WASHINGTON: In a maiden attempt to decode the rotation of a massive exoplanet, astronomers using Hubble Space Telescope have measured the rotation rate of a cloudy "super-Jupiter" by observing the varied brightness in its atmosphere.

The planet called 2M1207b is about four times more massive than Jupiter. It is a companion to a failed star known as a brown dwarf, orbiting the object at a distance of five 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.

"The result is very exciting. It gives us a unique technique to explore the atmospheres of exoplanets and to measure their rotation rates," said Daniel Apai from University of Arizona in Tucson.

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 colorless.

The observations revealed that the exoplanet's atmosphere is hot enough to have "rain" clouds made of silicates - vaporised 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," added Yifan Zhou from University of Arizona and lead author.

The "super-Jupiter" is so hot that it appears brightest in infrared light. 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.

The planet, however, will not maintain these sizzling temperatures. 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 also determined that the super-Jupiter completes one rotation approximately every 10 hours, spinning at about the same fast rate as Jupiter.

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 noted in a paper appeared in The Astrophysical Journal.

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