A newly discovered planet has been located orbiting three stars at the same time in a peculiar arrangement. The new world is called HD 131399Ab in the constellation Centaurus. The planet is 340 light-years from Earth, and all three stars are visible in the sky, for about half of its orbit through the system.
According to some rough calculation made by the Space.com team, it is believed the three stars would be similar in brightness to the full moon seen on Earth. It is located about 340 light years from Earth, and it is suspected to be 16 millions years old, one of the youngest exoplanets studied to date. The triple-sun world has temperatures of 1.070 degrees Fahrenheit (580 degrees Celsius), and surprisingly for the non-scientist community, is one of the coldest and least massive directly imaged exoplanets. HD 131399Ab is estimated to have 4 Jupiter masses.
The planet was discovered by a team of astronomers led by the University of Arizona, and the study will be published online in the journal Science Thursday, 7 July 2016.
The exoplanet was detected by a first-year doctoral student and the paper’s first author, Kevin Wagner. Wagner is part of Daniel Apai’s team, who is an assistant professor of Astronomy and Planetary Sciences, leader of a research group dedicated to finding and observing exoplanets in the University of Arizona.
Wagner told Space.com that the planet is orbiting star A and stars B and C orbit HD 131399Ab and star A. He explained that much of the planet’s year, the three stars seem close together, and they give a familiar nightside and dayside with a triple sunset and three sunrises each day.
What has surprised scientist is that the triple-star system has a large orbit around star A, making it the widest orbit ever studied in a triple-star system. Wagner also said that star B and C orbit extremely close to star A, which makes their gravity a very significant aspect to the new planet. In other triple star systems, the planet orbits closely to one star and much farther away from the other 2.
Wagner added to his statement to Space.com that the triple-star system is the first one that they have ever found that looks like that and its images tell them that planets can exist in much more exotic configurations, in multiple star systems, than many scientists would have thought possible.
HD 131399Ab orbits Star A at a distance of about 82 astronomical units. An astronomical unit is a distance from the Earth to the sun, which is 93 million miles (150 million kilometers). This means that the new exoplanet orbit to around star A is about twice the average distance from the sun to Pluto, according to Space.com. The difference with Earth is that star A is larger and brighter than the sun – about 80 percent more massive and 7.8 times more luminous – and star A’s light is looked from the new planet as moonlight due to the wide orbit.
The science portal makes another comparison to understand the star A’s light impact on HD 131388Ab. It says that the surface of Pluto, the sun at high noon delivers about as much light as the Earth gets just after sunset. On the exoplanet, Star A would provide nearly twice that light.
Regarding star B and C, they are smaller than star A, also dimmer. Star B is about 0.87 times as bright as the sun and has almost the same mass. Star C is about 60 percent the sun’s mass and only 0.17 time as bright.
Space.com says that as the planet orbits and the stars distanced each other, they reach a point where the setting of one coincides with the rising of the other 2. At that moment the planet is in nearly constant daytime for about 140 Earth-years, which is one-quarter of its orbit.
The researchers found water and methane in HD 131399Ab’s atmosphere and similar to Jupiter and Saturn, it also has hydrogen and helium, predominantly.
According to National Geographic, Wagner says that unlike the distinct clouds swirling on Jupiter, this new world is remarkably cloud-free. He says that the planet seems to be clear-partly cloudy at most, and he described how clouds of silicate rock particles could be forming deep within the planet’s atmosphere. Wagner added that at even lower layers, the temperature would be hotter, and iron droplets may condense out of the warm atmosphere, forming iron rain.
Discovering HD 131399Ab with direct imaging
Other planet-discovering techniques look for planets through indirect means, like gravitational tugs or silhouettes. But the triple-star planet was discovered using a different method: direct imaging. Direct imaging is a technique in which light from the planet is seen directly by a telescope.
The discovery was possible thanks to the advanced, direct imaging telescope known as Spectro-Polarimetric High-Contrast Exoplanet Research Instrument (SPHERE), which is located on the European Southern Observatory’s Very Large Telescope in the Atacama Desert, in Chile.
SPHERE can detect heat signatures of hidden exoplanets through its sensitivity to infrared light. Wagner told Science.com that the telescope uses a technique that boosts the contrast of its images, which, in turn, correct the blurring effects of Earth’s atmosphere and blocks unwanted starlight.
Space says that the following step after the discovery is to study the planet’s orbit to determine the long-term stability of the triple-star system.