Planet the Sun: Jupiter is the largest, at 318 Earth masses, whereas Mercury is the smallest, at 0.055 Earth masses. The planets of the Solar System can be divided into categories based on their composition: An exoplanet (extrasolar planet) is a planet outside the Solar System. In early 1992, radio astronomers Aleksander Wolszczan and Dale Frail announced the discovery of two planets orbiting the pulsar PSR 1257+12. This discovery was confirmed, and is generally considered to be the first definitive detection of exoplanets. These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the
The Secret of the Ninth Planet The Secret of the Ninth Planet The Secret of the Ninth Planet is a science-fiction novel written by Donald A. Wollheim and first published in the United States in 1959 by the John C. Winston Co. Wollheim takes his heroes on a grand tour of the solar system as that team struggles to prevent an alien force from blowing up the sun. This is the last of three juvenile novels that Wollheim wrote for Winston, the other two being "The Secret of Saturn's Rings" and "The Secret of the Martian Moons". This is one of the thirty-five juvenile novels that