Weather Report for Distant Planet: Variable Heat Wave

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As mentioned in a previous article today about global warming, we on Earth worry about our planet’s atmosphere rising by a few degrees on average over the next century. But imagine living on a planet where temperatures could rise 700 degrees in just a few hours! A distant planet known as HD80606b, is a gas giant orbiting a star 200 light-years from Earth. It’s extremely eccentric orbit around the star takes it from a relatively comfortable distance in an Earth-like habitable zone to the blazing hot regions much closer than Mercury is to our Sun. Infrared sensors aboard NASA’s Spitzer Space Telescope measured the planet’s temperature as it swooped close to the star, observing a planetary heat wave that rose from 800 to 1,500 degrees Kelvin (980 to 2,240 degrees Fahrenheit) in just six hours. Wow!

And for those readers who like to complain about artist impressions images, the image here is a novel type of “photorealistic” image, created by a new computer program that calculates the radiative transfer processes in astrophysics.

“We can’t get a direct image of the planet, but we can deduce what it would look like if you were there. The ability to go beyond an artist’s interpretation and do realistic simulations of what you would actually see is very exciting,” said Gregory Laughlin, professor of astronomy and astrophysics at UCSC. Laughlin is lead author of a new report on the findings published this week in Nature.

“This is the first time that we’ve detected weather changes in real time on a planet outside our solar system,” said Laughlin “The results are very exciting because they give us important clues to the atmospheric properties of the planet.”

Spitzer observed the planet for 30 hours before, during, and just after its closest approach to the star. The planet passed behind the star (an event called a secondary eclipse) just before the moment of its closest approach. This was a lucky break for Laughlin and his colleagues, who had not known that would happen when they planned the observation. The secondary eclipse allowed them to get accurate measurements from just the star and thereby determine exact temperatures for the planet.

HD80606b has an estimated mass of about four times that of Jupiter and completes its orbit in about 111 days. At its closest approach to the star it experiences radiation about 800 times stronger than when it is most distant.

At the closest point, the sunlight beating down on the planet is 825 times stronger than the irradiation it receives at its farthest point from the star. “If you could float above the clouds of this planet, you’d see its sun growing larger and larger at faster and faster rates, increasing in brightness by almost a factor of 1,000,” Laughlin said.

“Even after finding nearly 200 planets, the diversity and oddness of these new worlds continues to amaze and confound me,” says Paul Butler of the Carnegie Institution for Science’s Department of Terrestrial Magnetism. Butler made the precision velocity measurements of the host star that allowed the planet’s orbit to be calculated. Butler’s work has uncovered about half of the known extra-solar planets.

Daniel Kasen, a Hubble postdoctoral fellow at UCSC, was able to generate the image with the new program. “It calculates the color and intensity of light coming from the glowing planet, and also how starlight would reflect off the surface of the planet,” Kasen said.

The resulting image shows a thin blue crescent of reflected starlight framing the night side of the planet, which glows cherry red from its own heat, like coals in a fire. “These images are far more realistic than anything that’s been done before for extrasolar planets,” Laughlin said.

The planet is expected to pass in front of its star when viewed from Earth on February, and the team will be watching again.

Sources: EurekAlert, UCSC