Scientists Intrigued by Strange Behavior of Distant Planet

A team of astronomers observed a confused exoplanet orbiting its two parent stars in a highly unusual way.

As New Scientist reports, the planet, which was first discovered in 2004, is located in a system called Nu Octantis 72 light-years away, and is twice the size of Jupiter. After it was spotted, some physicists thought its mere existence was impossible due to its extremely close proximity to its twin stars.

But according to a new paper published in the journal Nature, an international team of researchers is proposing a wild new theory to explain how the planet could exist while also having such an extremely tight orbit.

They propose that one of the stars and the planet orbit the second star in two opposite directions. In other words, the planet is retrograde, or orbiting the star in reverse.

"The existence of this planet has been controversial, because there were no observational precedents and we expect planets to form in prograde orbit if they form at the same time as the stars," coauthor and University of Hong Kong professor Man Hoi Lee told IFLScience.

To make matters even more unusual, the researchers propose that the planet's orbit is sandwiched between the two stars, forcing it to thread the needle during each orbit.

It's an erratic dance that highlights how much there's still to learn about the complex orbital mechanics of multi-star systems.

"It invites scientists to consider a wider range of star and planet scenarios regarding both formation and evolution," University of Texas at Arlington professor Manfred Cuntz, who was not involved in the research, told New Scientist.

One of the system's stars is a white dwarf, indicating it's nearing the end of its life cycle and making Nu Octantis an even more exotic outlier. The scientists estimate that the system was formed 2.9 billion years ago.

However, the planet came to be much later. The researchers propose that it either used to orbit both stars, and changed to its unusual trajectory after one of the stars turned into a white dwarf, or it accreted its considerable mass from said white dwarf.

But more research is needed before they can develop a more accurate picture of how the planet evolved.

"Observations of other planets in tight binary systems with late-stage or post-main- sequence stellar components will provide additional clues for us to better understand the formation and dynamical evolution of planetary systems," the team wrote in its paper.

The researchers are already excited to get a closer glimpse of a similar binary star system, such as HD 59686, which also hosts an enormous gas giant with six times the mass of Jupiter.

More on binary star systems: Alpha Centauri Sending Stream of Objects Into Our Solar System, Scientists Propose

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