Thomas Pesquet returned to Earth, with three other astronauts, on the night of Monday to Tuesday, aboard SpaceX's Dragon capsule.
The 43-year-old astronaut led a six-month stay in orbit on the International Space Station, a first for a Frenchman.
But after 199 days in zero gravity, the effects of returning to earth on the bodies of astronauts are numerous.
The end of a journey and the start of a physical journey. Accompanied by the Japanese Akihiko Hoshide and the Americans Shane Kimbrough and Megan McArthur, the French Thomas Pesquet made his big return to Earth, from Monday to Tuesday, aboard SpaceX's Dragon capsule, which landed off the coast of coasts of Florida (United States).
The four space heroes were extracted from the capsule on stretchers, before being brought back by helicopter to dry land.
After rapid medical tests, Thomas Pesquet took off from the United States to join the European Astronaut Center in Cologne (Germany).
He will stay there three weeks, the time to carry out a battery of scientific tests, intended to observe the effect of a long stay in orbit on the human body.
Because after six months in zero gravity, the effects of returning to Earth on the organs of astronauts are numerous.
Small review.
Why do astronauts have "earth sickness"?
On board the International Space Station (ISS), astronauts remain in zero gravity. For the body, it is as if they were "in a lying position 22 hours a day", explains Guillemette Gauquelin-Koch, head of life sciences at the National Center for Space Studies (Cnes). Returning to Earth, they regain Earth's gravity, but experience loss of balance with discomfort and vomiting. “It is the vestibular apparatus, which is in the inner ear, that gives the balance. In space, this organ no longer functions. On returning to Earth, the brain no longer knows how to manage the balance, ”explains Philippe Perrin, a former astronaut, who specifies that it takes one or two days for the balance to return completely.
That's not all.
In weightlessness, the blood remains massed in the upper part of the human body.
On returning to Earth, it suddenly falls to the lower part, causing orthostatic hypotension, that is, an excessive drop in blood pressure.
"The heart has to get back to work, pump and distribute the blood again correctly, that's why we put them back on their feet very gradually," Guillemette Gauquelin-Koch analyzes.
Not to mention that with weightlessness, the muscles of the feet no longer work either.
“There are lots of muscles in the feet that act as sensors and play on balance.
To regain balance, you have to regain contact between the arch of the foot and the ground, ”adds Philippe Perrin.
Why are the astronauts taller when they come back?
Normally, Earth's gravity pulls our bodies down.
In space, it is the reverse.
The gravity being too low to "pack the bodies" of astronauts, their spine stretches, increasing by 4 or 5 centimeters on average.
“On Earth, we gain about 1 centimeter per night, but we lose them within an hour of getting up,” explains Guillemette Gauquelin-Koch.
On returning to Earth, the astronauts regain gravity: “The column recedes a little during the descent towards the Earth, then when the astronauts stand up again, because of the weight of the vertebral discs on top of each other.
You have to be very vigilant during the recovery of the spine, there is a risk of herniated discs, ”according to Philippe Perrin, who specifies that their usual size returns after two or three days.
Why do astronauts appear thinner on their return?
Even though astronauts exercise for two or three hours a day aboard the ISS, they experience significant muscle loss, due to "extreme physical inactivity," notes Dr Gauquelin-Koch.
"In weightlessness, we restore a certain effort, but it's never like on Earth," says Philippe Perrin.
Add to that osteoporosis, that is, the decrease in bone density and changes in its micro-architecture.
“In space, there is a decalcification of the bones.
This loss of calcium returns after a year.
But bone micro-architecture never returns to normal, which can cause fractures, for example, ”says Guillemette Gauquelin-Koch.
Do astronauts have declining eyesight?
If some astronauts have no problem on their return, others have mentioned a decline in visual acuity, a phenomenon that can hardly be explained by scientists, according to the head of Life Sciences at Cnes: “The Weightlessness causes a new distribution of cerebrospinal fluid in the brain, this rise of fluids towards the head can exert pressure on the back of the eyeball.
"An unfortunately" irreversible "effect, adds the specialist.
How long does it take for them to regain physical form?
Functioning of the heart, balance, sight, bodybuilding… On returning from space, the body is put to the test.
"Everything is disturbed, there is not a single organ that is not affected", decrypts Philippe Perrin.
And for good reason, scientists estimate that a six-month journey in zero gravity represents the equivalent of ten years for certain organs.
“It is estimated that it takes 3 weeks or even a month to regain your normal physical state, it depends on each astronaut.
But the longer the trip, the longer it takes.
"According to him, Thomas Pesquet," who has an extraordinary physical form ", should quickly be back on his feet.
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