A map of the day-night contrast of the extrasolar planet HD 189733b

TL;DR

This study maps the temperature distribution of the hot Jupiter HD 189733b, revealing efficient atmospheric heat redistribution and an eastward-shifted hot spot, challenging previous assumptions about similar exoplanets.

Contribution

It provides the first temperature map of HD 189733b's atmosphere, showing efficient heat transport and a hot spot offset, based on detailed infrared observations.

Findings

Temperature range: 973-1212 K at 8 microns

Efficient energy redistribution across the atmosphere

Hot spot shifted east of substellar point

Abstract

"Hot Jupiter" extrasolar planets are expected to be tidally locked because they are close (<0.05 astronomical units, where 1 AU is the average Sun-Earth distance) to their parent stars, resulting in permanent daysides and nightsides. By observing systems where the planet and star periodically eclipse each other, several groups have been able to estimate the temperatures of the daysides of these planets. A key question is whether the atmosphere is able to transport the energy incident upon the dayside to the nightside, which will determine the temperature at different points on the planet's surface. Here we report observations of HD 189733, the closest of these eclipsing planetary systems, over half an orbital period, from which we can construct a 'map' of the distribution of temperatures. We detected the increase in brightness as the dayside of the planet rotated into view. We estimate a minimum brightness temperature of 973 +/- 33 K and a maximum brightness temperature of 1212 +/- 11 K at a wavelength of 8 microns, indicating that energy from the irradiated dayside is efficiently redistributed throughout the atmosphere, in contrast to a recent claim for another hot Jupiter. Our data indicate that the peak hemisphere-integrated brightness occurs 16$\pm$6 degrees before opposition, corresponding to a hot spot shifted east of the substellar point. The secondary eclipse (when the planet moves behind the star) occurs 120 +/- 24 s later than predicted, which may indicate a slightly eccentric orbit.