Which Parts of Mars are the Safest From Cosmic Radiation?

NASA and China plan to send people to Mars in the next decade. In 2033, 2035, 2037, and every 26 months after that, both agencies will send spaceships in order to coincide with Mars being in opposition. The long-term goal of these programs is to establish a base on Mars that will serve as a hub that accommodates future missions, though the Chinese have stated that they intend for their base to be a permanent one.

The prospect of sending astronauts on a six-to-nine-month journey to Mars presents several challenges, to say nothing of the dangers they will face while conducting scientific operations on the surface. In a recent study, an international team of scientists conducted a survey of the Martian environment to find out where the lowest radiation is. Future missions to Mars could be influenced by their findings.

The team was led by a professor from the School of Earth and Space Sciences at the University of Science and Technology of China. He was joined by colleagues from the Institute of Experimental and Applied Physics, the Russian Academy of Science, and the Sko. The paper about their findings was published in the Journal of Geophysical Research.

Radiation is always a concern when it comes to missions to Mars and other locations. Mars has a tenuous atmosphere that is less than 1% of the air pressure, and there is no protective magnetosphere to shield the surface from solar and cosmic radiation. Scientists theorize that harmful particles, such as galactic cosmic rays, could travel directly to the atmosphere and even reach the surface of Mars.

The level of radiation exposure depends on how thick the atmosphere is. TheValles Marineris canyon system and the largest crater on Mars have an atmospheric pressure of over 1.2 and 1.24 kPa, respectively. This is ten times the average atmospheric pressure at high elevation locations like Olympus Mons, and about twice the average of 0.636 kPa.

The co-author on the paper was a professor with the IEAP at Christian-Albrechts-University and a member of the Chinese Academy of Sciences. She told Universe Today via email.

“Different elevation means different atmospheric thickness. High-altitude places generally have a thinner atmosphere on top. High energetic particle radiation needs to traverse through the atmosphere to reach the surface of Mars. If the atmospheric thickness changes, the surface radiation may also change. Thus elevation could influence the surface radiation of Mars.”

The influence of atmospheric depths on Martian radiation levels was considered by the team. The absorbed dose, the dose equivalent, and the body effective dose rates were included. The radiation environment was modeled using a state-of-the-art simulation based on the GEometry And Tracking (GEANT4) software.

The Atmospheric Radiation Interaction Simulator uses Monte Carlo probabilities to model particle interactions with the atmosphere and terrain. Dr. Guo illustrated:

“We use a Monte Carlo approach called ‘GEANT4’ to model the transport and interaction of energetic particles with the Martian atmosphere and regolith. The Mars environment is set up considering the Mars atmospheric composition & structure and regolith properties.

“The input particle spectra on top of the Mars’s atmosphere are obtained also from data-calibrated models which describe the omnipresent particle radiation environment in the interplanetary space that includes charged particles of different species which are mainly protons(~87%), helium ions(12%) and also small traces of heavier ions such as carbon, oxygen and irons.”

They found that higher surface pressures can reduce the amount of heavy-ion radiation, but more shielding is needed. The presence of this shielding can lead to the creation of secondary particles that can flood a habitat with varying levels of neutron radiation. The astronauts will absorb a significant amount of radiation.

The effective dose peak is 30 cm below the surface. Fortunately, these findings offer solutions for shielding. Said Dr. Guo.

The required regolith depth is between 1 m and 100 mSv for a given threshold of the annual biologically-weighted radiation effective dose. At a deep crater where the surface pressure is higher, the needed extra regolith shielding is slightly smaller. Extra regolith shielding is needed on top of Mount Olympus.

The best places for future habitats on Mars would be located in low-lying areas and at depths of 1 m and 1.6 m beneath the surface. Most of the northern hemisphere is made up of the Northern Lowlands. It would be very suitable for these locations. Water ice is abundant beneath the surface of these regions.

If everything goes according to plan, astronauts will be on the surface of Mars in just over a decade. There will be transits lasting six to nine months and surface operations lasting up to 18 months. For up to three years, astronauts will have to contend with elevated radiation. It is necessary to develop detailed mitigation strategies in advance.

NASA and other space agencies have invested considerable time, energy, and resources to develop habitat designs that leverage 3-D printing, In-Situ Resource Utilization, and even electromagnetic shielding to ensure astronauts' health and safety. There are still unanswered questions about how effective these strategies will be in practice, especially when considering the amount of time crews will be spending on the Martian surface.

When designing future Martian habitats using natural surface material as shielding protection, our study may serve for mitigated radiation risks.

Further reading is about JRG Planets.