HAT-P-26b: A Neptune-mass exoplanet with a well-constrained heavy element abundance
American Association for the Advancement of Science
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 micrometers, 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 525 parts per million in the transmission spectrum. Using the water abundance as a proxy for metallicity, we measured HAT-P-26b’s atmospheric heavy element content (Embedded Image 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.
Support for this work was provided by NASA through grants under the HST-GO-14260 program from the STSci. H.R.W. acknowledges support from the NASA Postdoctoral Program, administered by Universities Space Research Association through a contract with NASA. Several authors acknowledge funding from the European Research Council under the European Union Seventh Framework Program: D.K.S., T.K., N.N., and T.M.E. under grant 336792; E.D.L. under grant 313014; and P.T. and D.S.A. under grant 247060-PEPS.
This is the author accepted manuscript. The final version is available from American Association for the Advancement of Science via the DOI in this record.
Vol. 356, pp. 628 - 631