The Hazards to Human Health in Space: SpaceX's Inspiration4 Mission and Solar Storms on Mars

On Tuesday, the journal Nature released a package of papers studying how only three days in Earth orbit changed the bodies and minds of four people on SpaceX's Inspiration4 mission in 2021.  Kenneth Chang's article for the New York Times is a good brief summary of the findings.  An article by Christopher Mason and his colleagues in Nature is an elaborate survey of the research on space medicine as it has emerged in the "Second Space Age" (Mason et al. 2024).

Inspiration4 was the first space flight with an all-civilian crew--that is, none of them were trained as astronauts.  The four people were private citizens flying on a private spacecraft:  they were in SpaceX's Dragon spacecraft launched into orbit by SpaceX's Falcon 9 rocket.  The spacecraft circled the planet every 90 minutes for three days.  Their highest altitude was 364 miles above the Earth.

The four crew members provided extensive medical data both during and after their flight.  This was combined with data from other people who have flown into space.  This includes the comparative data for Scott Kelly, who lived on the International Space Station for 340 days in 2015 and 2016, and his twin brother, Mark, who is now the senior Senator for Arizona.  

All of this data has been collected in an online archive called the Space Omics and Medical Atlas (SOMA).  Omics is a word used by biologists for the disciplines in biology whose names end in the suffix -omics: such as genomics, proteomics, and metabolomics.  These are nouns with the sense "all constituents considered collectively."  The idea of omics is to collect all the knowledge of the structure and functioning of an organism.  So, SOMA is an ambitious effort to collect all the data on what happens to the human organism in space.

Among the four crew members of Inspiration4, there was evidence of cognitive decline, genetic changes, immune impairment, and molecular changes in their kidneys.  But it also seemed that once they were back on Earth, these alterations in their bodies returned to normal.  Surely, however, people travelling longer and deeper into space will suffer enduring or permanent changes in their minds and bodies that could be dangerous and even deadly.

As I have suggested in previous posts, the fundamental question here is whether evolved human nature is so bound to the biosphere of the Earth that human beings cannot survive and thrive in extraterrestrial space.  Or whether it will be possible to artificially create an Earth-like biosphere in space, so that human beings can live and flourish as a multiplanetary species.

To answer this question, we need to understand the two most important factors in spaceflight that induce cellular and molecular changes in the human body--radiation and microgravity.  We know that radiation can increase the future incidence of cancer.  But there is great uncertainty and disagreement about the rates and causes of radiation-induced cancer both on Earth and in space.

Ionizing radiation consists of subatomic particles or electromagnetic waves that can ionize atoms or molecules by detaching electrons from them.  We are all constantly bombarded by natural background radiation from at least four sources:  terrestrial radiation outside our bodies, radiation in our bodies, solar radiation, and cosmic radiation.  

Terrestrial radiation outside our bodies can come from the geology of the Earth.  For example, the Iranian city of Ramsar, on the Caspian Sea, has some of the highest background radiation in the world because of the radium from radiative rock under the city.  Here the natural background radiation is over 200 times higher than the world average.  And yet, amazingly, there is no clear evidence that the people in Ramsar experience any greater health risk.  This shows how the human body as evolved in adaptation to the range and kinds of radiation on Earth has physiological mechanisms for repairing cells damaged by radiation.

Extraterrestrial radiation comes from the Sun and from other cosmic sources.  On the Earth, we are partially shielded from this radiation by the Earth's thick atmosphere and its magnetosphere (the gravitational field around the Earth).  People living at higher elevations on the Earth or flying in airplanes are exposed to more background radiation.

                                                                      The Northern Lights

The Earth's magnetosphere deflects solar wind particles away from the Earth or directs them to the poles, which creates the Northern Lights (aurora borealis) and the Southern Lights (aurora australis).  Space travelers in low Earth orbit (including those on the Inspiration4 mission and those at the International Space Station) are not protected from radiation by the Earth's atmosphere, but they are protected by the Earth's magnetosphere.

Consequently, we have little experience with the physiological effects of radiation on human beings beyond both the atmosphere and magnetosphere of Earth.  The only experience is from the Apollo missions that went to the Moon and back--24 men.  And the longest was the Apollo 17 mission that lasted a little over twelve days.  So, we have no experience with prolonged space travel in deep space such as the minimum two or three years required for a crewed mission to Mars.

We do know that Mars has a very thin atmosphere (about 1% of the atmospheric pressure at sea level on Earth) and no magnetosphere, and that the gravity on Mars is a little less than 40% of the gravity on Earth.  We do not know much about this Martian environment will affect people on Mars.  But we do know that they will be exposed to many times the level of background radiation faced by people on Earth or in low-Earth orbit.

We also know that the radiation levels on Mars will spike during solar radiation storms--massive energetic particle eruptions from the Sun that spread through the solar system.  In May, we saw one of the strongest solar storms in recent history.  It reached Earth on May 10, causing bright and long-lasting aurorae in North America as far south as the Florida Keys.

It reached Mars on May 20, and NASA's Curiosity rover registered radiation equivalent to 30 chest X-rays.  Although this would not have killed people on the surface of Mars, it might have created some serious health problems (Andrews 2024).

But people like Robert Zubrin who argue "The Case for Mars" say that we should not exaggerate the dangers of radiation on Mars.  After all, NASA scientists can predict solar storms weeks or months in advance, which would give astronauts on Mars plenty of time to protect themselves by hiding behind shielding on the surface or going underground into lava tubes (caves formed by ancient volcanic activity).

Zubrin has estimated that a Mars crew could spend two and a half years in interplanetary space (about a year for a round-trip to Mars and a year and a half on Mars).  During this trip, they would be exposed to about 100 rem of cosmic radiation (rem being the common measurement of radiation in the U.S.), and this would create a 2 percent statistical risk of fatal cancer within 30 years.  By comparison, an average smoker on Earth incurs a 20 percent risk (Zubrin 2019: 134-35; 2021: 126-33).  A Martian living full-time on the surface for 50 years would have an increased risk of 10 percent.  But this could be reduced by living part-time underground (Zubrin 2024: 141-42).  Surely, such a risk from cosmic radiation in space would be bearable for most astronauts.

REFERENCES

Andrews, Robin George. 2024. "Mars Got Cooked by a Recent Solar Storm." New York Times (June 13).

Chang, Kenneth. 2024. "3 Days in Space Were Enough to Change 4 Astronauts' Bodies and Minds." New York Times, June 12.

Mason, Christopher E., et al.  2024.  "A Second Space Age Spanning Omics, Platforms, and Medicine Across Orbits." Nature https://doi.org/10.1038/s41586-024-07586-8.

Zubrin, Robert. 2019. The Case for Space. Amherst, NY: Prometheus Books.

Zubrin, Robert. 2021. The Case for Mars. 25th Anniversary Edition. New York: Free Press.

Zubrin, Robert. 2024.  The New World on Mars: What We Can Create on the Red Planet. New York: Diversion Books.