When close-in planets have their orbits oriented just right, they can appear to pass behind their parent star once every orbit. Since these planets are very hot, it is possible to detect the disappearance and reappearance of their thermal emission (they glow like coals) during this “secondary eclipse” (the “primary eclipse” is also called a “transit”, when the planet passes in front of the star). The Spitzer Space Telescope was the first to detect this phenomenon, but it is a very small effect and so remains very difficult to detect from the ground.
My postdoc Ming Zhao, in his capacity as a researcher with the Center for Exoplanets and Habitable Worlds, has recently worked with folks at Palomar and Caltech to get the famed 200-inch Hale telescope’s WIRC instrument up to the task of making these measurements from the ground. This is a big deal because Spitzer won’t be with us much longer, and there are few other options for measuring these important properties of transiting planets. Now, we can hopefully expect a lot more of these measurements from the “Big Eye” at Palomar, and to learn a lot about how these planet’s atmospheres work!
Ming Zhao writes about his efforts here.