Having three stars is a big deal for an exoplanet. People are used to Earth just having one so having two more as part of a system is certainly remarkable. But how did HD 131399Ab evolve to become what it was today?
According to Kevin Wagner, who led the team of researchers who discovered the exoplanet, there are three possible scenarios that could help explain how HD 131399Ab came to have three stars.
First, the planet was originally formed in a spot much closer to the star it is orbiting. However, it is now in long orbit because it was flung into that position by an undetermined process, which may or may not have involved planets that are unseen.
Second, the star HD 131399Ab orbits first formed near one of the twin stars. However, it too was flung out, catching the orbit it follows now.
Lastly, Wagner and his team say that the exoplanet's stars could have been formed someplace else and were shoved into place thanks to some stellar shuffling.
"We think it's unlikely that the planet formed where we see it today," said Wagner.
When the researchers discovered HD 131399Ab, they deduced that it orbits around its stars once in every 550 Earth years. However, as the planet moves, the stars move farther apart each day until a point is reached where one of the twin stars rises as the other sets, which results in almost constant daytime for about 140 Earth years.
HD 131399Ab is located in the Centaurus constellation some 340 light-years away from Earth. It is estimated to be four times the size of Jupiter, has an orbit about twice as large as Pluto's and features significant amounts of methane and water. It is also one of the coldest to be ever directly detected, with a temperature of roughly 1,000 degrees Fahrenheit, but this is still too hot for the planet's water to remain in liquid form.
It was Wagner who identified HD 131399Ab among hundreds of other candidate planets, also leading the follow-up investigation to verify its nature.
HD 131399Ab marks the first exoplanet discovery via Spectro-Polarimetric High-Contrast Exoplanet Research Instrument (SPHERE), one of the world's most powerful instruments designed to find planets around other stars. Operated as part of the European Southern Observatory's Very Large Telescope in Chile's Atacama Desert, SPHERE is sensitive to infrared light, which is what makes it capable of detecting heat signatures coming from young planets.