WASP-156 b’s orbit is aligned, not polar, new data show

Star system: WASP-156 | Distance from the Sun: 397 light years

WASP-156 b is a short-period exo-Neptune, a planet similar in size to Neptune but much closer to its star. Scientists studied the planet’s orbit using new high-precision spectroscopic and photometric observations. They measured the Rossiter-McLaughlin effect, which reveals the angle between the planet’s orbit and the star’s rotation. The results show that WASP-156 b’s orbit is well aligned with the star’s equator, with a projected obliquity of about minus eight degrees, contradicting earlier reports of a highly tilted, or polar, orbit.

The team also found that the star rotates more slowly than previously thought, which helps explain why earlier studies may have suggested a polar orbit. Updated measurements show the star’s projected rotational velocity is less than two kilometers per second. The planet’s orbit is nearly circular, and there are no massive Jupiter-like planets nearby, based on long-term radial velocity data. These findings suggest that WASP-156 b either formed in its current location or migrated there early in its history, rather than being moved by later gravitational interactions.

This study moves WASP-156 b from a group of close-in Neptunes thought to have polar orbits to the group of aligned Neptunes, providing new insights into how such planets form and evolve.

Key findings
- WASP-156 b’s orbit is aligned with its star’s equator, not polar.
- The star rotates more slowly than previously reported.
- The planet’s orbit is nearly circular, with no nearby massive companions.
- Results support in situ formation or early migration for WASP-156 b.
- The findings clarify the planet’s place among close-in Neptunes.

Scientific study

The Neptunian ridge planet WASP-156 b does not have a polar orbit (external link)