The first exoplanetary family system gets a new addition! In 2010, astronomers announced that they had discovered a fourth planet orbiting the star HR 8799. Called HR 8799 e, it's closer in than the previously-known three planets, orbiting the star at a distance of about 2.2 billion km (1.3 billion miles) - roughly the same distant of Uranus from the Sun.
The planet has a mass of about 7 times that of Jupiter, though that's an estimate; it depends on the age! The planet is still glowing with the leftover heat of its formation, and the brightness depends on both its mass and its age. Since the age isn't exactly known, the mass can only be estimated.
Interestingly, the authors of the discovery paper
note that current planet formation computer models can't make planets like this at the distance of HR 8799 e from its parent star. Either the models are wrong, or the planet formed farther out from the star and moved inwards; the latter is something that is fairly certain to happen when planets are young.
Either way, this new discovery adds excitement to the new field of exoplanet hunting, as well as those who are scratching their heads trying to figure out how these planets form.