Cloudy Mornings & Hot Afternoons on Alien Worlds

Artist's interpretation of a cloudy exoplanet. Image Credit: Courtesy Space Telescope Science Instutute

Artist’s interpretation of a cloudy exoplanet. Image Credit: Courtesy Space Telescope Science Instutute

We may complain a lot about the weather on earth but perhaps we are much better off here than on some alien worlds, where the daily forecast is cloudy, overcast skies in the morning and scorching heat in the afternoon.

A team of international astronomers including York University scientist Professor Ray Jayawardhana have uncovered evidence of daily weather cycles on six extra-solar planets using sensitive observations from the Kepler space telescope.

“Despite the discovery of thousands of extra-solar planets, what these far-off worlds look like is still shrouded in mystery,” says lead author Lisa Esteves, graduate student at the University of Toronto.

In their paper entitled “Changing Phases of Alien Worlds: Probing Atmospheres of Kepler Planets with High-Precision Photometry” published today in the Astrophysical Journal, the team analyzed all 14 Kepler planets known to exhibit phase variations, and found indications of cloudy mornings on four and hot, clear afternoons on two others.

Most of the worlds examined in the study were very hot and large, with temperatures greater than 1600 degrees Celsius and sizes comparable to Jupiter. These conditions are far from hospitable to life, but excellent for phase measurements, the authors note.

“We are getting to know these exotic alien planets as dynamic, three-dimensional worlds through remote sensing across vast distances. Someday soon we hope to provide similar weather reports for worlds not much bigger than the Earth,” says study co-author Jayawardhana, who adds that upcoming space missions such as TESS (2017) and PLATO (2024) should reveal many small planets around bright stars, making great targets for detailed studies.

For the study, the researchers determined weather on these alien worlds by measuring phase changes as the planets circle their host stars. Similar to the Moon in the solar system, an exoplanet going through a cycle of phases can be traced, from fully lit to completely dark, when different portions of the planet are illuminated by its star.

“The detection of the light from these far-away planets, some of which took thousands of years to reach us, is in itself remarkable,” says co-author Ernst de Mooij of Queen’s University Belfast, UK. “But when we consider that phase cycle variations can be up to 100,000 times fainter than the host star, these detections become truly astonishing.”

The Kepler space telescope was the ideal instrument for the study of exoplanet phase variations, according to the researchers. The telescope’s very precise measurements and the vast amount of data it collected over its initial four-year mission allowed astronomers to beat the noise and measure the tiny signals from these distant worlds.

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