Planets outside our solar system, also called extrasolar planets, would consider Earth’s strongest winds mere breezes.
Earth’s inhabitants are used to temperatures that vary, sometimes greatly, between day and night. New measurements for three planets outside our solar system indicate their temperatures remain fairly constant — and blazing hot — from day to night, even though it is likely one side of each planet always faces its sun and the other is in permanent darkness.
The reason apparently is supersonic winds, perhaps as strong as 9,000 miles an hour that constantly churn the planets’ atmospheres and keep temperatures on the dark side from plunging.
The planets, gas giants similar in size to Jupiter, were discovered in the last decade orbiting stars about the same size as our sun and less than 150 light years from Earth. All of them orbit within about 5 million miles of their stars, far less than Mercury’s distance from our sun.
Eric Agol, a University of Washington assistant professor of astronomy and co-author of a poster presented at the American Astronomical Society national meeting in Seattle says the temperatures appear to be constant day and night on these planets because strong winds mix the atmosphere planetwide.
“We can’t say for sure that we’ve ruled out significant day-night temperature differences, but it seems unlikely there is a very big contrast based on our measurements and what we know about these systems,” said Agol, who is lead scientist for a project using the Spitzer Space Telescope to measure the temperature properties of extrasolar planets.
Agol and colleagues Nicolas Cowan, a UW astronomy doctoral student and lead author of the poster, and David Charbonneau of the Harvard-Smithsonian Center for Astrophysics, measured infrared light from three planetary systems at eight different positions in their orbits in late 2005. They measured the thermal brightness of the systems when the planets’ day sides faced the Earth, when the night sides faced the Earth and at various phases in between. They detected no infrared brightness variations in any of the systems, suggesting there are not big differences in temperatures on the day and night sides.
Instead the planets appear to have a fairly uniform temperature of about 925 degrees Celsius, or about 1700 degrees Fahrenheit.
Measuring the planets’ temperatures is a painstaking process because a planet’s radiation is drowned out by the light from its parent star. Even when a planet goes behind the host star and disappears completely from view, the decline in light from the entire system is almost imperceptible, on the order of 0.25 percent, Agol said. Making the observations requires precise calibration and light measurements.
The three planets are 51 Pegasi, about 50 light years from our sun, HD179949b, about 100 light years distant, and HD209458b, about 147 light years away. A light year is about 5.88 trillion miles. In 1995, 51 Pegasi became the first planet orbiting another star to be discovered. Since then numerous planets — gas giants the mass of Jupiter or larger — have been observed from Earth. Most orbit very close to their stars. A common theory is that they formed far away from their stars, perhaps in about the same position as Jupiter is to our sun, and then migrated close to their stars. Their distance makes it difficult to gather much direct data about the planets.
To date no Earth-sized planets have been reported orbiting other stars like our sun.
