Stand on solid ground and it feels obvious that “down” points toward the center of the planet and “up” leads to the sky. Yet if space stretches in every direction, the idea of something being “beneath ...

Two astronauts in full spacesuits with backpacks on a space walk with tethers, facing each other with hands out. The astronauts are in front of planet earth and some distant stars are also visible.

Researchers have discovered chemical fingerprints of Earth's earliest incarnation, preserved in ancient mantle rocks. A unique imbalance in potassium isotopes points to remnants of “proto Earth” ...