Exoplanet 51 Pegasi b has just been imaged for the first time in visible light. This is the first time ever that a world orbiting a star other than the sun has been recorded in the visible part of the electromagnetic spectrum.
This giant world is a member of a class of "hot Jupiters," which includes other massive planets orbiting close to their stars. The alien planet, popularly known by an informal name of Bellerophon, sits around 50 light years from Earth, orbiting the star 51 Pegasi in the constellation of Pegasus. This planet made history as the first exoplanet to ever be discovered orbiting a star much like our own sun.
Astronomers captured this new image utilizing the High Accuracy Radial velocity Planet Searcher (HARPS) instrument attached to the 140-inch telescope at the La Silla Observatory in Chile. The HARPS detector produces spectrographs, rainbows of light that can reveal details of the celestial objects being observed, including their chemical composition.
Most studies of the atmosphere of exoplanets depends on waiting until the world passes in front of its star, as seen from Earth. Thermal readings can also be obtained when the planet passes behind its local star. This technique is only possible in systems where the orbit of the planet is aligned in such a way that it passes between its sun and our home planet. The HARPS instrument is not limited in this way, potentially vastly increasing the number of exoplanets that may be studied by astronomers.
"This type of detection technique is of great scientific importance, as it allows us to measure the planet's realmass and orbital inclination, which is essential to more fully understand the system. 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," Jorge Martins of the Universidade do Porto in Portugal said.
Analysis of the HARPS data reveals that 51 Pegasi b is slightly larger than the planet Jupiter, although it only contains roughly half the mass of that giant world. Astronomers with the European Southern Observatory (ESO), which operates the observatory, determined the world is highly-reflective, and that its orbit is inclined roughly nine degrees to a straight line between 51 Pegasi and the sun.
"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 an exceedingly difficult task as planets are incredibly dim in comparison to their dazzling parent stars," ESO officials explained in a press release.
Since the discovery of 51 Pegasi b 20 years ago, more than 1,900 other exoplanets have been found in 1,200 star systems.
