Astronomers are closing in on one of the most tantalizing possibilities in planetary science, evidence that a previously ...

Scientists believe there may be a huge planet sitting at the far reaches of the solar system. Since new evidence of Planet 9's existence emerged a few years ago, experts have been weighing in on how ...

The "alien mothership" hypothesis for interstellar comet 3I/ATLAS is about to have a key test, as it hits solar conjunction and perihelion. What does that mean, and why is a Harvard professor of ...