Are planets in the solar system that are closer to the Sun older than the ones further away? – Gavriel, age 10, Paducah, Kentucky A cloud of collapsing gas created our Sun, the first thing to form in ...

When you buy through links on our articles, Future and its syndication partners may earn a commission.

Planets larger than Earth but smaller than Neptune are the most common kind in the galaxy, but because our solar system lacks such a planet, scientists don’t know much about how they form. Astronomers ...