1. The problem statement, all variables and given/known data A 26 year-old biologist makes a trip to study alien life forms in a distant planet 10 light-years away. The round trip including a stay of 1 year in the distance planet takes 21.5 years according to the clock on earth. The biologist’s son is 3 year-old when she left. Assume that the planet is not moving with respect to earth, and the speed is the same for both outbound and inbound part of the journey. What is the difference in age between the mother and son after she returns back to earth? 2. Relevant equations T' = T √(1-(v2 /c2)) 3. The attempt at a solution A. 7.0 years B. 16.8 years C. 23.0 years D. 30.0 years E. 37.0 years The answer is 7 years according to the solution manual. I tried to find the speed of the astronaut, then plugged it in to the relevant equation. I'm not sure how to find the speed of astronaut actually. I think I have to solve for the reference frame of the astronaut T, as T' is the frame of earth.