Scientists measured the temperature of a Jupiter-like gas giant called Upsilon Andromeda b:
This artist's concept shows a Jupiter-like planet soaking up the scorching rays of its nearby star. A similar gas-giant planet, called Upsilon Andromeda b, has one face that is perpetually cold and dark, and another that forever blisters under the heat of its star. According to astronomers who studied the planet using NASA's Spitzer Space Telescope, the side of the planet facing the star is as hot as lava (between 2,550 and 3,000 degrees F), while the other side is as cold as ice (between minus 4 and 450 degrees F). The researchers believe the atmosphere of the planet absorbs and re-radiates light so fast that heated gases circulating around the planet cool off before reaching the dark side.
For the first time, astronomers have measured the day and night temperatures of a planet outside our solar system. The team revealed that a giant Jupiter-like gas planet orbiting very close to its star is blisteringly hot on one side, and frigid on the other.