Spending an extended period in space can have several effects on the human body due to the absence of Earth’s gravitational force. Here are some of the key changes experienced by astronauts during extended space missions:

1. Muscles and Bones: Without the constant pull of gravity, muscles and bones start to weaken. Muscle mass can decrease by up to 30% on missions longer than 2 weeks. Bones can lose 1-2% of their mass every month in space, increasing the risk of fractures.

2. Weight Loss: While weight itself doesn’t matter in microgravity, maintaining a healthy weight can be challenging. Astronauts may experience weight loss during their missions, affecting their overall health.

3. Eyesight: Changes in fluid distribution in the head can lead to eye problems, including decreased vision sharpness and structural changes in the eye. Some of these changes can be permanent.

4. Neural Adjustments: Astronauts may experience changes in brain structure and function related to motor function and orientation due to the lack of gravity.

5. Skin Sensitivity: Skin sensitivity may increase in space, and astronauts can develop rashes and other skin issues.

6. Genetic Changes: Space travel can affect DNA, leading to altered telomere length (structures at the end of DNA strands) and changes in gene expression. These genetic changes could have implications for health and aging.

7. Immune System: Astronauts’ white blood cell counts may decrease in response to radiation exposure in space.

8. Microbiome Changes: The composition of gut bacteria and fungi can change significantly during space travel, influenced by factors like diet, radiation, and altered physical activity.

It’s important to note that extensive research is ongoing to better understand these effects and develop strategies to mitigate health risks during long-duration space missions, such as those planned for future missions to Mars.