tidally locked exo-Earth tagged posts

Comets that have hit Earth have been a mixed bag. Early in Earth’s history, during the solar system’s chaotic beginning, they were likely the source of our planet’s water, ultimately making up about 0.02% of the planet’s mass. (Mars and Venus received a similar fraction.)

Comets brought complex organic molecules and the biosphere, but later posed a threat to the same in cometary collisions...