For humanity to undertake space travel is to stare extinction in the face.
Space flight may make astronauts infertile, scientists fear and could hinder plans for a long-term mission to Mars.
Animal experiments have shown that both male and female reproductive organs are affected by zero gravity.
It is also likely that space radiation is damaging the ovaries of female astronauts and the sperm production of men.
Previous Russian studies have shown that when male and female rats were sent into space in 1979, they did not mate at all. Another study found that when male rodents were placed in simulated zero gravity conditions, they no longer produce sperm.
Dr. Joseph Tash of the Department of Molecular and Integrative Physiology at the University of Kansas and NASA employee, told a conference in Hawaii that there was concern that astronauts could experience the same effects.
Dr. Tash simulated space flight on rats for six weeks, a duration more like the time astronauts spend on the International Space Station. His results were more dramatic than anything found previously: The rats’ testes shrank and their sperm counts dropped so low the rats were infertile.
Dr. Tash’s experiment with female mice that flew on the space shuttle Discovery in April 2010 showed effects that were equally devastating.
“Fifteen days of spaceflight shuts down the ovaries,” Dr. Tash said.
Dr. Tash and his University of Kansas collaborators, Viju Gupta, Lesya Holets and Katherine Roby, examined the mice shortly after they landed. They found that ovary cells called follicles that produce eggs were dying. And genes involved with the female hormone estrogen had switched off.
“The surprising thing for us was how dramatic it was,” Dr. Tash said.
“We don’t have the human data to really determine whether what we are seeing in the animals is translatable to humans. But we are seeing big impacts in the animals,” he said.
Dr. Tash believes that space flight can disrupt important chemical reactions which must happen in the body to allow for reproduction.
Astronauts report a range of problems when they are at zero gravity in the condition known as ‘space flight syndrome’. It causes bone mass loss and accelerated ageing of cells.
Dr. Task discovered that many of the systems that are shutting down in space flight syndrome are linked to the hormone oestrogen.
Cosmic radiation may also be harming fertility and is expected to increase over the next 20 years because the Sun is entering a quiet phase where there are fewer solar winds to keep radiation out of our galaxy.
Around 80 percent of male astronauts have experienced some kind of reported visual impairment after around ix to eight weeks in space. The majority need glasses when they come back to Earth.
Health experts believe the joint impact of radiation and micro-gravity is responsible.
“The testes are known to be the part of the body that is most sensitive to radiation,” said Dr. Tash.
“The eyes are the next most sensitive, and a lot of long-term astronauts are coming back with eye problems. So it would suggest that the testes must have already been exposed.”
Female astronauts are known to be more susceptible to space radiation and generally spend 30 per cent less time in space.
The Mars One mission is currently scheduled to land its first crew on the planet in 2025, but it has warned volunteer that conception may not be possible in reduced gravity and that a fetus born on Mars may not develop properly.
Astronauts traveling to Mars will be exposed to high levels of radiation, not only because of the length of the mission, between six and eight months, but also because most of the journey is outside of Earth’s protective magnetic field.
NASA has deceptively offered to freeze the sperm cells and ovarian cells of astronauts, knowing that female astronauts will not have viable ovarian cells and male astronauts will be shooting blanks.
However, frozen cells are not a solution because a female astronaut returns to Earth with a permanently disrupted hormonal system and damaged reproductive organs. When a species cannot reproduce its days are numbered.