One Twin Spent 340 Days in Space. Then NASA Compared Them

In 2015, NASA sent astronaut Scott Kelly to the International Space Station for 340 days, while his identical twin brother Mark stayed on Earth. Then ten research teams compared them: the tips of Scott's chromosomes grew longer in space and shrank back within two days of landing, and six months later 811 of his genes still weren't behaving the way they did before. In this video we follow the NASA Twins Study day by day: what a year without gravity does to your height, bones, muscles, heart and eyes, why coming home hurt more than leaving, how astronauts from Colorado State, climbers on Everest and the four civilians of Inspiration4 confirmed the results, why "space changed his DNA" is a myth, and what gravity is doing to your own body right now. Every claim is backed by the original studies listed below. CHAPTERS 0:00 340 days apart 0:45 The missing copy 1:22 The twins 2:30 The height game 3:34 A year without gravity 5:31 Coming home 6:17 Just one man? 7:18 Three days, four strangers 8:26 The part nobody tells you 9:32 The twist SOURCES (all sources always cited) Garrett-Bakelman et al., "The NASA Twins Study: A multidimensional analysis of a year-long human spaceflight", Science 364, eaau8650, 2019: https://www.science.org/doi/10.1126/s... NASA, "NASA's Twins Study Results Published in Science Journal", 2019: https://www.nasa.gov/humans-in-space/... NASA, "NASA Twins Study Confirms Preliminary Findings" (with the March 2018 statement on Scott Kelly's DNA): https://www.nasa.gov/humans-in-space/... NASA, "NASA Astronaut Scott Kelly Returns Safely to Earth after One-Year Mission", 2016: https://www.nasa.gov/news-release/nas... NASA, "One if by Land, Two if by Space: Astronaut Twins Tantalize Human Research Possibilities in Spaceflight", 2013: https://www.nasa.gov/missions/station... NASA, "NASA, Roscosmos Assign Veteran Crew to Yearlong Space Station Mission", 2012: https://www.nasa.gov/news-release/nas... Scientific American, interview with Scott Kelly, 2019: https://www.scientificamerican.com/ar... Scott Kelly, "Endurance: A Year in Space, a Lifetime of Discovery" (Knopf, 2017) CNN, 3 March 2016: https://www.cnn.com/2016/03/03/us/ast... and NPR, 4 March 2016: https://www.npr.org/transcripts/46916... NASA, "What is your space height?": https://www.nasa.gov/wp-content/uploa... and Chang et al., Spine, 2016: https://pubmed.ncbi.nlm.nih.gov/27779... Reilly, Tyrrell & Troup, "Circadian variation in human stature", Chronobiology International, 1984: https://pubmed.ncbi.nlm.nih.gov/6600017/ NASA Astrobiology, "Gravity Hurts (So Good)": https://astrobiology.nasa.gov/news/gr... NASA, "Risk of Spaceflight-Induced Bone Changes": https://www.nasa.gov/reference/risk-o... and Lang et al., Journal of Bone and Mineral Research, 2004: https://pubmed.ncbi.nlm.nih.gov/15125... Gopalakrishnan et al., Aviation, Space, and Environmental Medicine, 2010: https://pubmed.ncbi.nlm.nih.gov/20131... MacNamara, Levine et al., Circulation, 2021 (UT Southwestern): https://www.utsouthwestern.edu/newsro... NASA, "Risk of Spaceflight Associated Neuro-ocular Syndrome (SANS)": https://www.nasa.gov/reference/risk-o... Luxton et al., "Temporal Telomere and DNA Damage Responses in the Space Radiation Environment", Cell Reports, 2020: https://pubmed.ncbi.nlm.nih.gov/33242... Luxton et al., "Telomere Length Dynamics and DNA Damage Responses Associated with Long-Duration Spaceflight", Cell Reports, 2020: https://pubmed.ncbi.nlm.nih.gov/33242... Jones et al., Nature, 2024 (Inspiration4 crew): https://pmc.ncbi.nlm.nih.gov/articles... Garcia-Medina et al., 2024 (telomeres in the Inspiration4 crew): https://pmc.ncbi.nlm.nih.gov/articles... Mason et al., "A second space age spanning omics, platforms and medicine across orbits" (Space Omics and Medical Atlas), Nature, 2024: https://pmc.ncbi.nlm.nih.gov/articles... NASA, Bed Rest Studies FAQ: https://www.nasa.gov/hrp/bedrest-faqs/ and Ploutz-Snyder et al., Medicine & Science in Sports & Exercise, 2018: https://pmc.ncbi.nlm.nih.gov/articles... Time dilation: our own calculation from the station's speed (about 7.66 km/s) and altitude (about 400 km) over 340 days, about 8 milliseconds; compare https://www.jeffreybennett.com/scott-...