Solar System is not round

Most of us would know that the Solar System is round, in a sense the Sun is the center while the planets and other objects rotates around the Sun in a circular orbit. Well, at least until now some reports that according to two spacecrafts travelling far away in deep space, reports that the Solar System is not round. So what is the reason? I am unable to explain it since I am only an novice astronomer. You could try your luck at space.com where you get to read reports and hopefully answers that are simple to understand.