Rare three-sun planet may lurk in Orion’s nose
There’s now even more evidence that a bizarre star system perched on the constellation Orion’s nose may contain the rarest type of planet in the known universe: a single world orbiting three suns simultaneously. The star system, known as GW Orionis (or GW Ori) and located about 1,300 light years from Earth, makes a tempting target for study. With three dusty, orange rings nested inside one another, the system looks like a giant bullseye in the sky. At the centre of that bullseye live three stars: two locked in a tight binary orbit with each other and a third swirling widely around the other two.
Triple-star systems are rare in the cosmos, but GW Ori gets even weirder the closer astronomers look. In 2020, researchers took a close look at GW Ori with the Atacama
Large Millimeter/submillimeter Array (ALMA) telescope in Chile and discovered that the system’s three dust rings are actually misaligned with one another, with the innermost ring wobbling wildly in its orbit.
The researchers proposed that a young planet – or the makings of one – could be throwing off the gravitational balance of GW Ori’s intricate triple-ring arrangement. If the detection is confirmed, it would be the first triple-sun planet, or ‘circumtriple’ planet, in the known universe. Research published in September 2021 offers fresh evidence of that rare planet’s existence. Scientists conducted 3D simulations to model how the mysterious gaps in the star system’s rings could have formed based on observations of other dust rings, or ‘protoplanetary discs’, elsewhere in the universe.
The team tested two hypotheses: either the break in GW Ori’s rings formed from the torque applied by the three twirling stars at the system’s centre, or the break appeared when a planet formed within one of the rings. It was concluded that there’s not enough turbulence in the rings for the stellar torque theory to work. Instead the models suggest that the presence of an enormous, Jupitersize planet, or perhaps several planets, is the likelier explanation for the rings’ strange shape and behaviour. If future observations of the system support that theory, GW Ori may be “the first evidence of a circumtriple planet carving a gap in real time,” Jeremy Smallwood from the University of Nevada, Las Vegas, said.
Sadly, a hypothetical observer on this potential planet wouldn’t actually be able to see all three suns rise and fall in the sky; the two stars at the centre of the system move in such a tight binary orbit that they would appear as one great star, with the third swooping around them. If a planet is confirmed, the mere existence of this world would prove that planets can form under a wider array of conditions than scientists previously realised. If three suns and a wobbling mishmash of dust rings aren’t enough to thwart a fledgling planet, then who knows what is.