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 ...

Only two spacecraft have ever truly escaped the solar system, slipping beyond the Sun’s protective bubble into interstellar space. Their measurements are now reshaping how I understand the heliosphere ...

The search for an unknown planet in our solar system has inspired astronomers for more than a century. Now, a recent study suggests a potential new candidate, which the paper’s authors have dubbed ...