Agnirva Space Premier League - Expedition #32570: One Twin in Space, One on Earth: What Happens to the Human Body?

The Human Exploration Research Opportunities (HERO) experiment studying differential effects on homozygous twin astronauts is one of the most iconic space biology investigations to date. This study, supported by NASA and involving a consortium of leading scientists across multiple institutions, aimed to understand how spaceflight uniquely alters the human body by studying identical twins—one in space and one on Earth.

One of the twins, astronaut Scott Kelly, spent nearly a year aboard the ISS during Expeditions 43 through 46, while his identical twin, Mark Kelly, remained on Earth. Their identical genetics created a perfect natural control for analyzing how spaceflight changes health, biology, and cognition.

The research explored numerous factors: gene expression, immune response, microbiome changes, cognitive function, vision changes, and telomere dynamics. Scientists observed significant changes in Scott's body during and after flight—many of which returned to baseline post-mission, while others persisted, indicating long-term effects.

Key findings included changes in gene expression related to immune response and DNA repair, shifts in gut microbiota, and notably, the elongation of Scott’s telomeres in space (contrary to expectations). Cognitive performance also declined slightly in space, but returned to normal after landing.

This experiment is a milestone in space medicine. It informs how long-term space missions—like those to Mars—might impact astronauts, guiding medical preparations, countermeasures, and mission planning. The study also illustrates the importance of personalized medicine in space exploration.

By examining the same genetic blueprint in two drastically different environments, scientists have taken a major leap in understanding human adaptation to space—a critical piece of the puzzle for our journey into the cosmos.

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