Astronomers have observed a distant planet (upsilon Andromedae b), with a hot spot in an unexpected place. This gas-giant planet, in the hot Jupiter category, orbits its star with one face perpetually facing it. One would expect that this face would be the hottest part of the planet, but to the observers surprise, the hot spot was actually offset by a whopping 80 degrees, so that it was located on the side of the planet instead of directly under the star's glare.
The planet was observed from NASA's Spitzer Space Telescope, which was the first telescope to directly detect photons from an exoplanet (2005). Upsilon Andromedae b does not cross in front of its host star, so it was detected by measuring the total combined light from the star and the planet, as the planet orbited the star (with a period of 4.6 days). Spitzer could not see the planet directly, so it detected variations in the total infrared light from the system that occur when the hot side of a planet comes into Earth's field of view. The hottest part of the planet gives off the most infrared light, and this occurred when the planet was not directly towards or away from us, but rather when the hot Jupiter had its side facing the Earth. This would be equivalent to the Earth being warmest during sunset, as opposed to when we are directly under the sun!
Previous observations have shown slight variations in the hot spots of these so-called hot Jupiters, which were thought to be due to fierce winds pushing around hot material, but this observation may throw this theory into question. The findings show that astronomers understand less about the atmospheric energetics than they previously thought, and this is opening the floor for some new theories. One speculation involves star-planet magnetic interactions, but the several emerging theories will be tested against a growing pool of examined hot Jupiters.
Studying how these distant solar systems form and evolve can provide us with crucial information that will help astrobiologists determine where to search for habitable worlds.