The Moon Why does the daily moonrise time vary by as much as 60 minutes, and as little as 30 minutes during the same month?
Solar System As Earth was molten early during its formation, dense metals should have sunk toward the core, yet iron is found closer to the surface. Did asteroids and comets deliver some of these materials?
Exoplanets, Planets, Robotic Spaceflight, Solar System At the end of the Cassini mission, could the probe be put into orbit around Titan to observe it on a permanent basis?
Solar System What would happen if a comet came as close to Earth as siding spring (C/2013 A1) did to Mars, and what would it look like?
