Outflowing atmosphere of exoplanet WASP-12b reveals complex tidal tail structure

Star system: WASP 12 | Distance from the Sun: 1347 light years

The ultra-hot Jupiter WASP-12b is leaking gas into space, forming a structure that does not follow the planet's orbit. By observing the planet as it passes in front of its host star, researchers detected hydrogen-alpha light—a specific signature of hot hydrogen gas—that reveals how the atmosphere escapes the planet's gravitational control and shears into long tidal tails.

Using high-resolution transit spectroscopy, which measures how light is filtered through an atmosphere, the study identified a strong hydrogen-alpha signal. This signal persisted for at least 30 minutes after the planet finished its transit across the star, indicating that the escaping material creates a trailing cloud of gas.

The findings show that this escaping gas moves in the reference frame of the host star rather than the planet itself. Previous observations dating back to 2012 also show this behavior when analyzed correctly. A new three-dimensional computer model confirms that this motion is a natural result of the planet being so close to its star that its atmosphere is being stripped away.

Key findings
- Detection of excess hydrogen-alpha absorption of 3.29 percent during and after the transit of WASP-12b.
- The escaping gas does not move with the planet, but instead remains largely in the stellar reference frame.
- The atmospheric signal is slightly redshifted by 5.4 kilometers per second.
- A three-dimensional model shows that gas quickly shears into tidal tails after escaping the planetary Roche lobe.
- Re-analysis of data from 2012 confirms that this escape behavior has been present for over a decade.

Scientific study

WASP-12b Exhibits Persistent In-Transit Hα Absorption (external link)