Astronomer: In most cases in which a planet has been detected orbiting a distant star, the planet' s orbit is distinctly oval, whereas the orbits of Earth and several other planets around our sun are approximately circular  However, many comets orbiting our sun have been thrown into oval orbits by close encounters with planets orbiting our sun
So some of the planets in oval orbits around distant stars were probably thrown into those orbits by close encounters with other planets orbiting the same stars
In most cases in which planets have been discovered orbiting a distant star, more than one planet has been found orbiting the star.