(ORDO NEWS) — In the next decade, NASA and China plan to send the first crews to Mars. Both agencies will send spacecraft in 2033, 2035, 2037 and every 26 months thereafter to coincide with Mars opposition (i.e. when Earth and Mars are in their closest orbits).
The long-term goal of these programs is to establish a base on Mars that will serve as a hub for future missions, although the Chinese have said they intend to make their base permanent.
The prospect of sending astronauts on a six-to-nine-month trip to Mars comes with a number of challenges, not to mention the dangers they face when conducting scientific operations on the surface.
In a recent study, an international team of scientists examined the Martian environment – from the summits of Mount Olympus to its subterranean depths – in order to identify places with the lowest levels of radiation. The findings could help future missions to Mars and the creation of a Martian habitat.
The team was led by Jian Zhang, Associate Professor of the School of Earth and Space Sciences (ESS), China University of Science and Technology.
He was joined by colleagues from ESS and the CAS Center for Comparative Planetology in China, the Institute for Experimental and Applied Physics (IEAP) in Kiel, Germany, the Institute for Biomedical Problems of the Russian Academy of Sciences, and the D.V. Skobeltsyn (INP) in Moscow. An article describing their results recently appeared in Geophysical Research: The Planets.
When it comes to missions to Mars and other places beyond low Earth orbit (LEO), radiation is always a burning issue. Compared to Earth, Mars has a fragile atmosphere (less than 1% atmospheric pressure) and no protective magnetosphere to shield the surface from solar and cosmic radiation.
As a result, scientists suggest that harmful particles, especially galactic cosmic rays (GCRs), can propagate and interact directly with the atmosphere and even reach the interior of Mars.
However, the level of radiative forcing depends on the thickness of the atmosphere, which varies with altitude. In low-lying areas such as the famous canyon system of Mars (Valles Marineris) and its largest crater (Hellas Planitia), atmospheric pressure is estimated at more than 1.2 and 1.24 kPa, respectively.
This is about twice the average value of 0.636 kPa and 10 times the atmospheric pressure at high altitude places like Mount Olympus (Olympus Mons is the largest mountain in the solar system).
Dr. Jingnan Guo, IEAP Professor at Christian Albrechts University and Member of the Chinese Academy of Sciences (CAS), was Professor Jian Zhang’s supervisor and co-author of the paper.
“Different altitudes mean different thicknesses of the atmosphere. High altitude places tend to have a thinner atmosphere on top.
Radiation from high-energy particles must pass through the atmosphere to reach the surface of Mars. If the thickness of the atmosphere changes, then the radiation at the surface may also change. Thus Thus, altitude can affect the surface radiation of Mars.”
To this end, the team looked at the effect of atmospheric depth on Martian radiation levels. It included absorbed dose, measured in radians; dose equivalent, measured in rems and sieverts (Sv); and effective dose rate on the body induced by GCR.
The process consisted in modeling the radiation environment using a modern simulator based on the GEometry And Tracking (GEANT4) software developed by CERN.
Known as the Atmospheric Radiation Interaction Simulator (AtRIS), this software uses probabilistic Monte Carlo algorithms to simulate particle interactions with the Martian atmosphere and terrain.
We use a Monte Carlo approach called “GEANT4” to model the transport and interaction of energetic particles with the Martian atmosphere and regolith. The Martian environment is specified taking into account the composition and structure of the Martian atmosphere and the properties of the regolith.
“The input spectra of particles at the top of the Martian atmosphere are derived from models that describe the ubiquitous radiation environment of particles in interplanetary space, including charged particles of various kinds, which are mainly composed of protons (~87%), helium ions (12%), as well as small traces of heavier ions such as carbon, oxygen and iron.”
They found that higher surface pressure can effectively reduce the amount of heavy ion radiation (GCR), but additional shielding is still needed. Unfortunately, the presence of such protection can lead to “cosmic ray showers”, when the impact of the GCR on the protective shell creates secondary particles that can fill the interior of the habitat with various levels of neutron radiation (the so-called neutron flux). This can make a significant contribution to the radiation dose that the astronauts will receive.
They determined that both the neutron flux and the effective dose peak at about 30 cm below the surface. Fortunately, these results provide a solution to the problem of using Martian regolith for shielding. Doctor Guo said:
“For a given threshold for an annual biologically weighted dose of radiation, such as 100 mSv (a value often considered the threshold below which the risk of radiation-induced cancer is negligible), the required regolith depth varies between 1 and 1.6 m. Within this range , in a deep crater, the required additional protection of regolith is needed a little less. While at the top of Mount Olympus, the additional protection from regolith is needed more.”
Based on the findings, the best locations for future habitats on Mars would be in low-lying areas and 1 to 1.6 meters below the surface.
Therefore, the Northern Lowlands, which make up most of the northern hemisphere (aka Vastitas Borealis), and Valles Marineris would be very suitable places. In addition to higher atmospheric pressure, these regions also have large amounts of water ice just below the surface.
If all goes according to plan, astronauts will set foot on the Martian surface in just over a decade. These will be flights lasting six to nine months (unless better propulsion technology is developed) and surface work up to 18 months.
In short, astronauts will have to deal with the threat of increased radiation for three years. Therefore, it is necessary to develop detailed strategies in advance to reduce exposure to radiation.
NASA and other space agencies have spent a lot of time, energy and resources developing habitat designs that use 3D printing, in situ resource utilization (ISRU), and even electromagnetic shielding to ensure the health and safety of astronauts.
However, there are still unresolved questions about how effective these strategies will be in practice, especially considering how much time the crews will spend on the Martian surface.
“Our study may serve to reduce radiation risks when designing future Martian habitats using natural surface material as a protective shield,” Dr Guo said. “A study like this will go a long way as mission planners begin to consider designs for future Martian habitats that use natural material on the surface to shield against radiation.”
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