Astronomers using the HARPS planet-hunting machine at European Southern Observatory's (ESO) La Silla Observatory in Chile have made the first-ever direct detection of the spectrum of visible light reflected off an exoplanet. These observations also revealed new properties of this famous object, the first exoplanet ever discovered around a normal star: 51 Pegasi b. The result promises an exciting future for this technique, particularly with the advent of next generation instruments, such as ESPRESSO, on the Very Large Telescope (VLT), and future telescopes, such as the E-ELT.
The exoplanet 51 Pegasi b lies some 50 light-years from Earth in the constellation of Pegasus. It was discovered in 1995 and was the first confirmed exoplanet to be found orbiting an ordinary star like the sun. It is also regarded as the archetypal hot Jupiter - a class of planets now known to be relatively commonplace, which are similar in size and mass to Jupiter, but orbit much closer to their parent stars.
The host star's spectrum is used as a template to guide a search for a similar signature of light that is expected to be reflected off the planet as it describes its orbit. This is a difficult task as planets are dim in comparison to their parent stars. The signal from the planet is also easily swamped by other tiny effects and sources of noise.
"This type of detection technique is of great scientific importance, as it allows us to measure the planet's real mass and orbital inclination, which is essential to more fully understand the system," Martins said, according to a press release. "It also allows us to estimate the planet's reflectivity, or albedo, which can be used to infer the composition of both the planet's surface and atmosphere."
"We are now eagerly awaiting first light of the ESPRESSO spectrograph on the VLT so that we can do more detailed studies of this and other planetary systems," said co-author Nuno Santos.
This research was presented in a paper "Evidence for a spectroscopic direct detection of reflected light from 51 Peg b", by J. Martins et al., to appear in the journal Astronomy & Astrophysics on April 22.
