This is an illustration of a planet that is four times the mass of Jupiter and orbits 5 billion miles from a brown-dwarf companion (the bright red object seen in the background). The rotation rate of this “super-Jupiter” has been measured by studying subtle variations in the infrared light the hot planet radiates through a variegated, cloudy atmosphere. The planet completes one rotation every 10 hours — about the same rate as Jupiter. Because the planet is young, it is still contracting under gravity and radiating heat. The atmosphere is so hot that it rains molten glass and, at lower altitudes, molten iron. Because the planet is only 170 light-years away, many of the bright background stars that can be seen from Earth can be seen from the planet’s location in our galaxy, including Sirius, Fomalhaut, and Alpha Centauri. Our sun is a faint star in the background, located midway between Procyon and Altair. Credit: Artwork: NASA, ESA, and G. Bacon (STScI); Science: NASA, ESA, Y. Zhou and D. Apai (U. Arizona)
Astronomers using Hubble have measured the rotation rate of an extreme exoplanet 2M1207b by observing the varied brightness in its atmosphere. This is the first measurement of the rotation of a massive exoplanet using direct imaging. “The result is very exciting,” said Daniel Apai of the Uni of Arizona in Tucson. “It gives us a unique technique to explore the atmospheres of exoplanets and to measure their rotation rates.”
The planet is about 4X more massive than Jupiter and is dubbed a “super-Jupiter.” It is a companion to a failed star known as a brown dwarf, orbiting the object at a distance of 5 billion miles. By contrast, Jupiter is approximately 500 million miles from the sun. The brown dwarf is known as 2M1207. The system resides 170 light-years away from Earth.
Hubble’s image stability, high resolution, and high-contrast imaging capabilities allowed astronomers to precisely measure the planet’s brightness changes as it spins. The researchers attribute the brightness variation to complex clouds patterns in the planet’s atmosphere. The new Hubble measurements not only verify the presence of these clouds, but also show that the cloud layers are patchy and 3colorless.
Astronomers first observed the massive exoplanet 10 years ago with Hubble. The observations revealed that the exoplanet’s atmosphere is hot enough to have “rain” clouds made of silicates: vaporized rock that cools down to form tiny particles with sizes similar to those in cigarette smoke. Deeper into the atmosphere, iron droplets are forming and falling like rain, eventually evaporating as they enter the lower levels of the atmosphere. “So at higher altitudes it rains glass, and at lower altitudes it rains iron,” said Yifan Zhou “The atmospheric temperatures are between about 2,200 to 2,600 degrees Fahrenheit.”
The super-Jupiter is so hot that it appears brightest in infrared light. Astronomers used Hubble’s Wide Field Camera 3 to analyze the exoplanet in infrared light to explore the object’s cloud cover and measure its rotation rate. The planet is hot because it is only about 10 million years old and is still contracting and cooling. For comparison, Jupiter in our solar system is about 4.5 billion years old. Over the next few billion years, the object will cool and fade dramatically. As its temperature decreases, the iron and silicate clouds will also form lower and lower in the atmosphere and will eventually disappear from view.
Zhou and his team have also determined that the super-Jupiter completes 1 rotation approximately every 10 hours, spinning at about the same fast rate as Jupiter. This super-Jupiter is only about five to seven times less massive than its brown-dwarf host. By contrast, our sun is about 1,000 times more massive than Jupiter. “So this is a very good clue that the 2M1207 system we studied formed differently than our own solar system,” Zhou explained. The planets orbiting our sun formed inside a circumstellar disk through accretion. But the super-Jupiter and its companion may have formed throughout the gravitational collapse of a pair of separate disks.
“Our study demonstrates that Hubble and its successor, NASA’s James Webb Space Telescope, will be able to derive cloud maps for exoplanets, based on the light we receive from them,” Apai said. Webb will give better atmospheric composition and derive detailed maps from brightness changes.
http://hubblesite.org/newscenter/archive/releases/2016/05/full/
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