Fortunately, because HAT-P-2b's orbit is not only compact but also eccentric, astronomers have a wonderful opportunity to see these changes occur over a very short timescale.
"It's as if nature has given us a perfect lab experiment with this system," said Heather Knutson, of the California Institute of Technology (Caltech), Pasadena, Calif. (pictured top, poking a simulated exoplanet). "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."
Spitzer analyzed the infrared light from the exoplanet throughout its orbit. By measuring radiation of different wavelengths, the team of astronomers were able to take a peek at the dynamics of several different layers of HAT-P-2b's atmosphere, adding depth to the observation. This is the first time a multi-wavelength infrared campaign has been carried out on an exoplanet.
As the exoplanet swings toward the star, the Spitzer data revealed it takes about one day for the exoplanetary atmosphere to heat up before reaching closest approach (periastron). It then takes four to five days to cool down. Because the astronomers had access to temperature-depth measurements, they found that there was a temperature inversion at the hottest point in its orbit - a hotter upper atmospheric layer formed while the lower layers were maintained at a lower temperature.