【惑星科学】夜側が暑く昼側がもっと暑い巨大地球型惑星

Atmospheric and surface temperature measurements of a super-Earth exoplanet - a planet outside our Solar System with a mass between one and ten times that of Earth - are published in Nature this week. The thermal map of the super-Earth, named 55 Cancri e, shows that the planet is very hot but still experiences a strong temperature difference between its dayside and its nightside, suggesting that processes found in planets within our Solar System, such as high winds or lava flows, are at work on distant worlds.

Over the past decade, observations have provided key insights into the atmospheres of giant exoplanets. However, the properties of lower-mass exoplanets remain largely unknown.

Brice-Olivier Demory and colleagues report a longitudinal thermal brightness map of nearby 55 Cancri e, which is less than twice the size of Earth. They monitored infrared emissions from the planet with the Spitzer Space Telescope Infrared Array Camera and found that the planet’s nightside temperature is around 1,380 kelvin (1,107 degrees Celsius), with the dayside temperature about 1,300 kelvin (1,027 degrees Celsius) hotter at 2,700 kelvin (2,427 degrees Celsius). The authors also identify a hot spot that they suggest stems from either strong atmospheric winds or low-viscosity lava flows at the planetary surface. They conclude that an additional, currently unknown source of heat is required to explain the observed infrared emission.