NASA's Spitzer Space Telescope is allowing astronomers to study the atmosphere of "hot Jupiter" planets orbiting in the blistering heat of distant stars.
In the new study, Nikole Lewis of the Massachusetts Institute of Technology, Cambridge and colleagues made the longest Spitzer observation yet of a hot Jupiter.
The infrared telescope stared at the HAT-P-2 system continuously for six days, watching it cross in front of its star, slip behind, and then reappear on the other side, making a full orbit.
What makes the observation even more exciting is that the planet has a comet-like eccentric orbit, carrying it as close as 4.5 million kilometres to the star and out to as far as 15 million kilometre.
"It's as if nature has given us a perfect lab experiment with this system," said Heather Knutson, a co-author of the new paper at the California Institute of Technology, Pasadena.
"Because the planet's distance to the Sun changes, we can watch how fast it takes to heat up and cool down. It's as though we're turning the heat knob up on our planet and watching what happens," said Knutson.
The new HAT-P-2b study is also one of the first to use multiple wavelengths of infrared light, instead of just one, while watching a full orbit of a hot Jupiter. This enables the scientists to peer down into different layers of the planet.
The results reveal that HAT-P-2b takes about a day to heat up as it approaches the hottest part of its orbit, and four to five days to cool down as it swings away.
It also exhibits a temperature inversion - a hotter, upper layer of gas - when it is closest to its star. What's more, the carbon chemistry of the planet seems to be behaving in unexpected ways, which the astronomers are still trying to understand.
"These planets are much hotter and more dynamic than our own Jupiter, which is sluggish by comparison. Strong winds are churning material up from below, and the chemistry is always changing," said Lewis.
In addition to our solar system's eight planets, there are more than 800 so-called exoplanets known to circle stars beyond our Sun.
