Precise Constraints on the Energy Budget of WASP-121 b from its JWST NIRISS/SOSS Phase Curve
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| Format: | Preprint |
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2025
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| author | Splinter, Jared Coulombe, Louis-Philippe Frazier, Robert C. Cowan, Nicolas B. Rauscher, Emily Dang, Lisa Radica, Michael Collins, Sean Pelletier, Stefan Allart, Romain MacDonald, Ryan J. Lafrenière, David Albert, Loïc Benneke, Björn Doyon, René Jayawardhana, Ray Johnstone, Doug Krishnamurthy, Vigneshwaran Piaulet-Ghorayeb, Caroline Kaltnegger, Lisa Meyer, Michael R. Taylor, Jake Turner, Jake D. |
| author_facet | Splinter, Jared Coulombe, Louis-Philippe Frazier, Robert C. Cowan, Nicolas B. Rauscher, Emily Dang, Lisa Radica, Michael Collins, Sean Pelletier, Stefan Allart, Romain MacDonald, Ryan J. Lafrenière, David Albert, Loïc Benneke, Björn Doyon, René Jayawardhana, Ray Johnstone, Doug Krishnamurthy, Vigneshwaran Piaulet-Ghorayeb, Caroline Kaltnegger, Lisa Meyer, Michael R. Taylor, Jake Turner, Jake D. |
| contents | Ultra-hot Jupiters exhibit day-to-night temperature contrasts upwards of 1000 K due to competing effects of strong winds, short radiative timescales, magnetic drag, and H2 dissociation/recombination. Spectroscopic phase curves provide critical insights into these processes by mapping temperature distributions and constraining the planet's energy budget across different pressure levels. Here, we present the first NIRISS/SOSS phase curve of an ultra-hot Jupiter, WASP-121 b. The instrument's bandpass [0.6 - 2.85 micron] captures an estimated 50-83% of the planet's bolometric flux, depending on orbital phase, allowing for unprecedented constraints on the planet's global energy budget; previous measurements with HST/WFC3 and JWST/NIRSpec/G395H captured roughly 20% of the planetary flux. Accounting for the unobserved regions of the spectrum, we estimate effective day and nightside temperatures of T_day = 2717 +/- 17 K and T_night = 1562 +/- 19 K corresponding to a Bond albedo of A_B = 0.277 +/- 0.016 and a heat recirculation efficiency of epsilon = 0.246 +/- 0.014. Matching the phase-dependent effective temperature with energy balance models yields a similar Bond albedo of 0.3 and a mixed layer pressure of 1 bar consistent with photospheric pressures, but unexpectedly slow winds of 0.2 km/s, indicative of inefficient heat redistribution. The shorter optical wavelengths of the NIRISS/SOSS Order 2 yield a geometric albedo of A_g = 0.093 +/- 0.029 (3 sigma upper limit of 0.175), reinforcing the unexplained trend of hot Jupiters exhibiting larger Bond albedos than geometric albedos. We also detect near-zero phase curve offsets for wavelengths above 1.5 micron, consistent with inefficient heat transport, while shorter wavelengths potentially sensitive to reflected light show eastward offsets. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_09760 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Precise Constraints on the Energy Budget of WASP-121 b from its JWST NIRISS/SOSS Phase Curve Splinter, Jared Coulombe, Louis-Philippe Frazier, Robert C. Cowan, Nicolas B. Rauscher, Emily Dang, Lisa Radica, Michael Collins, Sean Pelletier, Stefan Allart, Romain MacDonald, Ryan J. Lafrenière, David Albert, Loïc Benneke, Björn Doyon, René Jayawardhana, Ray Johnstone, Doug Krishnamurthy, Vigneshwaran Piaulet-Ghorayeb, Caroline Kaltnegger, Lisa Meyer, Michael R. Taylor, Jake Turner, Jake D. Earth and Planetary Astrophysics Ultra-hot Jupiters exhibit day-to-night temperature contrasts upwards of 1000 K due to competing effects of strong winds, short radiative timescales, magnetic drag, and H2 dissociation/recombination. Spectroscopic phase curves provide critical insights into these processes by mapping temperature distributions and constraining the planet's energy budget across different pressure levels. Here, we present the first NIRISS/SOSS phase curve of an ultra-hot Jupiter, WASP-121 b. The instrument's bandpass [0.6 - 2.85 micron] captures an estimated 50-83% of the planet's bolometric flux, depending on orbital phase, allowing for unprecedented constraints on the planet's global energy budget; previous measurements with HST/WFC3 and JWST/NIRSpec/G395H captured roughly 20% of the planetary flux. Accounting for the unobserved regions of the spectrum, we estimate effective day and nightside temperatures of T_day = 2717 +/- 17 K and T_night = 1562 +/- 19 K corresponding to a Bond albedo of A_B = 0.277 +/- 0.016 and a heat recirculation efficiency of epsilon = 0.246 +/- 0.014. Matching the phase-dependent effective temperature with energy balance models yields a similar Bond albedo of 0.3 and a mixed layer pressure of 1 bar consistent with photospheric pressures, but unexpectedly slow winds of 0.2 km/s, indicative of inefficient heat redistribution. The shorter optical wavelengths of the NIRISS/SOSS Order 2 yield a geometric albedo of A_g = 0.093 +/- 0.029 (3 sigma upper limit of 0.175), reinforcing the unexplained trend of hot Jupiters exhibiting larger Bond albedos than geometric albedos. We also detect near-zero phase curve offsets for wavelengths above 1.5 micron, consistent with inefficient heat transport, while shorter wavelengths potentially sensitive to reflected light show eastward offsets. |
| title | Precise Constraints on the Energy Budget of WASP-121 b from its JWST NIRISS/SOSS Phase Curve |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2509.09760 |