Can we call Pluto and Charon a binary system?

Can we call Pluto and Charon a binary system?

The debate about whether Pluto is a dwarf planet or not is still rattling, but thanks to a new series of images, we can offer a different definition for Pluto.

Can we call Pluto and Charon a binary system?

A series of images of the system Pluto-Charon, made by NASA spacecraft

While NASA’s New Horizons spacecraft continues its epic journey to the outer part of the solar system, its goal is the Kuiper Belt is getting brighter and clearer. With a mission camera called the Long Range Reconnaissance Imager (LORRI), this new series of images shows that Pluto and its largest satellite, Charon, are locked in a hard orbital dance, separated by just 11,200 miles. For comparison, the orbital separation of the Earth-Moon system is about 240,000 miles.

"A sequence of images showing how Charon revolves around Pluto set a record as the closest photograph of Pluto: it was taken from a distance 10 times shorter than from Earth," said Alan Stern, a senior researcher at the New Horizons mission from the South-West Research Institute. Boulder Institute, Colorado.

We had fuzzy images of both Pluto and Charon, but this animation shows something more.

Within 5 days, LORRI camera made 12 images of the Pluto-Charon system, tracing Charon’s full orbit. At this time, the New Horizons mission was located from 267 million to 262 million miles from Pluto. However, in addition to the rotation of Charon around Pluto, there were obvious fluctuations in the position of Pluto itself. Charon's mass, which reaches 12 percent of the mass of Pluto, has a powerful gravitational effect on Pluto. Thus, both the masses of the planets revolve around an imaginary point, called the center of gravity of the Pluto-Charon system.

Can we call Pluto and Charon a binary system?

An animation of Charon's motion around Pluto. Both objects rotate around a common center of mass.

This phenomenon is unique to any planetary object in the solar system. This fact alone raised the call to recognize Charon as an autonomous planetary body or rename the Pluto-Charon system into a “dual planetary system”.

In one of the articles written in 2012, Ray Willard explored this possibility, pointing out that the other 4 satellites discovered around Pluto have an orbit not only on this planet. They rotate around the barycenter of Pluto and Charon, the center of mass of the Pluto-Charon system. That is, they are not only Pluto satellites, but also Charon.

However, the international body that determines the celestial qualification has not yet made any decision. The International Astronomical Union (IAC) is likely to reconsider the case of Pluto and Charon after the New Horizons mission takes close-up photos of this system.

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