HAT-P-26b

Lore & Background

HAT-P-26b was detected in 2010 by the HATNet Project, which identified it as the 26th star found to host a planet by that survey. The planet is thought to have formed via pebble accretion. Its transmission spectrum, taken in 2015, favored either a cloudless atmosphere or one with a low-lying cloud deck. In 2019, the atmospheric composition was measured, revealing a water vapor volume fraction of 1.5%, a carbon-depleted composition with a C/O ratio below 0.33, and the presence of light metal hydrides. The planet's measured temperature is 563 K.

Transit-timing variations (TTVs) were detected in 2019, initially with an unclear cause. By 2023, additional data suggested the TTVs might be due to a second planet. In 2024, a candidate second planet, about twice the size of Earth and slightly farther from the star than HAT-P-26b, was detected in TESS data, though it requires further observations for full confirmation. A 2015 survey found no stellar companions, though a red dwarf companion on a wide orbit is suspected.

Reader's Guide

HAT-P-26b holds significance as a well-characterized hot Neptune, providing insights into planetary formation and atmospheric composition. Its detection of water vapor at a specific volume fraction and a low carbon-to-oxygen ratio informs models of planet formation via pebble accretion. The presence of light metal hydrides in its atmosphere adds to the chemical inventory of exoplanet atmospheres. The unresolved transit-timing variations and the candidate second planet highlight the system's potential for further discoveries, including a possible Earth-sized companion. The planet's inclusion in the NameExoWorlds project, where it was named Guataubá, reflects its cultural and scientific importance, linking astronomical discovery with Taíno mythology. Its legacy lies in advancing the study of Neptune-sized exoplanets and their atmospheres, while the ongoing investigation of TTVs and a second planet candidate keeps the system a focus for future observations.

Did You Know?

• The planet's atmosphere contains water vapor at a volume fraction of 1.5% and light metal hydrides.
• A candidate second planet, about twice Earth's size, was detected in TESS data in 2024 but needs confirmation.
• The star HAT-P-26 is named Guahayona and the planet Guataubá, after figures from Taíno mythology.