On July 20, American billionaire Jeff Bezos flew a Blue Origin rocket past the Kármán Line, which, at an altitude of 62 miles, is the widely accepted limit of space. The spacecraft peaked 66.5 miles above Earth and its crew experienced a few minutes of weightlessness. Billionaire Richard Branson had reached the 50-mile space limit designated by NASA just nine days earlier. The other billionaire interested in space travel, Elon Musk, runs SpaceX, a company that has taken astronauts to the International Space Station (ISS). Although Musk has yet to be in space, he has made no secret of his desire to take humanity to Mars and return.
Some futurists believe that a permanent colony on Mars will be possible. I don’t expect to see one in my life. The challenges of the journey to Mars and survival on the planet are exceptional. Mars has thin air, freezing weather, and traces of oxygen. And after 10 years on Mars at lower gravity, an astronaut’s legs and bones would be so fragile that re-entry into Earth’s atmosphere would render them useless.
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But one of the biggest risks in space comes from radiation. Ionizing radiation damages cells and the DNA they contain. In deep space, ionizing radiation is of two main types: galactic cosmic rays that originate outside the solar system from exploding stars and solar energetic particles from the Sun.
Radiation poses an existential threat to humans and all other forms of life. Not surprisingly, NASA considers radiation to be one of the major unresolved issues in sustained human spaceflight. Returning astronauts could face an increased risk of various cancers, eye conditions and heart events.
The risks are not unique to humans either. All organisms that accompany humans in space and to Mars should be able to resist ionizing radiation. As Christopher Mason writes in his eminently readable new book, The Next 500 Years: Engineering Life to Reach New Worlds, “Sending an evolved organism on Earth to another planet would result in almost certain death. “
Earth is an incomparable planet. The Earth’s magnetic field is created by currents of electricity that flow through the molten core. Earth’s internal magnetism creates a region around the planet known as the magnetosphere, which protects us from the harmful effects of most radiation from space.
Several planets in our solar system have magnetospheres. Earth is the strongest of all the rocky planets have. Our magnetosphere is a large comet-shaped bubble, which has played an essential role in the habitability of our planet. Life would not exist on the planet without it.
The Earth’s magnetosphere stretches for approximately 40,000 miles. The ISS is positioned at a higher altitude than Bezos or Branson’s flight, and normally maintains a planned altitude of 248 miles. But since it is in low earth orbit, it is still in the earth’s magnetosphere.
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The ISS circles the Earth every 90 minutes at 17,500 miles. Even at this altitude, there are enough molecules in the atmosphere to change its speed and cause it to plunge towards Earth. To maintain a constant orbit, the thruster is pulled to reposition the station.
Astronauts aboard the ISS also experience the effects of radiation during extended visits. When astronaut Scott Kelly, who spent nearly a year on board, closed his eyes, he could see high-energy ion trails flashing like shooting stars. But the radiation he received was far less than that which might be encountered on a future mission to Mars.
The Moon is farther from Earth than the ISS. When Neil Armstrong went to the moon, he wore aluminum plates on his ankles. High energy particle trails can be seen on these plates. But it was a relatively short assignment.
Any attempt to colonize Mars would have to take into account not only radiation exposure on the journey to the Red Planet, but also the planet itself. The current scientific consensus is that Mars has a molten core, but the protection on the planet is much lower than on Earth.
NASA estimates that radiation exposure from a mission to Mars could exceed the life limit of astronauts. Actual limits vary by age and gender. But a 30-month round trip to Mars could result in 1,000 millisieverts, which roughly matches the radiation exposure from 10,000 chest x-rays.
Protecting ships and shielding astronaut exposure is a proposed solution to the massive amounts of radiation while traveling on Mars. It seems to work well against solar energetic particles. But currently, no spacecraft can protect against galactic cosmic rays. Clearly, solutions to the challenge are needed if we are to envision prolonged manned space flight.
In the more distant future, we may see the development of drugs that protect against radiation-induced damage. Another solution could be to genetically improve humans to make them more resistant to DNA damage. Although it seems overkill now, scientists are currently studying animals like tardigrades that have high levels of radiation resistance to learn how they achieve it.
But even as we look at the planets and beyond, it is clear that Earth is our home and that there is no place that looks like it. We take our comfort for granted, but it won’t be found on Mars or anywhere else.
Anirban Mahapatra, a trained microbiologist, is the author of COVID-19: Separating Fact from Fiction
Opinions expressed are personal
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