Scientists forecast weather on planets outside our solar system

An artist's rendering of an exoplanet that exhibits a typical weather pattern of cloudy mornings and clear, scorching afternoons(Credit: Lisa Esteves)

Great news if you're planning a visit to exoplanets Kepler-7b or HAT-P-7b. An international team of astrophysicists has identified daily weather cycles using Kepler telescope data on these and four other far off worlds. The nightly news isn't about to start reading extrasolar weather reports, but this new knowledge will help improve our understanding of the Earth's place in the cosmic puzzle.

The study, which comes from a collaboration between the University of Toronto, York University, and Queen's University Belfast, examined four-and-a-half years of observations from the Kepler Space Telescope, which looks for and monitors thousands of confirmed and unconfirmed exoplanets as part of the ongoing search for Earth-like planets in the universe. Kepler discovered clouds on extrasolar planets for the first time back in 2013.

The researchers' analysis found 14 exoplanets with significant phase curve (variations in brightness) data, and further analysis from there revealed six that exhibit distinctly different phases. As planets and their moons go about their orbit and rotations, they reflect light from their parent stars. The intensity of that light varies depending on local atmospheric conditions and lunar phases.

"We determined the weather on these alien worlds by measuring changes as the planets circle their host stars, and identifying the day-night cycle," said the study's lead author Lisa Esteves. "We traced each of them going through a cycle of phases in which different portions of the planet are illuminated by its star, from fully lit to completely dark."

The hottest two planets of the six exhibited excess brightness when the evening side is visible, which suggests that winds transport heat from thermal emission to that side. The other four, which are much cooler, had excess brightness on the morning side, most likely because of reflected starlight.

The cooler planets appear to have cloudy mornings and clear, scorching-hot afternoons. Wind transports clouds from the evening side to the morning side, where the planet's star heats them and they soon dissipate.

The hotter planets are likely too hot to support the formation of clouds, so their weather patterns are dictated by the eastward shift of a hot spot.

"The detection of light from these planets hundreds to thousands of light years away is on its own remarkable," said study co-author Dr. Ernst de Mooij. "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."

Another co-author, Ray Jayawardhana, added that upcoming space missions will probably reveal more small planets around bright stars that could be studied in more detail. "Someday soon we hope to be talking about weather reports for alien worlds not much bigger than Earth, and to be making comparisons with our home planet," he said.

A paper describing the research was published in The Astrophysical Journal.

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