Revisiting the Iconic Spitzer Phase Curve of 55 Cancri e: Hotter Dayside, Cooler Nightside, and Smaller Phase Offset
Samson J. Mercier, Lisa Dang, Alexander Gass, Nicolas B. Cowan, Taylor J. Bell
Abstract
Abstract Thermal phase curves of short-period exoplanets provide the best constraints on the atmospheric dynamics and heat transport in their atmospheres. The published Spitzer Space Telescope phase curve of 55 Cancri e, an ultra-short-period super-Earth, exhibits a large phase offset suggesting significant eastward heat recirculation, unexpected on such a hot planet. We present our rereduction and analysis of these iconic observations using the open source and modular Spitzer Phase Curve Analysis pipeline. In particular, we attempt to reproduce the published analysis using the same instrument detrending scheme as the original authors. We retrieve the dayside temperature ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>day</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>3771</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>520</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>669</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> K), nightside temperature ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mi>night</mml:mi> <mml:mspace width="0.25em"/> </mml:mrow> </mml:msub> <mml:mo><</mml:mo> <mml:mn>1649</mml:mn> </mml:math> K at 2σ), and longitudinal offset of the planet's hot spot, and quantify how they depend on the reduction and detrending. Our reanalysis suggests that 55 Cancri e has a negligible hot spot offset of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>12</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>18</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>21</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> degrees east. The small phase offset and cool nightside are consistent with the poor heat transport expected on ultra-short-period planets. The high dayside 4.5 μ m brightness temperature is qualitatively consistent with SiO emission from an inverted rock vapor atmosphere.