A planet is not self-luminous. It reflects starlight. Its own gravity pulls a planet into its most stable shape, a slightly flattened sphere.
Exoplanets are detected by observing their star's "wobble" which the exoplanet's gravitational attraction causes.
Scientists have spied a new exoplanet and not only is it the biggest one yet, but it’s also moving in the wrong direction
Unlike other planets, which orbit in the same direction as their stars rotate, "WASP-17" moves in the opposite way, according to a study published in Astrophysical Journal.
Instead of traveling around its host star in the same direction the star spins, like all other known planets, but this abnormal planet is orbiting backwards. Scientists think the renegade orb, named WASP-17, got flipped around during a near collision with another planet during its early development.
Planets are born from the same ball of rotating gas that creates their parent star, which is why they usually orbit, and spin, in the same direction as their "mother star". While WASP-17 is the first planet known to orbit backwards, some planets in our own solar system; such as, Venus, are spinning backwards. Like WASP-17, Venus may have experienced some kind of collision during its early history, which threw it into an unusual spin.
Researchers at South African Astronomical Observatory discovered the new exoplanet 1,000 light years away from Earth. In addition to its surprising orbit, the exoplanet stands out because of its size; in that, being only half the mass of Jupiter but twice its volume, the researchers claim WASP-17 is now the largest known planet.
WASP-17 marks the 17th exoplanet discovered by the Wide Angle Search for Planets, or WASP project, conducted by eight universities in the U.K.
Because exoplanets don’t give off any light of their own and are usually obscured by their super-bright host stars, the scientists find exoplanets by scanning hundreds of thousands of stars, looking for the subtle dimming that occurs when a planet passes in front its parent star.
The result is that Venus and Mercury are the two inferior planets of the solar system.
They probably represent planetesimals that failed to form a planet.
The superior planets are Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.