The level of radiation on Mars in roentgens. Problems that Mars colonizers will face

ESA/ATG medialab

Instruments aboard the ExoMars mission's Trace Gas Orbiter (TGO) helped scientists determine that astronauts could only make one trip to Mars without significant health risks. The main danger is the high levels of radiation associated with galactic cosmic rays, according to an article published in the journal Icarus .

High levels of radiation are considered one of the main obstacles to manned expeditions to Mars. In particular, data from the RAD instrument on board the Curiosity rover, collected during the flight to the red planet, showed that during the trip a person can receive a radiation dose comparable to the maximum permissible - approximately 0.66 sieverts, 95 percent of which comes from galactic cosmic rays , and only 5 percent - from solar radiation. Similar results were obtained in 2014 during observations in lunar orbit using the CRaTER cosmic ray detector installed on board the LRO probe. As his measurements showed, the risk of cancer among astronauts after a 500-day flight to Mars will increase by 4-5 percent.

Igor Mitrofanov and his colleagues from the Space Research Institute of the Russian Academy of Sciences, the Institute of Biomedical Problems of the Russian Academy of Sciences and the Institute of Space Research and Technology of the Bulgarian Academy of Sciences came to similar conclusions by analyzing data collected by the Lyulin-MO dosimetry module installed on board the Russian-European probe TGO, October 2016. The module is part of the Russian FREND neutron detector, and it, like the RAD sensor aboard Curiosity, was turned on for most of the time the probe spent on its flight to the solar system's fourth planet.

“During the six-month mission to Mars and return to Earth, the spacecraft crew will receive approximately 60 percent of the maximum radiation dose that would be tolerated during an astronaut's or astronaut's entire career if the flight were to take place during a time of reduced solar activity,” the article states.

FREND device with dosimetric module Lyulin-MO

The data collected showed that radiation levels in outer space were about 20 percent higher than during Curiosity's flight. Scientists attribute this discrepancy to the fact that the level of solar activity during this period was minimal, which increased the frequency of “shelling” of the probe and all planets with cosmic rays from the interstellar medium. Something similar was recorded by the LRO probe during the last two solar minima.

On average, an astronaut traveling for about a year to Mars will receive approximately 0.7 sieverts of ionizing radiation (about 73 roentgens). Astronauts aboard the ISS receive about 0.3 sieverts per year, while on Earth the annual dose a person receives is about 2.4 millisieverts. As calculations by scientists show, one trip to Mars along the fastest route will “eat up” a little more than half of the maximum total dose of radiation allowed for astronauts during their entire career.

Interestingly, the level of radiation in the orbit of Mars was even higher, and the level of radiation depended very much on whether the planet was shielding ExoMars from the solar wind.

Measurements on the very surface of the planet have not yet been carried out by European and Russian scientists - Mitrofanov and his colleagues plan to carry them out using the Lyulin-ML dosimeter, which will be installed on the landing platform for the European Pasteur rover, now at NPO Lavochkin.

Sergey Kuznetsov

According to data from the Curiosity rover, radiation levels on Mars are almost the same as in low Earth orbit, where the International Space Station is located. But this does not make a visit to the Red Planet safe, since the flight will take quite a long time.

Compared to Earth, Mars lacks a magnetosphere, which protects the planet from galactic and solar radiation. However, there is a thin atmosphere that provides a little protection. According to one of the Curiosity operators, this discovery was the first-ever measurement of the radiation situation on a planet other than Earth. Astronauts will be able to live in such an environment.

The rover's meteorological station received data on the so-called heat tide. The atmosphere begins to heat up from the Sun, expanding and reducing pressure. And on the other side at this time it is cold, there the atmosphere begins to descend and compress.

Due to the rotation of Mars, the bulge with heated air moves along with the bright side from east to west. Curiosity recorded a similar effect by monitoring changes in atmospheric pressure throughout the day. There were also daily dips in the level of charged particles, coinciding with an increase in pressure. It turns out that the Martian atmosphere still provides protection.

At the moment, scientists cannot estimate the daily radiation dose on the Red Planet. However, it is clear that it will be slightly lower than the level recorded by the spacecraft that carried Curiosity. This is precisely what becomes the main problem: over the three years of the flight, the astronauts will be irradiated seven times more than during the same time on the ISS.

Cumulative radiation exposure increases the risk of various cancers, which is why space agencies set limits on the length of stay in space. It is necessary to obtain the exact value of the Martian dose in order to properly protect the astronauts during the flight to the Red Planet.

On top of all this, solar flares still happen, and Curiosity needs to find out how protected Mars is from them.

