The ALMA radio telescope array captured this image of a protoplanetary disc around the star GW Orionis. Three dust rings are clearly visible with the innermost ring face on to the observer. The outer rings appear oval because they are tilted with respect to the inner ring. Image: ALMA (ESO/NAOJ/NRAO), Bi et al., NRAO/AUI/NSF, S. Dagnello
Planets orbiting single stars like the Sun are commonplace, and dozens of planetary systems have been found around double stars. But no confirmed planets have been seen to date orbiting triple stars.
To study that possibility, astronomers using the Atacama Large Millimeter/submillimeter Array examined a young triple star system known as GW Orionis featuring two stars just an astronomical unit apart – the distance from Earth to the Sun – and a third companion eight times farther out.
The observations revealed three huge dust rings 46, 188 and 336 au from the central stars (or comparison, Neptune orbits the Sun at a distance of 30 au). Estimates of the amount of dust in the rings are 75, 170 and 245 Earth masses, enough to form the “seeds” of giant planets.
As it turns out, the innermost ring is steeply tilted with respect to the ...