Not any new planet, not yet. But pretty interesting anyhow.
STEREO, the twin spacecrafts designed to get a 3D view, and the corresponding greater understanding, of the Sun have inccidentally found something very informative not about the Sun itself but about the very far edges of its influence area, the Heliopause.
While looking at the Sun, STEREO detected uncharged atoms arriving from the far reaches beyond it. The researchers of the University of California Berkley studying the phenomenon have concluded they are actually the back tide of the charged particles (ions) that the Solar wind pushes outside. Once they reach the edge of the Solar System, they release this charge to the much colder interstellar medium and then, deprived of the electromagnetic properties that made them flow outwards as part of the Solar wind, fall back into the center of our stellar system.
The presence of these particles had been detected previously by Voyager 2 but its origins and meaning had remained a mystery till now.