Inclined planet in the protoplanetary disc of HD 139614 creates shifting shadows

Observations of the protoplanetary disc surrounding the star HD 139614 reveal complex light patterns caused by an inclined planet. By analyzing scattered-light images, researchers identified shifting brightness in the inner ring and a distinct spiral structure. A physical model suggests that a tilted planet forces inner parts of the disc to warp and precess, casting long-lasting shadows across the outer regions.

Star system: HD 139614 | Distance from the Sun: 436 light years

The protoplanetary disc surrounding the star HD 139614 exhibits complex light patterns, including broad shadows and asymmetrical rings. These visual structures provide evidence for the existence of an inclined planet hidden within the disc. By analyzing light reflected from dust particles in the disc across multiple time periods, the researchers identified a bright inner ring located between 13 and 21 astronomical units from the star. The brightness of this ring varies over time, suggesting the presence of a structure closer to the star, at approximately 1 astronomical unit, with changes occurring on a timescale of less than 11 months.

To understand the cause of these shadows, a physical model was constructed using equations that describe how a disc can warp or twist. The model treats the disc as three distinct rings separated by gaps, with a tilted planet positioned between the two innermost sections. This planet causes the inner rings to tilt and precess—a motion similar to the wobble of a spinning top—relative to the rest of the disc. As these rings tilt, they cast shadows across the outer, undisturbed parts of the disc. The combination of these shadows explains the dark patches seen covering roughly two-thirds of the outer disc, as well as the observed asymmetry in the ring structure.

Additional observations highlight a spiral-shaped inner arc located between 31 and 44 astronomical units from the star. This spiral is tightly wound, with a measured pitch angle of approximately 6.1 degrees. While the planet causes the inner rings to precess, the timescales for these motions are extremely long, specifically 8,400 years and 72,000 years. Consequently, the observed shadows remain effectively stationary over typical human observational timeframes, providing a stable view of the ongoing gravitational influence exerted by the unseen planet.

Key findings
An inclined planet is responsible for warping the inner sections of the HD 139614 protoplanetary disc, creating broad shadows across the outer regions.
Brightness fluctuations in the inner ring at 13 to 21 astronomical units suggest an underlying structure at approximately 1 astronomical unit, varying in under 11 months.
A tightly wound spiral structure was identified in an inner arc between 31 and 44 astronomical units with a pitch angle of 6.1 degrees.
The precession of the inner disc rings occurs over thousands of years, keeping the observed shadow patterns stable over long periods.

Scientific study

Shadows cast by precessing annuli as evidence for an inclined planet in HD 139614 (external link)