Mercury, Venus, and Mars sit within the same general neighborhood as Earth, yet each has followed a radically different path. One kept a magnetic field against the odds. Another trapped so much heat ...

Astronomers are closing in on one of the most tantalizing possibilities in planetary science, evidence that a previously unknown world may be lurking in the outer reaches of the solar system. The ...

Illustration comparing the planets of the Solar System and the Sun on the same scale. The planets are shown to scale relative to each other but their distances are not. From left to right the bodies ...