Weather report on alien planets: Cloudy, high of 3,000

An artist's rendering of an exoplanet with cloudy mornings and clear, scorching afternoons, exhibiting a cycle of phase variations that occur as different portions of the planet are illuminated by its star, as seen from Earth. Astronomers at the University of Toronto, York University and Queen's University Belfast used measurements of the phase variations of six exoplanets obtained by the Kepler space telescope to forecast their daily weather cycle.

Image: Lisa Esteves/University of Toronto

The search for Earth-like planets has consumed astronomers of late, with scores being found orbiting habitable zones of distant stars. Yet little is known about the weather on these alien worlds - until now.

"Despite the discovery of thousands of extra-solar planets, what these far-off worlds look like is still shrouded in mystery," Lisa Esteves, graduate student at the University of Toronto, who led a study of 14 exoplanets that appeared in the Astrophysical Journal Tuesday.

Using sensitive observations from the Kepler space telescope, Esteves and her colleagues found conditions might an extreme version of what earthlings are used to. These planets appear to have cloudy, overcast skies in the mornings and scorching heat in the afternoons, with temperatures reaching to 1,600 degrees Celsius, or 2,912 F.

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.

Kepler proved the ideal tool to examine the weather patterns. With its precise measurements and vast amounts of data collected over its four-year mission, the telescope allowed astronomers to beat the noise and measure tiny signals from these distant worlds.

"The detection of the light from these far-away planets, some of which took thousands of years to reach us, is in itself remarkable," said Ernst de Mooij, a co-author on the study from 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."

With temperatures greater than 1,600 C, conditions on these large planets (which are about the size of Jupiter) are far from hospitable to life, but excellent for phase measurements.

"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," said York University's Ray Jayawardhana, another co-author of the study.

  • Michael Casey

    Michael Casey covers the environment, science and technology for