Naturally, the best option is an underground base or colony in which only robots come to the surface. But it is still worth considering options that allow the astronaut to reach the surface.

Curiosity has a RAD instrument on board to measure the intensity of radiation exposure. During its flight to Mars, Curiosity measured background radiation, and today scientists working with NASA spoke about these results. Since the rover was flying in a capsule, and the radiation sensor was located inside, these measurements practically correspond to the radiation background that will be present in a manned spacecraft.

The result is not inspiring - the equivalent dose of absorbed radiation exposure is 2 times higher than the dose of the ISS. And four - the one that is considered the maximum permissible for a nuclear power plant.

That is, a six-month flight to Mars is approximately equivalent to 1 year spent in low-Earth orbit or two at a nuclear power plant. Considering that the total duration of the expedition should be about 500 days, the prospect is not optimistic.
For humans, accumulated radiation of 1 Sievert increases the risk of cancer by 5%. NASA allows its astronauts to accumulate no more than 3% risk or 0.6 Sievert over their careers. Taking into account that the daily dose on the ISS is up to 1 mSv, the maximum period for astronauts to stay in orbit is limited to approximately 600 days over their entire career.
On Mars itself, radiation should be approximately two times lower than in space, due to the atmosphere and dust suspension in it, i.e. correspond to the level of the ISS, but exact indicators have not yet been published. RAD indicators during the days of dust storms will be interesting - we will find out how good Martian dust is as a radiation shield.

Now the record for staying in near-Earth orbit belongs to 55-year-old Sergei Krikalev - he has 803 days. But he collected them intermittently - in total he made 6 flights from 1988 to 2005.

The RAD device consists of three silicon solid-state wafers that act as a detector. Additionally, it has a cesium iodide crystal, which is used as a scintillator. The RAD is positioned to face the zenith during landing and capture a 65-degree field.

In fact, it is a radiation telescope that detects ionizing radiation and charged particles in a wide range.

Radiation in space comes primarily from two sources: from the Sun, during flares and coronal ejections, and from cosmic rays, which occur during supernova explosions or other high-energy events in our and other galaxies.


In the illustration: the interaction of the solar “wind” and the Earth’s magnetosphere.

Cosmic rays make up the bulk of radiation during interplanetary travel. They account for a share of radiation of 1.8 mSv per day. Only three percent of the radiation accumulated by Curiosity from the Sun. This is also due to the fact that the flight took place at a relatively calm time. Outbreaks increase the total dose, and it approaches 2 mSv per day.

Peaks occur during solar flares.

Current technical means are more effective against solar radiation, which has low energy. For example, you can equip a protective capsule where astronauts can hide during solar flares. However, even 30 cm aluminum walls will not protect from interstellar cosmic rays. Lead ones would probably help better, but this would significantly increase the mass of the ship, which means the cost of launching and accelerating it.

The most effective means of minimizing radiation exposure should be new types of engines, which will significantly reduce the flight time to Mars and back. NASA is currently working on solar electric propulsion and nuclear thermal propulsion. The first can, in theory, accelerate up to 20 times faster than modern chemical engines, but acceleration will be very long due to low thrust. A device with such an engine is supposed to be sent to tow an asteroid, which NASA wants to capture and transfer to lunar orbit for subsequent visit by astronauts.

The most promising and encouraging developments in electric propulsion are being carried out under the VASIMR project. But to travel to Mars, solar panels will not be enough - you will need a reactor.

A nuclear thermal engine develops a specific impulse approximately three times higher than modern types of rockets. Its essence is simple: the reactor heats the working gas (presumably hydrogen) to high temperatures without the use of an oxidizer, which is required by chemical rockets. In this case, the heating temperature limit is determined only by the material from which the engine itself is made.

But such simplicity also causes difficulties - the thrust is very difficult to control. NASA is trying to solve this problem, but does not consider the development of nuclear powered engines a priority.

The use of a nuclear reactor is also promising in that part of the energy could be used to generate an electromagnetic field, which would additionally protect pilots from cosmic radiation and from the radiation of its own reactor. The same technology would make it profitable to extract water from the Moon or asteroids, that is, it would further stimulate the commercial use of space.
Although now this is nothing more than theoretical reasoning, it is possible that such a scheme will become the key to a new level of exploration of the Solar system.

Curiosity examined the level of radiation on the surface of Mars and showed that it roughly corresponds to the level of radiation in low Earth orbit, where the wire has long been

Curiosity examined the level of radiation on the surface of Mars and showed that it is approximately the same as the level of radiation in low Earth orbit, where people spend long periods of time, such as the International Space Station.

