The study, published by British researchers, shows that increasing levels of cosmic radiation that increase with weakening solar activity could make such journeys hazardous to the health of crew members, raising questions about the feasibility of these missions.
Not long ago, scientists from MIT published a prediction according to which colonists will fly to Mars as part of the controversial Mars One project, may die within two months If they use the technologies that exist or are being developed today. Now it turns out that the road to Mars will also be fraught with serious radiation danger, for them or for any other manned spacecraft that will be launched by another country or company.
Humans want to fly to Mars, travel all over the solar system and even go out into the universe beyond it. Several countries and private organizations are developing programs for manned missions in the coming decades. This is according to a new study led by researchers from the University of New Hampshire published in the journal Space Weather published by the American Geophysical Union (AGU).
The study shows that increasing levels of cosmic radiation that increase with the weakening of solar activity may make such journeys hazardous to the health of crew members, raising questions about the feasibility of these missions.
A new study has revealed that during periods of low solar activity, a 30-year-old astronaut who spends a year in space - long enough to fly to Mars and back - is subject to a constant bombardment of cosmic rays that increase the risk of cancer from radiation above current exposure levels.
If the sun's activity continues to weaken as many scientists predict, the number of days that humans may spend in deep space before reaching the permissible exposure limit may decrease by about 20%, which will increase the risk of manned space flights.
To assess the sun's activity, scientists count sunspots - black dots on the surface of the sun caused by bursts of magnetic activity. When the Sun is active, the frequency of sunspots and the eruption of energetic material from the surface increases, and the Sun's magnetic field strengthens. The Sun's magnetic field has driven cosmic radiation out of the Solar System, but the current trend of decreasing solar activity means the magnetic field is weakening. The weakened magnetic field allows more cosmic rays to penetrate the solar system and increase the radiation hazard to astronauts. According to the authors of the study, the sun's activity reached its lowest level in the entire space age in 2009 during the last solar minimum, and scientists believe that the next minimum will set an even greater negative record when the sun goes down.
"While these conditions do not close the door on long-duration missions to the moon, an asteroid or even Mars, cosmic rays in particular remain a significant factor whose intensity is getting worse and may limit the duration of the missions." says Nathan Schwadron, an assistant professor in the Institute for Earth, Ocean and Space Studies in the Department of Physics at the University of New Hampshire in Durham, and the paper's lead researcher.
"Cosmic rays are the most energetic particles in the universe," says Richard Mwaldt, a physicist at the California Institute of Technology (Caltech) in Pasadena, who was not involved in the research. Supernova explosions in far corners of the universe send galactic cosmic rays hurtling toward the solar system at nearly the speed of light. Their strong energy allows these particles to penetrate almost any material known to man, including the shielding of spacecraft. When cosmic rays penetrate these shields, secondary particles are created that can cause organ damage and lead to cancer, Schwadron adds.
NASA has set a limit for radiation exposure levels that are considered safe. Using measurements from the Cosmic Ray and Radiation Effects Telescope (CRaTER), located on the LRO (Lunar Reconnaissance Orbiter) orbiting the moon, the authors of the study were able to estimate the amount of time it would take the astronauts to reach NASA's maximum exposure level. CRaTER uses a material known as "tissue equivalent plastic" that mimics human muscle to measure radiation levels over time.
The researchers found that it would take less than 400 days for a 30-year-old astronaut to reach these levels of radiation at the level of solar activity as it was at the last solar minimum. If solar activity continues to decline, allowing cosmic radiation levels to increase, those numbers could drop to less than 320 days for a 30-year-old male astronaut and less than 240 days for a 30-year-old female astronaut within 4-6 years, according to the new study. These numbers vary both according to the age and gender of the astronauts and according to the levels of solar activity," the researchers comment.
Schwadron and his colleagues sought to investigate the effects of declining solar activity on humans in space after solar physicists raised the possibility that the current solar cycle, the weakest 11-year cycle in more than 80 years, may be part of a long-term trend of declining solar activity.
According to Mawaldt during the solar minimum of 2009, the lowest number of sunspots was recorded in the last hundred years and the sun's magnetic activity was the weakest since the beginning of the space age.
Now the sun is at a "mini maximum," meaning a maximum expected to be the lowest since modern scientists began directly observing the sun, Schwadron adds. "In the course of time it is becoming clear that the space environment has not returned to its normal state." He says. "We are witnessing a one-way change in the sun's behavior."
Long periods of below-normal solar activity have already been recorded in the past. The best known is an 80-year period known as the Maunder Minimum, which began in the mid-17th century and was characterized by an almost complete absence of sunspots.
Schwadron commented that the solar activity forecasts he used in the study are tentative, and that there is no good ability to estimate how long future space flights will last, but the study nevertheless illustrates how the changes in the solar environment may affect a human journey in space.
"The research helps us prepare and plan human activity in space in the future." Schwadron concludes.