Astronomers have made a groundbreaking discovery using data from the NASA/ESA/CSA James Webb Space Telescope, shedding light on the mysterious case of the inflated exoplanet WASP-107 b. The findings, which were also supported by earlier observations from the NASA/ESA Hubble Space Telescope, have revealed crucial insights into the composition and internal dynamics of this warm gas-giant exoplanet.
WASP-107 b, often referred to as a “warm Neptune,” has puzzled scientists due to its unusually large size in comparison to its relatively low mass. However, two independent research teams have now put forth a compelling explanation for the planet’s enigmatic characteristics.
The study, published in the journal Nature, unveils that WASP-107 b’s unexpectedly high temperature is attributed to tidal heating caused by its slightly non-circular orbit. This tidal heating effect, combined with the planet’s internal dynamics, has led to the inflation of the exoplanet, providing a plausible explanation without resorting to extreme theories of its formation.
Lead author Luis Welbanks from Arizona State University (ASU) expressed, “Based on its radius, mass, and age, we thought WASP-107 b had a very small, rocky core surrounded by a huge mass of hydrogen and helium. But it was hard to understand how such a small core could sweep up so much gas, and then stop short of growing fully into a Jupiter-mass planet.”
The research teams utilized Webb’s extraordinary capabilities to measure light passing through exoplanet atmospheres, enabling them to detect and measure the abundances of various molecules, including water vapor, methane, carbon dioxide, and more. Surprisingly, the observations revealed a significant lack of methane in WASP-107 b’s atmosphere, indicating a much hotter interior than previously estimated.
This transmission spectrum, captured using the NASA/ESA/CSA Hubble and James Webb space telescopes, shows the amounts of different wavelengths (colours) of starlight blocked by the atmosphere of the gas-giant exoplanet WASP-107 b .
The spectrum includes light collected over four separate observations using a total of three different instruments: the NASA/ESA Hubble Space Telescope’s WFC3 (0.8–1.6 microns), Webb’s NIRCam (2.4–4.0 microns and 3.9–5.0 microns), and Webb’s MIRI (5–12 microns). Each set of measurements was made by observing the planet–star system for about 10 hours before, during, and after the transit as the planet moved across the face of the star.
By comparing the brightness of light filtered through the planet’s atmosphere (transmitted light) to unfiltered starlight, it is possible to calculate the amount of each wavelength that is blocked by the atmosphere. Since each molecule absorbs a unique combination of wavelengths, the transmission spectrum can be used to constrain the abundances of various gases.
This spectrum shows clear evidence for water (H2O), carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), sulphur dioxide (SO2), and ammonia (NH3) in the planet’s atmosphere, allowing researchers to estimate its interior temperature and the mass of its core.
This wavelength coverage from optical to mid-infrared is the broadest of any exoplanet transmission spectrum to date, and includes the first reported detection of ammonia in an exoplanet atmosphere.
[Image description: Transmission Spectrum of Hubble WFC3 Grism Spectroscopy; Webb NIRCam Grism Spectroscopy; Webb MIRI Low-Resolution Spectroscopy showing a graph of Amount of Light blocked vs. Wavelength of Light, with peaks for water, carbon dioxide, carbon monoxide, methane, sulfur dioxide, and ammonia labeled. ]
Credit:
NASA, ESA, CSA, R. Crawford (STScI)
The findings have not only provided a new understanding of WASP-107 b but also offer insights into the puffiness of numerous low-density exoplanets, addressing a long-standing mystery in exoplanet science.
David Sing from the Johns Hopkins University (JHU), who led a parallel study, highlighted the significance of WASP-107 b as a target for Webb’s observations, stating, “WASP-107 b is such an interesting target for Webb because it’s significantly cooler and more Neptune-like in mass than many of the other low-density planets, the hot Jupiters, we’ve been studying. As a result, we should be able to detect methane and other molecules that can give us information about its chemistry and internal dynamics that we can’t get from a hotter planet.”
By providing unprecedented insights into the internal dynamics and composition of exoplanets, the James Webb Space Telescope continues to unravel the mysteries of the cosmos, opening new frontiers in our understanding of distant worlds.
Journal Reference
Welbanks, L., Bell, T. J., Beatty, T. G., Line, M. R., Ohno, K., Fortney, J. J., Schlawin, E., Greene, T. P., Rauscher, E., McGill, P., Murphy, M., Parmentier, V., Tang, Y., Edelman, I., Mukherjee, S., Wiser, L. S., Lagage, P., Dyrek, A., & Arnold, K. E. (2024). A high internal heat flux and large core in a warm neptune exoplanet. Nature, 1-3. DOI: 10.1038/s41586-024-07514-w
Sing, D.K., Rustamkulov, Z., Thorngren, D.P. et al. A warm Neptune’s methane reveals core mass and vigorous atmospheric mixing. Nature (2024). DOI: 10.1038/s41586-024-07395-z
Achrène Dyrek, Michiel Min, Leen Decin, Jeroen Bouwman, Nicolas Crouzet, Paul Mollière, Pierre-Olivier Lagage, Thomas Konings, Pascal Tremblin, Manuel Güdel, John Pye, Rens Waters, Thomas Henning, Bart Vandenbussche, Francisco Ardevol Martinez, Ioannis Argyriou, Elsa Ducrot, Linus Heinke, Gwenael van Looveren, Olivier Absil, David Barrado, Pierre Baudoz, Anthony Boccaletti, Christophe Cossou, Alain Coulais, Billy Edwards, René Gastaud, Alistair Glasse, Adrian Glauser, Thomas P. Greene, Sarah Kendrew, Oliver Krause, Fred Lahuis, Michael Mueller, Goran Olofsson, Polychronis Patapis, Daniel Rouan, Pierre Royer, Silvia Scheithauer, Ingo Waldmann, Niall Whiteford, Luis Colina, Ewine F. van Dishoeck, Göran Östlin, Tom P. Ray & Gillian Wright. SO2, silicate clouds, but no CH4 detected in a warm Neptune. Nature 625, 51–54 (2024). DOI: 10.1038/s41586-023-06849-0
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