A visit to Mars, however, does not make it any less dangerous, since the flight will take quite a long time, and you still need to spend some time on the Red Planet and return to Earth.

Unlike our planet, Mars does not have a magnetosphere, or it is so weak that its influence on any objects can be neglected. But it is the magnetosphere that primarily protects the Earth from a significant portion of radiation, mainly allowing only neutral particles (photons, neutrinos and some others) to pass through and retaining the lion’s share of charged particles. However, Mars has an atmosphere. And although it is thin and rather sparse, it still provides some protection from radiation.

Don Hassler, one of the Curiosity operators, said that this is the first measurement of the radiation situation on any planet other than Earth in human history. He added that astronauts could live in such an environment. It is very lucky that Mars even has such an atmosphere. Strictly speaking, there is an atmosphere on the Moon, but it is so weak there that it can be ignored and equated to the gas component of outer space. On Mars, it is not permissible to ignore the influence of the atmosphere, Hassler emphasized.

The weather station of the Mars rover also revealed a lot about the heat tide. The fact is that the Sun heats the atmosphere of Mars on the side facing the Sun. As a result, the pressure drops and it expands. On the reverse side, cold prevails and therefore the atmosphere there compresses and becomes thinner and sinks.

As Mars rotates around its axis, the bulge of warmer air moves with the sun's side from east to west. All this was confirmed by Curiosity, measuring changes in the pressure of atmospheric gases during the day. And he also recorded the conjugacy of fluctuations in the level of charged particles that are part of the solar and galactic winds. The decrease in penetrating radiation coincided with an increase in atmospheric pressure. That is, when the atmosphere thickens, charged particles penetrate to a lesser extent to the surface of Mars. So the air of the Martian atmosphere still performs a protective function to a certain extent.

Scientists are currently not yet ready to estimate the so-called daily radiation dose of people staying on Mars in the future. But it is clear that it will be much lower than the radiation level recorded by the same Curiosity during its interplanetary flight. As space experts say, this is where the main problem lies. After all, during a three-year trip to the Red Planet (there and back), astronauts can receive approximately seven times more radiation than those who live on the ISS during the same period.

The cumulative dose of ionizing radiation increases the risk of developing malignant tumors and other consequences. The fact is that those particles that have sufficiently strong energy and literally crash into the human body are capable of turning the atoms of our body into ions and even knocking them out of their “rightful” places. This is the dangerous effect of ionized radiation. Therefore, space agencies set strict limits on time spent in outer space. Therefore, it is imperative to know both the radiation levels in outer space and the radiation levels on Mars.

Curiosity has yet to find out to what extent Mars is vulnerable to solar flares, which also have a serious impact on Earth. Therefore, NASA experts believe that at first underground colonies will be built on Mars, and robots will mainly go to the surface.

The science

It's been three months since the Curiosity rover landed on the Red Planet to determine whether Mars is capable of supporting life.

One of the habitability limiting factors important for future manned missions was the level of radiation from cosmic rays and solar particles that hit the planet's surface.

To find out, the rover's radiation measuring instrument, called RAD, collected data regarding daily radiation cycles reaching Curiosity.

The atmosphere of Mars acts as a shield for radiation on the planet's surface. Scientists know this because as the atmosphere thickens, radiation levels drop by 3 to 5 percent.

The problem was that Mars' atmosphere is 100 times thinner than Earth's, which indicates easier penetration of radiation and greater danger for astronauts.

Life on Mars: radiation levels

So will astronauts be able to survive in the Martian environment?

"Absolutely, astronauts will be able to live in this environment", announced principal investigator Dan Hassler. "At least for a limited period of time."

The level of radiation on the surface of Mars is about half what scientists observe during deep space missions. The main problem is the accumulation of radiation over a long period of time.

But what is known for sure is that the mission to Mars will be long - about 3 years, including about 6 months to get there and another six to return. There is a limit in terms of the total dose of radiation that an astronaut can experience.

On a normal day, an astronaut in deep space is protected from radiation. Radiation sickness does not occur immediately. But the scenario could change if astronauts encounter an event that emits large amounts of radiation, such as a solar storm. Besides, astronauts will be exposed to higher levels of radiation en route to the planet than on its surface.

While scientists continue to take measurements, a conclusion about the level of radiation has yet to be made.

"The question is not whether we will go to Mars. The important thing is when we will go there and how best to protect our astronauts," Hassler explained.

Curiosity rover: photos from Mars

1. High-resolution image of the Curiosity rover, taken using its robotic arm.