A very peculiar system of a planet rotating around three suns has recently been discovered by a team of astronomers at the University of Arizona. The planet is known as HD 131399Ab and is unlike any other previously discovered with its orbit around three Stars. Usually, orbits such as these are highly unstable but this one is distinct in the aspect that it forms a very stable orbit around its stars.
Located at the constellation of Centaurus, the planet is 320 light-years away from the Earth, and is believed to be one of the youngest planets discovered to date with its age being about 16 millions years old. The temperature at the surface of the planet is relatively colder for an exoplanet at 580 Degree Celsius ( 850 kelvins or 1,070 F ). Also, the mass of this planet equals four times that of the Jupiter which makes it one of the least massive exoplanets directly imaged.
The reveal of this planet also marks the first discovery of an exoplanet carried out by SPHERE (Spectro-Polarimetric High-Contrast Exoplanet Research) Instrument on the Very Large Telescope ( VLT). Making the use of the sensitivity of the SPHERE to the infrared light, young planets can be discovered efficiently by blocking out the blinding lights of the host stars and also correcting the atmospheric disturbances.
For the 550 Earth years, this planet completes half of its orbit and during this time, the three stars are visible in the planet’s sky. Two of the stars appear faint and these two are much closer to each other than the third one. Also, another remarkable feature of this particular system is that the apparent distance between the two stars and the third also (which is the brightest) keeps on changing.
The observations and the simulations suggest that the brightest star is about eighty percent the mass of our Sun, it is called HD 131399A and is orbited not only by the planet but also two other stars B and C at about 300 Astronomical Unit ( 1 AU = the average distance between the Sun and the Earth). While this happens, B and C twirl around each other and the two are separated by the distance equal to that between the Earth and the Saturn. The planet travels around the star with the orbital radius of 80 AU which is twice as large as that of Pluto’s. Because these observations are based on the simulations, authors report that a variety of orbital radii are possible.
“If the planet was further away from the most massive star in the system, it would be kicked out of the system,” explained Daniel Apai, an assistant professor of Astronomy and Planetary Sciences at the University of Arizona. “Our computer simulations showed that this type of orbit can be stable, but if you change things around just a little bit, it can become unstable very quickly.”
The significance of studying the planets in the multi-star system is that studying these planets can provide great insights into how planets are formed, how they function in different star systems and thus result in the discoveries of exotic multi-star system a phenomenon. Though, if finding out about this unique system fascinated you, you must know that systems like this ones are more numerous than you think, in fact, there are as many multi-stars systems as there are ones with the single stars.
ScienceSwitch 
This is surprising to me. I didn’t realize planets in binary or trinary systems could have stable orbits so far out. Seems like you could easily fit an Earth-like planet into the habitable zone of star A.
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Our knowledge of the universe is just beginning with so many new discoveries. NASA’s mission to Jupiter is going to give us a new look at Jupiter. Thanks for the information about the newly discovered planet.
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