The last decade has seen a bonanza of exoplanet discoveries. Nearly 2,000 exoplanets -- planets outside our solar system -- have been confirmed so far, and more than 5,000 candidate exoplanets have been identified. Many of these exotic worlds belong to a class known as "hot Jupiters." These are gas giants like Jupiter but much hotter, with orbits that take them feverishly close to their stars.
The Spitzer results show that HD 80606b does not dissipate much heat when it is squeezed by gravity during its close encounters - and thus is not squishy, but rather stiffer as a whole. This suggests the planet is not circularizing its orbit as fast as expected, and may take another 10 billion years or more to complete.
A rotation rate of 90 hours is much slower than what is predicted for HD 80606b, puzzling astronomers, and adding to the enduring mystique of hot Jupiters.
For more information about Spitzer, visit: http://spitzer.caltech.edu / http://www.nasa.gov/spitzer
Technical journal article: http://iopscience.iop.org/article/10.3847/2041-8205/820/2/L33
Jet Propulsion Laboratory, Pasadena, California