# HAT-P-26b: A Neptune-Mass Exoplanet with a Well Constrained Heavy Element Abundance

## TL;DR

This study analyzes the atmosphere of the Neptune-mass exoplanet HAT-P-26b using space telescope data, revealing its primordial composition and providing insights into planet formation and atmospheric metallicity.

## Contribution

It presents the first detailed atmospheric metallicity measurement of HAT-P-26b, linking water abundance to heavy element content in a Neptune-mass exoplanet.

## Key findings

- Detected prominent H2O absorption bands in the atmosphere.
- Measured atmospheric heavy element content as approximately 4.8 times solar.
- Indicates the atmosphere is likely primordial with late gas accretion.

## Abstract

A correlation between giant-planet mass and atmospheric heavy elemental abundance was first noted in the past century from observations of planets in our own Solar System, and has served as a cornerstone of planet formation theory. Using data from the Hubble and Spitzer Space Telescopes from 0.5 to 5 microns, we conducted a detailed atmospheric study of the transiting Neptune-mass exoplanet HAT-P-26b. We detected prominent H2O absorption bands with a maximum base-to-peak amplitude of 525ppm in the transmission spectrum. Using the water abundance as a proxy for metallicity, we measured HAT-P-26b's atmospheric heavy element content [4.8 (-4.0 +21.5) times solar]. This likely indicates that HAT-P-26b's atmosphere is primordial and obtained its gaseous envelope late in its disk lifetime, with little contamination from metal-rich planetesimals.

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Source: https://tomesphere.com/paper/1705.04354