Our early conceptions of planets orbiting perfectly around the Sun might need to be slightly revised. While the Sun is unquestionably dominant in our Solar System, a fresh look at planetary motion highlights an interesting detail: Earth isn't actually orbiting the Sun.
The reason for this update is the barycenter, the center of mass in an orbiting body system. Imagine a cosmic playground where the Sun and Earth serve as the fulcrum around which both objects balance and rotate. This point, known as the barycenter, is not fixed within the Sun.
Although the Sun is the heavyweight champion of our Solar System, it doesn't always claim the barycenter as its throne. The immense mass of the Sun pulls Earth into its orbit, but according to Newton's law of universal gravitation, this attraction is a two-way street. Earth, in its own small way, exerts a gravitational pull on the Sun too.
While Earth's tug is negligible compared to the Sun's grip, it's enough to nudge the barycenter slightly. This point typically resides very close to the Sun's center but not always. The influence of giant planets like Jupiter and Saturn can occasionally pull the barycenter outside the Sun's boundaries.
NASA explains, "Kepler's third law describes the relationship between the masses of two objects mutually revolving around each other and the determination of orbital parameters."
NASA further elaborates, "Consider a small star in orbit about a more massive one. Both stars actually revolve about a common center of mass, which is called the barycenter. This is true no matter what the size or mass of each of the objects involved. Measuring a star's motion about its barycenter with a massive planet is one method that has been used to discover planetary systems associated with distant stars."
Due to the Sun's immense mass, the barycenter usually lies very close to, but not necessarily within, the Sun's center. The influence of giant planets like Jupiter and Saturn can occasionally pull the barycenter outside the Sun. Therefore, Earth's orbit is more accurately described as a path around this shared center of mass, rather than strictly around the Sun itself.
"Planets orbit the Sun in general terms," Planetary astronomer Dr James O'Donoghue explains on X (Twitter), "but *technically* they don't orbit the Sun alone because the gravitational influence of (mainly) Jupiter means planets must orbit a new point in space."
"The planets do orbit the Sun of course, we are just being pedantic about the situation," he added. "The natural thinking is that we orbit the Sun's center, but that very rarely happens, i.e. it's very rare for the solar system's center of mass to align with the Sun's center."
