut is warned as soon as dose rates exceed the omnipresent background level by at least 25%. This approach suggests that our system can provide astronauts with at least 30 minutes to avoid both peak radiation exposure and the majority of the cumulative dose from SEP events. Our nowcasting system is robust, easily implementable in real-life scenarios, and achieves a near-zero false alarm rate both in deep space and on the Martian surface.

The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) aboard the Lunar Reconnaissance Orbiter spacecraft has been operating in lunar orbit since 2009. CRaTER data provide a long-term record of the near-Moon radiation environment that is relevant to human exploration. In considering requirements for operational instruments on crewed lunar missions that are anticipated in the next several years, the question arises whether real-time measurements by existing assets such as Geostationary Operational Environment Satellite (GOES) are adequate for providing radiation warnings for the safety of astronauts on or near the Moon during Energetic Solar Particle Events (ESPEs). ESPEs are distinguished from more typical Solar Particle Events (SPEs) by their large fluxes of higher-energy particles. Here we show direct comparisons of contemporaneous ESPE measurements made in the two locations to establish that the radiation environments in lunar space and in geostationary orbit (GEO) are sufficiently similar to allow the use of GOES as a warning system for crew on or near the Moon. The conclusion is based primarily on data from six ESPEs in the October 2021 to October 2024 time frame in which the integral flux of protons with energies greater than 100 MeV exceeded 1 cm$^{-2}$ sr$^{-1}$ s$^{-1}$ at the event’s peak as measured by operational GOES satellites, and to a lesser extent on data from two earlier ground-level events (GLEs) that are of particular interest. We report new methods for analyzing CRaTER data under high-flux conditions and find good agreement with data reported by GOES-16 and later satellites.